PROJJSON: rename file as projjson.schema.json, and add versionning to it and to exported PROJJSON strings

14 files changed, 1180 insertions, 63 deletions

diff --git a/data/Makefile.am b/data/Makefile.am
index 096ba7c3..d686270d 100644
--- a/data/Makefile.am
+++ b/data/Makefile.am
@@ -3,7 +3,7 @@ DATAPATH = $(top_srcdir)/data
 pkgdata_DATA = GL27 nad.lst nad27 nad83 world other.extra \
 		CH null \
 		ITRF2000 ITRF2008 ITRF2014 proj.db \
-		crsjson.schema.json
+		projjson.schema.json
 
 SQL_ORDERED_LIST = sql/begin.sql \
 		sql/proj_db_table_defs.sql \
@@ -41,7 +41,7 @@ EXTRA_DIST = GL27 nad.lst nad27 nad83 \
 		world other.extra \
 		CH \
 		ITRF2000 ITRF2008 ITRF2014 \
-		crsjson.schema.json \
+		projjson.schema.json \
 		CMakeLists.txt tests/test_nodata.gtx null \
 		generate_all_sql_in.cmake sql_filelist.cmake \
 		$(SQL_ORDERED_LIST)
diff --git a/data/crsjson.schema.json b/data/projjson.schema.json
index 726d8ece..60fca6df 100644
--- a/data/crsjson.schema.json
+++ b/data/projjson.schema.json
@@ -1,7 +1,8 @@
 {
-  "$id": "https://proj.org/crsjson.schema.json",
+  "$id": "https://proj.org/schemas/v0.1/projjson.schema.json",
   "$schema": "http://json-schema.org/draft-07/schema#",
-  "description": "Schema for CRS JSON",
+  "description": "Schema for PROJJSON",
+  "$comment": "This file exists both in data/ and in schemas/vXXX/. Keep both in sync. And if changing the value of $id, change PROJJSON_CURRENT_VERSION accordingly in io.cpp",
 
   "oneOf": [
     { "$ref": "#/definitions/crs" },
@@ -18,6 +19,7 @@
     "abridged_transformation": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["AbridgedTransformation"] },
         "name": { "type": "string" },
         "method": { "$ref": "#/definitions/method" },
@@ -38,6 +40,7 @@
     "axis": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["Axis"] },
         "name": { "type": "string" },
         "abbreviation": { "type": "string" },
@@ -109,6 +112,7 @@
     "bound_crs": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["BoundCRS"] },
         "source_crs": { "$ref": "#/definitions/crs" },
         "target_crs": { "$ref": "#/definitions/crs" },
@@ -128,6 +132,7 @@
            "type": "array",
             "items": { "$ref": "#/definitions/crs" }
         },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -151,6 +156,7 @@
            "type": "array",
             "items": { "$ref": "#/definitions/single_operation" }
         },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -165,6 +171,7 @@
     "conversion": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["Conversion"] },
         "name": { "type": "string" },
         "method": { "$ref": "#/definitions/method" },
@@ -185,6 +192,7 @@
     "coordinate_system": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["CoordinateSystem"] },
         "name": { "type": "string" },
         "subtype": { "type": "string",
@@ -245,6 +253,7 @@
     "datum_ensemble": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["DatumEnsemble"] },
         "name": { "type": "string" },
         "members": {
@@ -285,6 +294,7 @@
         "base_crs": { "$ref": "#/definitions/engineering_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -307,6 +317,7 @@
         "base_crs": { "$ref": "#/definitions/geodetic_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -328,6 +339,7 @@
         "base_crs": { "$ref": "#/definitions/parametric_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -349,6 +361,7 @@
         "base_crs": { "$ref": "#/definitions/projected_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -370,6 +383,7 @@
         "base_crs": { "$ref": "#/definitions/temporal_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -391,6 +405,7 @@
         "base_crs": { "$ref": "#/definitions/vertical_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -413,6 +428,7 @@
         "prime_meridian": {},
         "frame_reference_epoch": { "type": "number" },
         "deformation_model": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -433,6 +449,7 @@
         "anchor": {},
         "frame_reference_epoch": { "type": "number" },
         "deformation_model": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -449,6 +466,7 @@
       "oneOf":[
         {
           "properties": {
+            "$schema" : { "type": "string" },
             "type": { "type": "string", "enum": ["Ellipsoid"] },
             "name": { "type": "string" },
             "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
@@ -461,6 +479,7 @@
         },
         {
           "properties": {
+            "$schema" : { "type": "string" },
             "type": { "type": "string", "enum": ["Ellipsoid"] },
             "name": { "type": "string" },
             "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
@@ -473,6 +492,7 @@
         },
         {
           "properties": {
+            "$schema" : { "type": "string" },
             "type": { "type": "string", "enum": ["Ellipsoid"] },
             "name": { "type": "string" },
             "radius": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
@@ -496,6 +516,7 @@
         "name": { "type": "string" },
         "datum": { "$ref": "#/definitions/engineering_datum" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -514,6 +535,7 @@
         "type": { "type": "string", "enum": ["EngineeringDatum"] },
         "name": { "type": "string" },
         "anchor": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -538,6 +560,7 @@
         },
         "datum_ensemble": { "$ref": "#/definitions/datum_ensemble" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -563,6 +586,7 @@
         "anchor": { "type": "string" },
         "ellipsoid": { "$ref": "#/definitions/ellipsoid" },
         "prime_meridian": { "$ref": "#/definitions/prime_meridian" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -594,6 +618,7 @@
     "method": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["OperationMethod"]},
         "name": { "type": "string" },
         "id": { "$ref": "#/definitions/id" },
@@ -635,6 +660,7 @@
       {
         "type": "object",
         "properties": {
+            "$schema" : { "type": "string" },
             "scope": { "type": "string" },
             "area": { "type": "string" },
             "bbox": { "$ref": "#/definitions/bbox" },
@@ -649,6 +675,7 @@
       {
         "type": "object",
         "properties": {
+            "$schema" : { "type": "string" },
             "usages": { "$ref": "#/definitions/usages" },
             "remarks": { "type": "string" },
             "id": { "$ref": "#/definitions/id" },
@@ -664,6 +691,7 @@
     "parameter_value": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["ParameterValue"] },
         "name": { "type": "string" },
         "value": {
@@ -691,6 +719,7 @@
         "name": { "type": "string" },
         "datum": { "$ref": "#/definitions/parametric_datum" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -709,6 +738,7 @@
         "type": { "type": "string", "enum": ["ParametricDatum"] },
         "name": { "type": "string" },
         "anchor": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -723,6 +753,7 @@
     "prime_meridian": {
       "type": "object",
       "properties": {
+        "$schema" : { "type": "string" },
         "type": { "type": "string", "enum": ["PrimeMeridian"] },
         "name": { "type": "string" },
         "longitude": { "$ref": "#/definitions/value_and_unit" },
@@ -753,6 +784,7 @@
         "base_crs": { "$ref": "#/definitions/geodetic_crs" },
         "conversion": { "$ref": "#/definitions/conversion" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -772,6 +804,7 @@
         "name": { "type": "string" },
         "datum": { "$ref": "#/definitions/temporal_datum" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -791,6 +824,7 @@
         "name": { "type": "string" },
         "calendar": { "type": "string" },
         "time_origin": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -817,6 +851,7 @@
             "items": { "$ref": "#/definitions/parameter_value" }
         },
         "accuracy": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -897,6 +932,7 @@
         },
         "datum_ensemble": { "$ref": "#/definitions/datum_ensemble" },
         "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
@@ -920,6 +956,7 @@
         "type": { "type": "string", "enum": ["VerticalReferenceFrame"] },
         "name": { "type": "string" },
         "anchor": { "type": "string" },
+        "$schema" : {},
         "scope": {},
         "area": {},
         "bbox": {},
diff --git a/docs/Makefile b/docs/Makefile
index 4e1e88aa..c0801a9b 100644
--- a/docs/Makefile
+++ b/docs/Makefile
@@ -65,6 +65,7 @@ html: .doxygen_up_to_date
 	# Undoes the hacks of scripts/generate_breathe_friendly_general_doc.py
 	@sed "s/<em class=\"property\">namespace <\/em>//g" < $(BUILDDIR)/html/development/reference/cpp/cpp_general.html > $(BUILDDIR)/html/development/reference/cpp/cpp_general.html.tmp
 	@mv $(BUILDDIR)/html/development/reference/cpp/cpp_general.html.tmp $(BUILDDIR)/html/development/reference/cpp/cpp_general.html
+	@cp -r ../schemas $(BUILDDIR)/html/schemas
 	@echo
 	@echo "Build finished. The HTML pages are in $(BUILDDIR)/html."
 
