PROJJSON export: use more compact form

9 files changed, 109 insertions, 69 deletions

diff --git a/data/crsjson.schema.json b/data/crsjson.schema.json
index 5ceeaa1e..86f1e13e 100644
--- a/data/crsjson.schema.json
+++ b/data/crsjson.schema.json
@@ -111,8 +111,8 @@
           "properties": {
             "type": { "type": "string", "enum": ["Ellipsoid"] },
             "name": { "type": "string" },
-            "semi_major_axis": { "$ref": "#/definitions/value_and_unit" },
-            "semi_minor_axis": { "$ref": "#/definitions/value_and_unit" },
+            "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": { "$ref": "#/definitions/id" }
           },
           "required" : [ "name", "semi_major_axis", "semi_minor_axis" ],
@@ -122,7 +122,7 @@
           "properties": {
             "type": { "type": "string", "enum": ["Ellipsoid"] },
             "name": { "type": "string" },
-            "semi_major_axis": { "$ref": "#/definitions/value_and_unit" },
+            "semi_major_axis": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
             "inverse_flattening": { "type": "number" },
             "id": { "$ref": "#/definitions/id" }
           },
@@ -133,7 +133,7 @@
           "properties": {
             "type": { "type": "string", "enum": ["Ellipsoid"] },
             "name": { "type": "string" },
-            "radius": { "$ref": "#/definitions/value_and_unit" },
+            "radius": { "$ref": "#/definitions/value_in_metre_or_value_and_unit" },
             "id": { "$ref": "#/definitions/id" }
           },
           "required" : [ "name", "radius" ],
@@ -255,17 +255,25 @@
     },
 
     "unit": {
-      "type": "object",
-      "properties": {
-        "type": { "type": "string",
-                  "enum": ["LinearUnit", "AngularUnit", "ScaleUnit",
-                           "TimeUnit", "ParametricUnit", "Unit"] },
-        "name": { "type": "string" },
-        "conversion_factor": { "type": "number" },
-        "id": { "$ref": "#/definitions/id" }
-       },
-       "required" : [ "type", "name" ],
-       "additionalProperties": false
+      "oneOf": [
+      {
+        "type": "string",
+        "enum": ["metre", "degree", "unity"]
+      },
+      {
+        "type": "object",
+        "properties": {
+          "type": { "type": "string",
+                    "enum": ["LinearUnit", "AngularUnit", "ScaleUnit",
+                             "TimeUnit", "ParametricUnit", "Unit"] },
+          "name": { "type": "string" },
+          "conversion_factor": { "type": "number" },
+          "id": { "$ref": "#/definitions/id" }
+         },
+         "required" : [ "type", "name" ],
+         "additionalProperties": false
+      }
+      ]
     },
 
     "usages": {
@@ -288,6 +296,13 @@
       },
       "required" : [ "value", "unit" ],
       "additionalProperties": false
+    },
+
+    "value_in_metre_or_value_and_unit": {
+      "oneOf": [
+        { "type": "number" },
+        { "$ref": "#/definitions/value_and_unit" }
+      ]
     }
 
   }
diff --git a/include/proj/io.hpp b/include/proj/io.hpp
index cfb4b3f7..043b4c4b 100644
--- a/include/proj/io.hpp
+++ b/include/proj/io.hpp
@@ -503,6 +503,8 @@ class PROJ_GCC_DLL JSONFormatter {
 
     PROJ_INTERNAL void setAllowIDInImmediateChild();
 
+    PROJ_INTERNAL void setOmitTypeInImmediateChild();
+
     // cppcheck-suppress functionStatic
     PROJ_INTERNAL bool outputId() const;
 
diff --git a/src/iso19111/coordinateoperation.cpp b/src/iso19111/coordinateoperation.cpp
index a2a31edd..f4e90fe8 100644
--- a/src/iso19111/coordinateoperation.cpp
+++ b/src/iso19111/coordinateoperation.cpp
@@ -1200,7 +1200,14 @@ void OperationParameterValue::_exportToJSON(
         writer.AddObjKey("value");
         writer.Add(l_value->value().value(), 15);
         writer.AddObjKey("unit");
-        l_value->value().unit()._exportToJSON(formatter);
+        const auto &l_unit(l_value->value().unit());
+        if (l_unit == common::UnitOfMeasure::METRE ||
+            l_unit == common::UnitOfMeasure::DEGREE ||
+            l_unit == common::UnitOfMeasure::SCALE_UNITY) {
+            writer.Add(l_unit.name());
+        } else {
+            l_unit._exportToJSON(formatter);
+        }
     } else if (l_value->type() == ParameterValue::Type::FILENAME) {
         writer.AddObjKey("value");
         writer.Add(l_value->valueFile());
@@ -5473,6 +5480,7 @@ void Conversion::_exportToJSON(
     }
 
     writer.AddObjKey("method");
+    formatter->setOmitTypeInImmediateChild();
     formatter->setAllowIDInImmediateChild();
     method()->_exportToJSON(formatter);
 