diff --git a/docs/source/apps/projinfo.rst b/docs/source/apps/projinfo.rst
index efbc3948..8018f300 100644
--- a/docs/source/apps/projinfo.rst
+++ b/docs/source/apps/projinfo.rst
@@ -44,7 +44,7 @@ Synopsis
       (*added in 6.2*)
     - a OGC URN combining references for concatenated operations
       (e.g. "urn:ogc:def:coordinateOperation,coordinateOperation:EPSG::3895,coordinateOperation:EPSG::1618")
-    - a PROJJSON string. The jsonschema is at https://github.com/OSGeo/proj/blob/master/data/crsjson.schema.json (*added in 6.2*)
+    - a PROJJSON string. The jsonschema is at https://proj.org/schemas/v0.1/projjson.schema.json (*added in 6.2*)
 
     {object_reference} is a filename preceded by the '@' character.  The
     file referenced by the {object_reference} must contain a valid
diff --git a/include/proj/io.hpp b/include/proj/io.hpp
index 66c1a4cd..9c99fc0e 100644
--- a/include/proj/io.hpp
+++ b/include/proj/io.hpp
@@ -477,6 +477,7 @@ class PROJ_GCC_DLL JSONFormatter {
 
     PROJ_DLL JSONFormatter &setMultiLine(bool multiLine) noexcept;
     PROJ_DLL JSONFormatter &setIndentationWidth(int width) noexcept;
+    PROJ_DLL JSONFormatter &setSchema(const std::string &schema) noexcept;
 
     PROJ_DLL const std::string &toString() const;
 
diff --git a/schemas/v0.1/projjson.schema.json b/schemas/v0.1/projjson.schema.json
new file mode 100644
index 00000000..60fca6df
--- /dev/null
+++ b/schemas/v0.1/projjson.schema.json
@@ -0,0 +1,972 @@
+{
+  "$id": "https://proj.org/schemas/v0.1/projjson.schema.json",
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "description": "Schema for PROJJSON",
+  "$comment": "This file exists both in data/ and in schemas/vXXX/. Keep both in sync. And if changing the value of $id, change PROJJSON_CURRENT_VERSION accordingly in io.cpp",
+
+  "oneOf": [
+    { "$ref": "#/definitions/crs" },
+    { "$ref": "#/definitions/datum" },
+    { "$ref": "#/definitions/datum_ensemble" },
+    { "$ref": "#/definitions/ellipsoid" },
+    { "$ref": "#/definitions/prime_meridian" },
+    { "$ref": "#/definitions/single_operation" },
+    { "$ref": "#/definitions/concatenated_operation" }
+  ],
+
+  "definitions": {
+
+    "abridged_transformation": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["AbridgedTransformation"] },
+        "name": { "type": "string" },
+        "method": { "$ref": "#/definitions/method" },
+        "parameters": {
+            "type": "array",
+            "items": { "$ref": "#/definitions/parameter_value" }
+        },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name", "method", "parameters" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "axis": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["Axis"] },
+        "name": { "type": "string" },
+        "abbreviation": { "type": "string" },
+        "direction": { "type": "string",
+                       "enum": [ "north",
+                                 "northNorthEast",
+                                 "northEast",
+                                 "eastNorthEast",
+                                 "east",
+                                 "eastSouthEast",
+                                 "southEast",
+                                 "southSouthEast",
+                                 "south",
+                                 "southSouthWest",
+                                 "southWest",
+                                 "westSouthWest",
+                                 "west",
+                                 "westNorthWest",
+                                 "northWest",
+                                 "northNorthWest",
+                                 "up",
+                                 "down",
+                                 "geocentricX",
+                                 "geocentricY",
+                                 "geocentricZ",
+                                 "columnPositive",
+                                 "columnNegative",
+                                 "rowPositive",
+                                 "rowNegative",
+                                 "displayRight",
+                                 "displayLeft",
+                                 "displayUp",
+                                 "displayDown",
+                                 "forward",
+                                 "aft",
+                                 "port",
+                                 "starboard",
+                                 "clockwise",
+                                 "counterClockwise",
+                                 "towards",
+                                 "awayFrom",
+                                 "future",
+                                 "past",
+                                 "unspecified" ] },
+        "unit": { "$ref": "#/definitions/unit" },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name", "abbreviation", "direction" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "bbox": {
+      "type": "object",
+      "properties": {
+        "east_longitude": { "type": "number" },
+        "west_longitude": { "type": "number" },
+        "south_latitude": { "type": "number" },
+        "north_latitude": { "type": "number" }
+      },
+      "required" : [ "east_longitude", "west_longitude",
+                     "south_latitude", "north_latitude" ],
+      "additionalProperties": false
+    },
+
+    "bound_crs": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["BoundCRS"] },
+        "source_crs": { "$ref": "#/definitions/crs" },
+        "target_crs": { "$ref": "#/definitions/crs" },
+        "transformation": { "$ref": "#/definitions/abridged_transformation" }
+     },
+     "required" : [ "source_crs", "target_crs", "transformation" ],
+     "additionalProperties": false
+    },
+
+    "compound_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["CompoundCRS"] },
+        "name": { "type": "string" },
+        "components":  {
+           "type": "array",
+            "items": { "$ref": "#/definitions/crs" }
+        },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "components" ],
+      "additionalProperties": false
+    },
+
+    "concatenated_operation": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["ConcatenatedOperation"] },
+        "name": { "type": "string" },
+        "source_crs": { "$ref": "#/definitions/crs" },
+        "target_crs": { "$ref": "#/definitions/crs" },
+        "steps":  {
+           "type": "array",
+            "items": { "$ref": "#/definitions/single_operation" }
+        },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "source_crs", "target_crs", "steps" ],
+      "additionalProperties": false
+    },
+
+    "conversion": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["Conversion"] },
+        "name": { "type": "string" },
+        "method": { "$ref": "#/definitions/method" },
+        "parameters": {
+            "type": "array",
+            "items": { "$ref": "#/definitions/parameter_value" }
+        },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name", "method" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "coordinate_system": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["CoordinateSystem"] },
+        "name": { "type": "string" },
+        "subtype": { "type": "string",
+                     "enum": ["Cartesian",
+                              "spherical",
+                              "ellipsoidal",
+                              "vertical",
+                              "ordinal",
+                              "parametric",
+                              "TemporalDateTime",
+                              "TemporalCount",
+                              "TemporalMeasure"]  },
+        "axis": {
+            "type": "array",
+            "items": { "$ref": "#/definitions/axis" }
+        },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "subtype", "axis" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "crs": {
+      "oneOf": [
+        { "$ref": "#/definitions/bound_crs" },
+        { "$ref": "#/definitions/compound_crs" },
+        { "$ref": "#/definitions/derived_engineering_crs" },
+        { "$ref": "#/definitions/derived_geodetic_crs" },
+        { "$ref": "#/definitions/derived_parametric_crs" },
+        { "$ref": "#/definitions/derived_projected_crs" },
+        { "$ref": "#/definitions/derived_temporal_crs" },
+        { "$ref": "#/definitions/derived_vertical_crs" },
+        { "$ref": "#/definitions/engineering_crs" },
+        { "$ref": "#/definitions/geodetic_crs" },
+        { "$ref": "#/definitions/parametric_crs" },
+        { "$ref": "#/definitions/projected_crs" },
+        { "$ref": "#/definitions/temporal_crs" },
+        { "$ref": "#/definitions/vertical_crs" }
+      ]
+    },
+
+    "datum": {
+      "oneOf": [
+        { "$ref": "#/definitions/geodetic_reference_frame" },
+        { "$ref": "#/definitions/vertical_reference_frame" },
+        { "$ref": "#/definitions/dynamic_geodetic_reference_frame" },
+        { "$ref": "#/definitions/dynamic_vertical_reference_frame" },
+        { "$ref": "#/definitions/temporal_datum" },
+        { "$ref": "#/definitions/parametric_datum" },
+        { "$ref": "#/definitions/engineering_datum" }
+      ]
+    },
+
+    "datum_ensemble": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["DatumEnsemble"] },
+        "name": { "type": "string" },
+        "members": {
+            "type": "array",
+            "items": {
+                "type": "object",
+                "properties": {
+                    "name": { "type": "string" },
+                    "id": { "$ref": "#/definitions/id" },
+                    "ids": { "$ref": "#/definitions/ids" }
+                },
+                "required" : [ "name" ],
+                "allOf": [
+                    { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+                ],
+                "additionalProperties": false
+            }
+        },
+        "ellipsoid": { "$ref": "#/definitions/ellipsoid" },
+        "accuracy": { "type": "string" },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name", "members", "accuracy" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "derived_engineering_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["DerivedEngineeringCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/engineering_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "derived_geodetic_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["DerivedGeodeticCRS",
+                           "DerivedGeographicCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/geodetic_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "derived_parametric_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["DerivedParametricCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/parametric_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "derived_projected_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["DerivedProjectedCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/projected_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "derived_temporal_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["DerivedTemporalCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/temporal_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "derived_vertical_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["DerivedVerticalCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/vertical_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "dynamic_geodetic_reference_frame": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/geodetic_reference_frame" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["DynamicGeodeticReferenceFrame"] },
+        "name": {},
+        "anchor": {},
+        "ellipsoid": {},
+        "prime_meridian": {},
+        "frame_reference_epoch": { "type": "number" },
+        "deformation_model": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "ellipsoid", "frame_reference_epoch" ],
+      "additionalProperties": false
+    },
+
+    "dynamic_vertical_reference_frame": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/vertical_reference_frame" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["DynamicVerticalReferenceFrame"] },
+        "name": {},
+        "anchor": {},
+        "frame_reference_epoch": { "type": "number" },
+        "deformation_model": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "frame_reference_epoch" ],
+      "additionalProperties": false
+    },
+
+    "ellipsoid": {
+      "type": "object",
+      "oneOf":[
+        {
+          "properties": {
+            "$schema" : { "type": "string" },
+            "type": { "type": "string", "enum": ["Ellipsoid"] },
+            "name": { "type": "string" },
+            "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
+            "semi_minor_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
+            "id": { "$ref": "#/definitions/id" },
+            "ids": { "$ref": "#/definitions/ids" }
+          },
+          "required" : [ "name", "semi_major_axis", "semi_minor_axis" ],
+          "additionalProperties": false
+        },
+        {
+          "properties": {
+            "$schema" : { "type": "string" },
+            "type": { "type": "string", "enum": ["Ellipsoid"] },
+            "name": { "type": "string" },
+            "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
+            "inverse_flattening": { "type": "number" },
+            "id": { "$ref": "#/definitions/id" },
+           "ids": { "$ref": "#/definitions/ids" }
+          },
+          "required" : [ "name", "semi_major_axis", "inverse_flattening" ],
+          "additionalProperties": false
+        },
+        {
+          "properties": {
+            "$schema" : { "type": "string" },
+            "type": { "type": "string", "enum": ["Ellipsoid"] },
+            "name": { "type": "string" },
+            "radius": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
+            "id": { "$ref": "#/definitions/id" },