@@ -5481,6 +5489,7 @@ void Conversion::_exportToJSON(
         auto parametersContext(writer.MakeArrayContext(false));
         for (const auto &genOpParamvalue : parameterValues()) {
             formatter->setAllowIDInImmediateChild();
+            formatter->setOmitTypeInImmediateChild();
             genOpParamvalue->_exportToJSON(formatter);
         }
     }
diff --git a/src/iso19111/coordinatesystem.cpp b/src/iso19111/coordinatesystem.cpp
index f96a962f..ef53dd57 100644
--- a/src/iso19111/coordinatesystem.cpp
+++ b/src/iso19111/coordinatesystem.cpp
@@ -410,7 +410,13 @@ void CoordinateSystemAxis::_exportToJSON(
     writer.Add(direction().toString());
 
     writer.AddObjKey("unit");
-    unit()._exportToJSON(formatter);
+    const auto &l_unit(unit());
+    if (l_unit == common::UnitOfMeasure::METRE ||
+        l_unit == common::UnitOfMeasure::DEGREE) {
+        writer.Add(l_unit.name());
+    } else {
+        l_unit._exportToJSON(formatter);
+    }
 
     if (formatter->outputId()) {
         formatID(formatter);
@@ -577,6 +583,7 @@ void CoordinateSystem::_exportToJSON(
     auto axisContext(writer.MakeArrayContext(false));
     const auto &l_axisList = axisList();
     for (auto &axis : l_axisList) {
+        formatter->setOmitTypeInImmediateChild();
         axis->_exportToJSON(formatter);
     }
 
diff --git a/src/iso19111/crs.cpp b/src/iso19111/crs.cpp
index 2ca2786d..670d0c1a 100644
--- a/src/iso19111/crs.cpp
+++ b/src/iso19111/crs.cpp
@@ -1366,6 +1366,7 @@ void GeodeticCRS::_exportToJSON(
     }
 
     writer.AddObjKey("coordinate_system");
+    formatter->setOmitTypeInImmediateChild();
     coordinateSystem()->_exportToJSON(formatter);
 
     ObjectUsage::baseExportToJSON(formatter);
@@ -2116,6 +2117,7 @@ void GeographicCRS::_exportToJSON(
     }
 
     writer.AddObjKey("coordinate_system");
+    formatter->setOmitTypeInImmediateChild();
     coordinateSystem()->_exportToJSON(formatter);
 
     ObjectUsage::baseExportToJSON(formatter);
@@ -2940,12 +2942,15 @@ void ProjectedCRS::_exportToJSON(
 
     writer.AddObjKey("base_crs");
     formatter->setAllowIDInImmediateChild();
+    formatter->setOmitTypeInImmediateChild();
     baseCRS()->_exportToJSON(formatter);
 
     writer.AddObjKey("conversion");
+    formatter->setOmitTypeInImmediateChild();
     derivingConversionRef()->_exportToJSON(formatter);
 
     writer.AddObjKey("coordinate_system");
+    formatter->setOmitTypeInImmediateChild();
     coordinateSystem()->_exportToJSON(formatter);
 
     ObjectUsage::baseExportToJSON(formatter);
@@ -4316,6 +4321,7 @@ void DerivedGeodeticCRS::_exportToJSON(
     derivingConversionRef()->_exportToJSON(formatter);
 
     writer.AddObjKey("coordinate_system");
+    formatter->setOmitTypeInImmediateChild();
     coordinateSystem()->_exportToJSON(formatter);
 
     ObjectUsage::baseExportToJSON(formatter);
@@ -4485,6 +4491,7 @@ void DerivedGeographicCRS::_exportToJSON(
     derivingConversionRef()->_exportToJSON(formatter);
 
     writer.AddObjKey("coordinate_system");
+    formatter->setOmitTypeInImmediateChild();
     coordinateSystem()->_exportToJSON(formatter);
 