+            "ids": { "$ref": "#/definitions/ids" }
+          },
+          "required" : [ "name", "radius" ],
+         "additionalProperties": false
+        }
+      ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ]
+    },
+
+    "engineering_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["EngineeringCRS"] },
+        "name": { "type": "string" },
+        "datum": { "$ref": "#/definitions/engineering_datum" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "datum" ],
+      "additionalProperties": false
+    },
+
+    "engineering_datum": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["EngineeringDatum"] },
+        "name": { "type": "string" },
+        "anchor": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name" ],
+      "additionalProperties": false
+    },
+
+    "geodetic_crs": {
+      "type": "object",
+      "properties": {
+        "type": { "type": "string", "enum": ["GeodeticCRS", "GeographicCRS"] },
+        "name": { "type": "string" },
+        "datum": {
+            "oneOf": [
+                { "$ref": "#/definitions/geodetic_reference_frame" },
+                { "$ref": "#/definitions/dynamic_geodetic_reference_frame" }
+            ]
+        },
+        "datum_ensemble": { "$ref": "#/definitions/datum_ensemble" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name" ],
+      "description": "One and only one of datum and datum_ensemble must be provided",
+      "allOf": [
+        { "$ref": "#/definitions/object_usage" },
+        { "$ref": "#/definitions/one_and_only_one_of_datum_or_datum_ensemble" }
+      ],
+      "additionalProperties": false
+    },
+
+    "geodetic_reference_frame": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["GeodeticReferenceFrame"] },
+        "name": { "type": "string" },
+        "anchor": { "type": "string" },
+        "ellipsoid": { "$ref": "#/definitions/ellipsoid" },
+        "prime_meridian": { "$ref": "#/definitions/prime_meridian" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "ellipsoid" ],
+      "additionalProperties": false
+    },
+
+    "id": {
+      "type": "object",
+      "properties": {
+        "authority": { "type": "string" },
+        "code": {
+          "oneOf": [ { "type": "string" }, { "type": "integer" } ]
+        }
+      },
+      "required" : [ "authority", "code" ],
+      "additionalProperties": false
+    },
+
+    "ids": {
+      "type": "array",
+      "items": { "$ref": "#/definitions/id" }
+    },
+
+    "method": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["OperationMethod"]},
+        "name": { "type": "string" },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "id_ids_mutually_exclusive": {
+        "not": {
+            "type": "object",
+            "required": [ "id", "ids" ]
+        }
+    },
+
+    "one_and_only_one_of_datum_or_datum_ensemble": {
+      "allOf": [
+        {
+            "not": {
+                "type": "object",
+                "required": [ "datum", "datum_ensemble" ]
+            }
+        },
+        {
+            "oneOf": [
+                { "type": "object", "required": ["datum"] },
+                { "type": "object", "required": ["datum_ensemble"] }
+            ]
+        }
+      ]
+    },
+
+    "object_usage": {
+      "anyOf": [
+      {
+        "type": "object",
+        "properties": {
+            "$schema" : { "type": "string" },
+            "scope": { "type": "string" },
+            "area": { "type": "string" },
+            "bbox": { "$ref": "#/definitions/bbox" },
+            "remarks": { "type": "string" },
+            "id": { "$ref": "#/definitions/id" },
+            "ids": { "$ref": "#/definitions/ids" }
+        },
+        "allOf": [
+            { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+        ]
+      },
+      {
+        "type": "object",
+        "properties": {
+            "$schema" : { "type": "string" },
+            "usages": { "$ref": "#/definitions/usages" },
+            "remarks": { "type": "string" },
+            "id": { "$ref": "#/definitions/id" },
+            "ids": { "$ref": "#/definitions/ids" }
+        },
+        "allOf": [
+            { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+        ]
+      }
+      ]
+    },
+
+    "parameter_value": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["ParameterValue"] },
+        "name": { "type": "string" },
+        "value": {
+          "oneOf": [
+            { "type": "string" },
+            { "type": "number" }
+           ]
+        },
+        "unit": { "$ref": "#/definitions/unit" },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name", "value" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "parametric_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["ParametricCRS"] },
+        "name": { "type": "string" },
+        "datum": { "$ref": "#/definitions/parametric_datum" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "datum" ],
+      "additionalProperties": false
+    },
+
+    "parametric_datum": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["ParametricDatum"] },
+        "name": { "type": "string" },
+        "anchor": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name" ],
+      "additionalProperties": false
+    },
+
+    "prime_meridian": {
+      "type": "object",
+      "properties": {
+        "$schema" : { "type": "string" },
+        "type": { "type": "string", "enum": ["PrimeMeridian"] },
+        "name": { "type": "string" },
+        "longitude": { "$ref": "#/definitions/value_and_unit" },
+        "id": { "$ref": "#/definitions/id" },
+        "ids": { "$ref": "#/definitions/ids" }
+      },
+      "required" : [ "name" ],
+      "allOf": [
+        { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+      ],
+      "additionalProperties": false
+    },
+
+    "single_operation": {
+      "oneOf": [
+        { "$ref": "#/definitions/conversion" },
+        { "$ref": "#/definitions/transformation" }
+      ]
+    },
+
+    "projected_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string",
+                  "enum": ["ProjectedCRS"] },
+        "name": { "type": "string" },
+        "base_crs": { "$ref": "#/definitions/geodetic_crs" },
+        "conversion": { "$ref": "#/definitions/conversion" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+     },
+     "required" : [ "name", "base_crs", "conversion", "coordinate_system" ],
+     "additionalProperties": false
+    },
+
+    "temporal_crs": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["TemporalCRS"] },
+        "name": { "type": "string" },
+        "datum": { "$ref": "#/definitions/temporal_datum" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "datum" ],
+      "additionalProperties": false
+    },
+
+    "temporal_datum": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["TemporalDatum"] },
+        "name": { "type": "string" },
+        "calendar": { "type": "string" },
+        "time_origin": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "calendar" ],
+      "additionalProperties": false
+    },
+
+    "transformation": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["Transformation"] },
+        "name": { "type": "string" },
+        "source_crs": { "$ref": "#/definitions/crs" },
+        "target_crs": { "$ref": "#/definitions/crs" },
+        "interpolation_crs": { "$ref": "#/definitions/crs" },
+        "method": { "$ref": "#/definitions/method" },
+        "parameters": {
+            "type": "array",
+            "items": { "$ref": "#/definitions/parameter_value" }
+        },
+        "accuracy": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name", "source_crs", "target_crs", "method", "parameters" ],
+      "additionalProperties": false
+    },
+
+    "unit": {
+      "oneOf": [
+      {
+        "type": "string",
+        "enum": ["metre", "degree", "unity"]
+      },
+      {
+        "type": "object",
+        "properties": {
+          "type": { "type": "string",
+                    "enum": ["LinearUnit", "AngularUnit", "ScaleUnit",
+                             "TimeUnit", "ParametricUnit", "Unit"] },
+          "name": { "type": "string" },
+          "conversion_factor": { "type": "number" },
+          "id": { "$ref": "#/definitions/id" },
+          "ids": { "$ref": "#/definitions/ids" }
+         },
+         "required" : [ "type", "name" ],
+         "allOf": [
+            { "$ref": "#/definitions/id_ids_mutually_exclusive" }
+          ],
+         "additionalProperties": false
+      }
+      ]
+    },
+
+    "usages": {
+        "type": "array",
+        "items": {
+          "type": "object",
+          "properties": {
+            "scope": { "type": "string" },
+            "area": { "type": "string" },
+            "bbox": { "$ref": "#/definitions/bbox" }
+           },
+          "additionalProperties": false
+        }
+    },
+
+    "value_and_unit": {
+      "type": "object",
+      "properties": {
+        "value": { "type": "number" },
+        "unit": { "$ref": "#/definitions/unit" }
+      },
+      "required" : [ "value", "unit" ],
+      "additionalProperties": false
+    },
+
+    "value_in_metre_or_value_and_unit": {
+      "oneOf": [
+        { "type": "number" },
+        { "$ref": "#/definitions/value_and_unit" }
+      ]
+    },
+
+    "vertical_crs": {
+      "type": "object",
+      "properties": {
+        "type": { "type": "string", "enum": ["VerticalCRS"] },
+        "name": { "type": "string" },
+        "datum": {
+            "oneOf": [
+                { "$ref": "#/definitions/vertical_reference_frame" },
+                { "$ref": "#/definitions/dynamic_vertical_reference_frame" }
+            ]
+        },
+        "datum_ensemble": { "$ref": "#/definitions/datum_ensemble" },
+        "coordinate_system": { "$ref": "#/definitions/coordinate_system" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name"],
+      "description": "One and only one of datum and datum_ensemble must be provided",
+      "allOf": [
+        { "$ref": "#/definitions/object_usage" },
+        { "$ref": "#/definitions/one_and_only_one_of_datum_or_datum_ensemble" }
+      ],
+      "additionalProperties": false
+    },
+
+    "vertical_reference_frame": {
+      "type": "object",
+      "allOf": [{ "$ref": "#/definitions/object_usage" }],
+      "properties": {
+        "type": { "type": "string", "enum": ["VerticalReferenceFrame"] },
+        "name": { "type": "string" },
+        "anchor": { "type": "string" },
+        "$schema" : {},
+        "scope": {},
+        "area": {},
+        "bbox": {},
+        "usages": {},
+        "remarks": {},
+        "id": {}, "ids": {}
+      },
+      "required" : [ "name" ],
+      "additionalProperties": false
+    }
+
+  }
+}
diff --git a/scripts/reference_exported_symbols.txt b/scripts/reference_exported_symbols.txt
index a372d163..a453bb2d 100644
--- a/scripts/reference_exported_symbols.txt
+++ b/scripts/reference_exported_symbols.txt
@@ -344,6 +344,7 @@ osgeo::proj::io::JSONFormatter::ObjectContext::~ObjectContext()
 osgeo::proj::io::JSONFormatter::ObjectContext::ObjectContext(osgeo::proj::io::JSONFormatter&, char const*, bool)
 osgeo::proj::io::JSONFormatter::setIndentationWidth(int)
 osgeo::proj::io::JSONFormatter::setMultiLine(bool)
+osgeo::proj::io::JSONFormatter::setSchema(std::string const&)
 osgeo::proj::io::JSONFormatter::toString() const
 osgeo::proj::io::NoSuchAuthorityCodeException::getAuthorityCode() const
 osgeo::proj::io::NoSuchAuthorityCodeException::getAuthority() const
diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index d4813091..d27b8800 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -1335,6 +1335,8 @@ const char *proj_as_proj_string(PJ_CONTEXT *ctx, const PJ *obj,
  * <li>MULTILINE=YES/NO. Defaults to YES</li>
  * <li>INDENTATION_WIDTH=number. Defauls to 2 (when multiline output is
  * on).</li>
+ * <li>SCHEMA=string. URL to PROJJSON schema. Can be set to empty string to
+ * disable it.</li>
  * </ul>
  * @return a string, or NULL in case of error.
  *
@@ -1359,6 +1361,8 @@ const char *proj_as_projjson(PJ_CONTEXT *ctx, const PJ *obj,
                 formatter->setMultiLine(ci_equal(value, "YES"));
             } else if ((value = getOptionValue(*iter, "INDENTATION_WIDTH="))) {
                 formatter->setIndentationWidth(std::atoi(value));
+            } else if ((value = getOptionValue(*iter, "SCHEMA="))) {
+                formatter->setSchema(value);
             } else {
                 std::string msg("Unknown option :");
                 msg += *iter;
diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index 9f4f6061..5ccd9642 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -86,6 +86,10 @@ using json = nlohmann::json;
 
 //! @cond Doxygen_Suppress
 static const std::string emptyString{};
+
+// If changing that value, change it in data/projjson.schema.json as well
+#define PROJJSON_CURRENT_VERSION                                               \
+    "https://proj.org/schemas/v0.1/projjson.schema.json"
 //! @endcond
 
 #if 0
@@ -9103,6 +9107,7 @@ struct JSONFormatter::Private {
     bool allowIDInImmediateChild_ = false;
     bool omitTypeInImmediateChild_ = false;
     bool abridgedTransformation_ = false;
+    std::string schema_ = PROJJSON_CURRENT_VERSION;
 
     std::string result_{};
 
@@ -9148,6 +9153,17 @@ JSONFormatter &JSONFormatter::setIndentationWidth(int width) noexcept {
 
 // ---------------------------------------------------------------------------
 
+/** \brief Set the value of the "$schema" key in the top level object.
+ *
+ * If set to empty string, it will not be written.
+ */
+JSONFormatter &JSONFormatter::setSchema(const std::string &schema) noexcept {
+    d->schema_ = schema;
+    return *this;
+}
+
+// ---------------------------------------------------------------------------
+
 //! @cond Doxygen_Suppress
 
 JSONFormatter::JSONFormatter() : d(internal::make_unique<Private>()) {}
@@ -9188,6 +9204,11 @@ JSONFormatter::ObjectContext::ObjectContext(JSONFormatter &formatter,
                                             const char *objectType, bool hasId)
     : m_formatter(formatter) {
     m_formatter.d->writer_.StartObj();
+    if (m_formatter.d->outputIdStack_.size() == 1 &&
+        !m_formatter.d->schema_.empty()) {
+        m_formatter.d->writer_.AddObjKey("$schema");
+        m_formatter.d->writer_.Add(m_formatter.d->schema_);
+    }
     if (objectType && !m_formatter.d->omitTypeInImmediateChild_) {
         m_formatter.d->writer_.AddObjKey("type");
         m_formatter.d->writer_.Add(objectType);
diff --git a/test/cli/testprojinfo_out.dist b/test/cli/testprojinfo_out.dist
index 73751b99..97c1138c 100644
--- a/test/cli/testprojinfo_out.dist
+++ b/test/cli/testprojinfo_out.dist
@@ -137,6 +137,7 @@ GEOGCS["GCS_WGS_1984",DATUM["D_WGS_1984",SPHEROID["WGS_1984",6378137.0,298.25722
 
 PROJJSON:
 {
+  "$schema": "https://proj.org/schemas/v0.1/projjson.schema.json",
   "type": "GeographicCRS",
   "name": "WGS 84",
   "datum": {
diff --git a/test/unit/test_c_api.cpp b/test/unit/test_c_api.cpp
index 5649ca9f..97440796 100644
--- a/test/unit/test_c_api.cpp
+++ b/test/unit/test_c_api.cpp
@@ -3503,6 +3503,8 @@ TEST_F(CApi, proj_as_projjson) {
         ASSERT_NE(projjson, nullptr);
         EXPECT_EQ(std::string(projjson),
                   "{\n"
+                  "  \"$schema\": "
+                  "\"https://proj.org/schemas/v0.1/projjson.schema.json\",\n"
                   "  \"type\": \"Ellipsoid\",\n"
                   "  \"name\": \"WGS 84\",\n"
                   "  \"semi_major_axis\": 6378137,\n"
@@ -3514,7 +3516,8 @@ TEST_F(CApi, proj_as_projjson) {
                   "}");
     }
     {
-        const char *const options[] = {"INDENTATION_WIDTH=4", nullptr};
+        const char *const options[] = {"INDENTATION_WIDTH=4", "SCHEMA=",
+                                       nullptr};
         auto projjson = proj_as_projjson(m_ctxt, obj, options);
         ASSERT_NE(projjson, nullptr);
         EXPECT_EQ(std::string(projjson),
@@ -3530,7 +3533,7 @@ TEST_F(CApi, proj_as_projjson) {
                   "}");
     }
     {
-        const char *const options[] = {"MULTILINE=NO", nullptr};
+        const char *const options[] = {"MULTILINE=NO", "SCHEMA=", nullptr};
         auto projjson = proj_as_projjson(m_ctxt, obj, options);
         ASSERT_NE(projjson, nullptr);
         EXPECT_EQ(std::string(projjson),
diff --git a/test/unit/test_datum.cpp b/test/unit/test_datum.cpp
index d8fab1f0..fbd1f79d 100644
--- a/test/unit/test_datum.cpp
+++ b/test/unit/test_datum.cpp
@@ -207,19 +207,20 @@ TEST(datum, prime_meridian_to_PROJString) {
 
 TEST(datum, prime_meridian_to_JSON) {
 
-    EXPECT_EQ(
-        PrimeMeridian::GREENWICH->exportToJSON(JSONFormatter::create().get()),
-        "{\n"
-        "  \"type\": \"PrimeMeridian\",\n"
-        "  \"name\": \"Greenwich\",\n"
-        "  \"longitude\": 0,\n"
-        "  \"id\": {\n"
-        "    \"authority\": \"EPSG\",\n"
-        "    \"code\": 8901\n"
-        "  }\n"
-        "}");
-
-    EXPECT_EQ(PrimeMeridian::PARIS->exportToJSON(JSONFormatter::create().get()),
+    EXPECT_EQ(PrimeMeridian::GREENWICH->exportToJSON(
+                  &(JSONFormatter::create()->setSchema(""))),
+              "{\n"
+              "  \"type\": \"PrimeMeridian\",\n"
+              "  \"name\": \"Greenwich\",\n"
+              "  \"longitude\": 0,\n"
+              "  \"id\": {\n"
+              "    \"authority\": \"EPSG\",\n"
+              "    \"code\": 8901\n"
+              "  }\n"
+              "}");
+
+    EXPECT_EQ(PrimeMeridian::PARIS->exportToJSON(
+                  &(JSONFormatter::create()->setSchema(""))),
               "{\n"
               "  \"type\": \"PrimeMeridian\",\n"
               "  \"name\": \"Paris\",\n"
diff --git a/test/unit/test_io.cpp b/test/unit/test_io.cpp
index e1d424e9..7a3e6729 100644
--- a/test/unit/test_io.cpp
+++ b/test/unit/test_io.cpp
@@ -9137,6 +9137,7 @@ TEST(wkt_export, invalid_angular_unit) {
 
 TEST(json_import, ellipsoid_flattened_sphere) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"Ellipsoid\",\n"
                 "  \"name\": \"WGS 84\",\n"
                 "  \"semi_major_axis\": 6378137,\n"
@@ -9149,13 +9150,15 @@ TEST(json_import, ellipsoid_flattened_sphere) {
     auto obj = createFromUserInput(json, nullptr);
     auto ellps = nn_dynamic_pointer_cast<Ellipsoid>(obj);
     ASSERT_TRUE(ellps != nullptr);
-    EXPECT_EQ(ellps->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(ellps->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, ellipsoid_major_minor_custom_unit) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"Ellipsoid\",\n"
                 "  \"name\": \"foo\",\n"
                 "  \"semi_major_axis\": 6378137,\n"
@@ -9171,13 +9174,15 @@ TEST(json_import, ellipsoid_major_minor_custom_unit) {
     auto obj = createFromUserInput(json, nullptr);
     auto ellps = nn_dynamic_pointer_cast<Ellipsoid>(obj);
     ASSERT_TRUE(ellps != nullptr);
-    EXPECT_EQ(ellps->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(ellps->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, ellipsoid_sphere) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"Ellipsoid\",\n"
                 "  \"name\": \"Sphere\",\n"
                 "  \"radius\": 6371000,\n"
@@ -9189,7 +9194,8 @@ TEST(json_import, ellipsoid_sphere) {
     auto obj = createFromUserInput(json, nullptr);
     auto ellps = nn_dynamic_pointer_cast<Ellipsoid>(obj);
     ASSERT_TRUE(ellps != nullptr);
-    EXPECT_EQ(ellps->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(ellps->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
@@ -9217,6 +9223,7 @@ TEST(json_import, ellipsoid_errors) {
 
 TEST(json_import, prime_meridian) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"PrimeMeridian\",\n"
                 "  \"name\": \"Paris\",\n"
                 "  \"longitude\": {\n"
@@ -9231,7 +9238,8 @@ TEST(json_import, prime_meridian) {
     auto obj = createFromUserInput(json, nullptr);
     auto pm = nn_dynamic_pointer_cast<PrimeMeridian>(obj);
     ASSERT_TRUE(pm != nullptr);
-    EXPECT_EQ(pm->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(pm->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
@@ -9251,6 +9259,7 @@ TEST(json_import, prime_meridian_errors) {
 
 TEST(json_import, geodetic_reference_frame_with_implicit_prime_meridian) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"GeodeticReferenceFrame\",\n"
                 "  \"name\": \"World Geodetic System 1984\",\n"
                 "  \"ellipsoid\": {\n"
@@ -9262,13 +9271,15 @@ TEST(json_import, geodetic_reference_frame_with_implicit_prime_meridian) {
     auto obj = createFromUserInput(json, nullptr);
     auto grf = nn_dynamic_pointer_cast<GeodeticReferenceFrame>(obj);
     ASSERT_TRUE(grf != nullptr);
-    EXPECT_EQ(grf->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(grf->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, geodetic_reference_frame_with_explicit_prime_meridian) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"GeodeticReferenceFrame\",\n"
                 "  \"name\": \"Nouvelle Triangulation Francaise (Paris)\",\n"
                 "  \"ellipsoid\": {\n"
@@ -9291,7 +9302,8 @@ TEST(json_import, geodetic_reference_frame_with_explicit_prime_meridian) {
     auto obj = createFromUserInput(json, nullptr);
     auto grf = nn_dynamic_pointer_cast<GeodeticReferenceFrame>(obj);
     ASSERT_TRUE(grf != nullptr);
-    EXPECT_EQ(grf->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(grf->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
@@ -9299,6 +9311,7 @@ TEST(json_import, geodetic_reference_frame_with_explicit_prime_meridian) {
 TEST(json_import,
      dynamic_geodetic_reference_frame_with_implicit_prime_meridian) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DynamicGeodeticReferenceFrame\",\n"
                 "  \"name\": \"World Geodetic System 1984\",\n"
                 "  \"frame_reference_epoch\": 1,\n"
@@ -9312,7 +9325,8 @@ TEST(json_import,
     auto obj = createFromUserInput(json, nullptr);
     auto dgrf = nn_dynamic_pointer_cast<DynamicGeodeticReferenceFrame>(obj);
     ASSERT_TRUE(dgrf != nullptr);
-    EXPECT_EQ(dgrf->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(dgrf->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
@@ -9329,6 +9343,7 @@ TEST(json_import, geodetic_reference_frame_errors) {
 
 TEST(json_import, dynamic_vertical_reference_frame) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DynamicVerticalReferenceFrame\",\n"
                 "  \"name\": \"bar\",\n"
                 "  \"frame_reference_epoch\": 1,\n"
@@ -9337,13 +9352,15 @@ TEST(json_import, dynamic_vertical_reference_frame) {
     auto obj = createFromUserInput(json, nullptr);
     auto dvrf = nn_dynamic_pointer_cast<DynamicVerticalReferenceFrame>(obj);
     ASSERT_TRUE(dvrf != nullptr);
-    EXPECT_EQ(dvrf->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(dvrf->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, several_usages) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"GeodeticReferenceFrame\",\n"
                 "  \"name\": \"World Geodetic System 1984\",\n"
                 "  \"ellipsoid\": {\n"
@@ -9370,13 +9387,15 @@ TEST(json_import, several_usages) {
     auto obj = createFromUserInput(json, nullptr);
     auto gdr = nn_dynamic_pointer_cast<GeodeticReferenceFrame>(obj);
     ASSERT_TRUE(gdr != nullptr);
-    EXPECT_EQ(gdr->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(gdr->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, geographic_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"GeographicCRS\",\n"
                 "  \"name\": \"WGS 84\",\n"
                 "  \"datum\": {\n"
@@ -9421,7 +9440,8 @@ TEST(json_import, geographic_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto gcrs = nn_dynamic_pointer_cast<GeographicCRS>(obj);
     ASSERT_TRUE(gcrs != nullptr);
-    EXPECT_EQ(gcrs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(gcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
@@ -9486,6 +9506,7 @@ TEST(json_import, geographic_crs_errors) {
 
 TEST(json_import, geocentric_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"GeodeticCRS\",\n"
                 "  \"name\": \"WGS 84\",\n"
                 "  \"datum\": {\n"
@@ -9524,13 +9545,15 @@ TEST(json_import, geocentric_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto gdcrs = nn_dynamic_pointer_cast<GeodeticCRS>(obj);
     ASSERT_TRUE(gdcrs != nullptr);
-    EXPECT_EQ(gdcrs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(gdcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, projected_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"ProjectedCRS\",\n"
                 "  \"name\": \"WGS 84 / UTM zone 31N\",\n"
                 "  \"base_crs\": {\n"
@@ -9644,13 +9667,15 @@ TEST(json_import, projected_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto pcrs = nn_dynamic_pointer_cast<ProjectedCRS>(obj);
     ASSERT_TRUE(pcrs != nullptr);
-    EXPECT_EQ(pcrs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(pcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, compound_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"CompoundCRS\",\n"
                 "  \"name\": \"WGS 84 + EGM2008 height\",\n"
                 "  \"components\": [\n"
@@ -9716,7 +9741,9 @@ TEST(json_import, compound_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto compoundCRS = nn_dynamic_pointer_cast<CompoundCRS>(obj);
     ASSERT_TRUE(compoundCRS != nullptr);
-    EXPECT_EQ(compoundCRS->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(
+        compoundCRS->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+        json);
 }
 
 // ---------------------------------------------------------------------------
@@ -9724,6 +9751,7 @@ TEST(json_import, compound_crs) {
 TEST(json_import, bound_crs) {
     auto json =
         "{\n"
+        "  \"$schema\": \"foo\",\n"
         "  \"type\": \"BoundCRS\",\n"
         "  \"source_crs\": {\n"
         "    \"type\": \"GeographicCRS\",\n"
@@ -9817,13 +9845,16 @@ TEST(json_import, bound_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto boundCRS = nn_dynamic_pointer_cast<BoundCRS>(obj);
     ASSERT_TRUE(boundCRS != nullptr);
-    EXPECT_EQ(boundCRS->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(
+        boundCRS->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+        json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, transformation) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"Transformation\",\n"
                 "  \"name\": \"GDA94 to GDA2020 (1)\",\n"
                 "  \"source_crs\": {\n"
@@ -10004,7 +10035,9 @@ TEST(json_import, transformation) {
     auto obj = createFromUserInput(json, nullptr);
     auto transf = nn_dynamic_pointer_cast<Transformation>(obj);
     ASSERT_TRUE(transf != nullptr);
-    EXPECT_EQ(transf->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(
+        transf->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+        json);
 }
 
 // ---------------------------------------------------------------------------
@@ -10012,6 +10045,7 @@ TEST(json_import, transformation) {
 TEST(json_import, concatenated_operation) {
     auto json =
         "{\n"
+        "  \"$schema\": \"foo\",\n"
         "  \"type\": \"ConcatenatedOperation\",\n"
         "  \"name\": \"Inverse of Vicgrid + GDA94 to GDA2020 (1)\",\n"
         "  \"source_crs\": {\n"
@@ -10434,13 +10468,16 @@ TEST(json_import, concatenated_operation) {
     auto obj = createFromUserInput(json, nullptr);
     auto concat = nn_dynamic_pointer_cast<ConcatenatedOperation>(obj);
     ASSERT_TRUE(concat != nullptr);
-    EXPECT_EQ(concat->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(
+        concat->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+        json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, geographic_crs_with_datum_ensemble) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"GeographicCRS\",\n"
                 "  \"name\": \"WGS 84\",\n"
                 "  \"datum_ensemble\": {\n"
@@ -10481,6 +10518,7 @@ TEST(json_import, geographic_crs_with_datum_ensemble) {
 
     auto expected_json =
         "{\n"
+        "  \"$schema\": \"foo\",\n"
         "  \"type\": \"GeographicCRS\",\n"
         "  \"name\": \"WGS 84\",\n"
         "  \"datum_ensemble\": {\n"
@@ -10536,22 +10574,26 @@ TEST(json_import, geographic_crs_with_datum_ensemble) {
         auto obj = createFromUserInput(json, nullptr);
         auto gcrs = nn_dynamic_pointer_cast<GeographicCRS>(obj);
         ASSERT_TRUE(gcrs != nullptr);
-        EXPECT_EQ(gcrs->exportToJSON((JSONFormatter::create().get())), json);
+        EXPECT_EQ(
+            gcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+            json);
     }
     {
         auto obj = createFromUserInput(json, DatabaseContext::create());
         auto gcrs = nn_dynamic_pointer_cast<GeographicCRS>(obj);
         ASSERT_TRUE(gcrs != nullptr);
-        EXPECT_EQ(gcrs->exportToJSON((JSONFormatter::create().get())),
-                  expected_json);
+        EXPECT_EQ(
+            gcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+            expected_json);
     }
     {
         auto obj =
             createFromUserInput(expected_json, DatabaseContext::create());
         auto gcrs = nn_dynamic_pointer_cast<GeographicCRS>(obj);
         ASSERT_TRUE(gcrs != nullptr);
-        EXPECT_EQ(gcrs->exportToJSON((JSONFormatter::create().get())),
-                  expected_json);
+        EXPECT_EQ(
+            gcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+            expected_json);
     }
 }
 
@@ -10559,6 +10601,7 @@ TEST(json_import, geographic_crs_with_datum_ensemble) {
 
 TEST(json_import, datum_ensemble_without_ellipsoid) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DatumEnsemble\",\n"
                 "  \"name\": \"ensemble\",\n"
                 "  \"members\": [\n"
@@ -10576,13 +10619,16 @@ TEST(json_import, datum_ensemble_without_ellipsoid) {
     auto obj = createFromUserInput(json, nullptr);
     auto ensemble = nn_dynamic_pointer_cast<DatumEnsemble>(obj);
     ASSERT_TRUE(ensemble != nullptr);
-    EXPECT_EQ(ensemble->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(
+        ensemble->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+        json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, vertical_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"VerticalCRS\",\n"
                 "  \"name\": \"EGM2008 height\",\n"
                 "  \"datum\": {\n"
@@ -10605,10 +10651,12 @@ TEST(json_import, vertical_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<VerticalCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 
     auto datum = crs->datum();
-    auto datum_json = datum->exportToJSON((JSONFormatter::create().get()));
+    auto datum_json =
+        datum->exportToJSON(&(JSONFormatter::create()->setSchema("foo")));
     auto datum_obj = createFromUserInput(datum_json, nullptr);
     auto datum_got = nn_dynamic_pointer_cast<VerticalReferenceFrame>(datum_obj);
     ASSERT_TRUE(datum_got != nullptr);
@@ -10618,6 +10666,7 @@ TEST(json_import, vertical_crs) {
 
 TEST(json_import, vertical_crs_with_datum_ensemble) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"VerticalCRS\",\n"
                 "  \"name\": \"foo\",\n"
                 "  \"datum_ensemble\": {\n"
@@ -10649,13 +10698,15 @@ TEST(json_import, vertical_crs_with_datum_ensemble) {
     auto obj = createFromUserInput(json, nullptr);
     auto vcrs = nn_dynamic_pointer_cast<VerticalCRS>(obj);
     ASSERT_TRUE(vcrs != nullptr);
-    EXPECT_EQ(vcrs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(vcrs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, parametric_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"ParametricCRS\",\n"
                 "  \"name\": \"WMO standard atmosphere layer 0\",\n"
                 "  \"datum\": {\n"
@@ -10682,10 +10733,12 @@ TEST(json_import, parametric_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<ParametricCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 
     auto datum = crs->datum();
-    auto datum_json = datum->exportToJSON((JSONFormatter::create().get()));
+    auto datum_json =
+        datum->exportToJSON(&(JSONFormatter::create()->setSchema("foo")));
     auto datum_obj = createFromUserInput(datum_json, nullptr);
     auto datum_got = nn_dynamic_pointer_cast<ParametricDatum>(datum_obj);
     ASSERT_TRUE(datum_got != nullptr);
@@ -10695,6 +10748,7 @@ TEST(json_import, parametric_crs) {
 
 TEST(json_import, engineering_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"EngineeringCRS\",\n"
                 "  \"name\": \"Engineering CRS\",\n"
                 "  \"datum\": {\n"
@@ -10722,10 +10776,12 @@ TEST(json_import, engineering_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<EngineeringCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 
     auto datum = crs->datum();
-    auto datum_json = datum->exportToJSON((JSONFormatter::create().get()));
+    auto datum_json =
+        datum->exportToJSON(&(JSONFormatter::create()->setSchema("foo")));
     auto datum_obj = createFromUserInput(datum_json, nullptr);
     auto datum_got = nn_dynamic_pointer_cast<EngineeringDatum>(datum_obj);
     ASSERT_TRUE(datum_got != nullptr);
@@ -10735,6 +10791,7 @@ TEST(json_import, engineering_crs) {
 
 TEST(json_import, temporal_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"TemporalCRS\",\n"
                 "  \"name\": \"Temporal CRS\",\n"
                 "  \"datum\": {\n"
@@ -10757,10 +10814,12 @@ TEST(json_import, temporal_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<TemporalCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 
     auto datum = crs->datum();
-    auto datum_json = datum->exportToJSON((JSONFormatter::create().get()));
+    auto datum_json =
+        datum->exportToJSON(&(JSONFormatter::create()->setSchema("foo")));
     auto datum_obj = createFromUserInput(datum_json, nullptr);
     auto datum_got = nn_dynamic_pointer_cast<TemporalDatum>(datum_obj);
     ASSERT_TRUE(datum_got != nullptr);
@@ -10770,6 +10829,7 @@ TEST(json_import, temporal_crs) {
 
 TEST(json_import, derived_geodetic_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedGeodeticCRS\",\n"
                 "  \"name\": \"Derived geodetic CRS\",\n"
                 "  \"base_crs\": {\n"
@@ -10842,13 +10902,15 @@ TEST(json_import, derived_geodetic_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedGeodeticCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, derived_geographic_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedGeographicCRS\",\n"
                 "  \"name\": \"WMO Atlantic Pole\",\n"
                 "  \"base_crs\": {\n"
@@ -10925,13 +10987,15 @@ TEST(json_import, derived_geographic_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedGeographicCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, derived_projected_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedProjectedCRS\",\n"
                 "  \"name\": \"derived projectedCRS\",\n"
                 "  \"base_crs\": {\n"
@@ -11075,13 +11139,15 @@ TEST(json_import, derived_projected_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedProjectedCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, derived_vertical_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedVerticalCRS\",\n"
                 "  \"name\": \"Derived vertCRS\",\n"
                 "  \"base_crs\": {\n"
@@ -11131,13 +11197,15 @@ TEST(json_import, derived_vertical_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedVerticalCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, derived_engineering_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedEngineeringCRS\",\n"
                 "  \"name\": \"Derived EngineeringCRS\",\n"
                 "  \"base_crs\": {\n"
@@ -11198,13 +11266,15 @@ TEST(json_import, derived_engineering_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedEngineeringCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, derived_parametric_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedParametricCRS\",\n"
                 "  \"name\": \"Derived ParametricCRS\",\n"
                 "  \"base_crs\": {\n"
@@ -11261,13 +11331,15 @@ TEST(json_import, derived_parametric_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedParametricCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, derived_temporal_crs) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"DerivedTemporalCRS\",\n"
                 "  \"name\": \"Derived TemporalCRS\",\n"
                 "  \"base_crs\": {\n"
@@ -11321,13 +11393,15 @@ TEST(json_import, derived_temporal_crs) {
     auto obj = createFromUserInput(json, nullptr);
     auto crs = nn_dynamic_pointer_cast<DerivedTemporalCRS>(obj);
     ASSERT_TRUE(crs != nullptr);
-    EXPECT_EQ(crs->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(crs->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
 
 // ---------------------------------------------------------------------------
 
 TEST(json_import, multiple_ids) {
     auto json = "{\n"
+                "  \"$schema\": \"foo\",\n"
                 "  \"type\": \"Ellipsoid\",\n"
                 "  \"name\": \"WGS 84\",\n"
                 "  \"semi_major_axis\": 6378137,\n"
@@ -11346,5 +11420,6 @@ TEST(json_import, multiple_ids) {
     auto obj = createFromUserInput(json, nullptr);
     auto ellps = nn_dynamic_pointer_cast<Ellipsoid>(obj);
     ASSERT_TRUE(ellps != nullptr);
-    EXPECT_EQ(ellps->exportToJSON((JSONFormatter::create().get())), json);
+    EXPECT_EQ(ellps->exportToJSON(&(JSONFormatter::create()->setSchema("foo"))),
+              json);
 }
diff --git a/travis/install.sh b/travis/install.sh
index 249e0f2c..b2e13c12 100755
--- a/travis/install.sh
+++ b/travis/install.sh
@@ -55,24 +55,24 @@ find /tmp/proj_autoconf_install_from_dist_all
 /tmp/proj_autoconf_install_from_dist_all/bin/projinfo EPSG:32631 -o PROJJSON -q > out.json
 cat out.json
 echo "Validating JSON"
-jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/crsjson.schema.json && echo "Valid !"
+jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/projjson.schema.json && echo "Valid !"
 
 /tmp/proj_autoconf_install_from_dist_all/bin/projinfo EPSG:4326+3855 -o PROJJSON -q > out.json
 cat out.json
 echo "Validating JSON"
-jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/crsjson.schema.json && echo "Valid !"
+jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/projjson.schema.json && echo "Valid !"
 
 /tmp/proj_autoconf_install_from_dist_all/bin/projinfo "+proj=longlat +ellps=GRS80 +nadgrids=@foo +type=crs" -o PROJJSON -q > out.json
 cat out.json
 echo "Validating JSON"
-jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/crsjson.schema.json && echo "Valid !"
+jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/projjson.schema.json && echo "Valid !"
 /tmp/proj_autoconf_install_from_dist_all/bin/projinfo @out.json -o PROJJSON -q > out2.json
 diff -u out.json out2.json
 
 /tmp/proj_autoconf_install_from_dist_all/bin/projinfo -s EPSG:3111 -t GDA2020 -o PROJJSON -o PROJJSON -q > out.json
 cat out.json
 echo "Validating JSON"
-jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/crsjson.schema.json && echo "Valid !"
+jsonschema -i out.json /tmp/proj_autoconf_install_from_dist_all/share/proj/projjson.schema.json && echo "Valid !"
 /tmp/proj_autoconf_install_from_dist_all/bin/projinfo @out.json -o PROJJSON -q > out2.json
 diff -u out.json out2.json