     ObjectUsage::baseExportToJSON(formatter);
diff --git a/src/iso19111/datum.cpp b/src/iso19111/datum.cpp
index 89ecc755..2944da1e 100644
--- a/src/iso19111/datum.cpp
+++ b/src/iso19111/datum.cpp
@@ -376,12 +376,13 @@ void PrimeMeridian::_exportToJSON(
 
     const auto &l_long = longitude();
     writer.AddObjKey("longitude");
-    {
+    const auto &unit = l_long.unit();
+    if (unit == common::UnitOfMeasure::DEGREE) {
+        writer.Add(l_long.value(), 15);
+    } else {
         auto longitudeContext(formatter->MakeObjectContext(nullptr, false));
         writer.AddObjKey("value");
         writer.Add(l_long.value(), 15);
-
-        const auto &unit = l_long.unit();
         writer.AddObjKey("unit");
         unit._exportToJSON(formatter);
     }
@@ -834,7 +835,9 @@ void Ellipsoid::_exportToJSON(
     const auto &semiMajor = semiMajorAxis();
     const auto &semiMajorUnit = semiMajor.unit();
     writer.AddObjKey(isSphere() ? "radius" : "semi_major_axis");
-    {
+    if (semiMajorUnit == common::UnitOfMeasure::METRE) {
+        writer.Add(semiMajor.value(), 15);
+    } else {
         auto objContext(formatter->MakeObjectContext(nullptr, false));
         writer.AddObjKey("value");
         writer.Add(semiMajor.value(), 15);
@@ -850,13 +853,17 @@ void Ellipsoid::_exportToJSON(
             writer.Add(l_inverseFlattening->getSIValue(), 15);
         } else {
             writer.AddObjKey("semi_minor_axis");
-            {
+            const auto &l_semiMinorAxis(semiMinorAxis());
+            const auto &semiMinorAxisUnit(l_semiMinorAxis->unit());
+            if (semiMinorAxisUnit == common::UnitOfMeasure::METRE) {
+                writer.Add(l_semiMinorAxis->value(), 15);
+            } else {
                 auto objContext(formatter->MakeObjectContext(nullptr, false));
                 writer.AddObjKey("value");
-                writer.Add(semiMinorAxis()->value(), 15);
+                writer.Add(l_semiMinorAxis->value(), 15);
 
                 writer.AddObjKey("unit");
-                semiMinorAxis()->unit()._exportToJSON(formatter);
+                semiMinorAxisUnit._exportToJSON(formatter);
             }
         }
     }
@@ -1272,10 +1279,15 @@ void GeodeticReferenceFrame::_exportToJSON(
     Datum::getPrivate()->exportAnchorDefinition(formatter);
 
     writer.AddObjKey("ellipsoid");
+    formatter->setOmitTypeInImmediateChild();
     ellipsoid()->_exportToJSON(formatter);
 
-    writer.AddObjKey("prime_meridian");
-    primeMeridian()->_exportToJSON(formatter);
+    const auto &l_primeMeridian(primeMeridian());
+    if (l_primeMeridian->nameStr() != "Greenwich") {
+        writer.AddObjKey("prime_meridian");
+        formatter->setOmitTypeInImmediateChild();
+        primeMeridian()->_exportToJSON(formatter);
+    }
 
     ObjectUsage::baseExportToJSON(formatter);
 }
diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index 35798d9d..bb15c80a 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -8027,6 +8027,7 @@ struct JSONFormatter::Private {
     std::vector<bool> stackHasId_{false};
     std::vector<bool> outputIdStack_{true};
     bool allowIDInImmediateChild_ = false;
+    bool omitTypeInImmediateChild_ = false;
 
     std::string result_{};
 
@@ -8102,14 +8103,21 @@ void JSONFormatter::setAllowIDInImmediateChild() {
 
 // ---------------------------------------------------------------------------
 
+void JSONFormatter::setOmitTypeInImmediateChild() {
+    d->omitTypeInImmediateChild_ = true;
+}
+
+// ---------------------------------------------------------------------------
+
 JSONFormatter::ObjectContext::ObjectContext(JSONFormatter &formatter,
                                             const char *objectType, bool hasId)
     : m_formatter(formatter) {
     m_formatter.d->writer_.StartObj();
-    if (objectType) {
+    if (objectType && !m_formatter.d->omitTypeInImmediateChild_) {
         m_formatter.d->writer_.AddObjKey("type");
         m_formatter.d->writer_.Add(objectType);
     }
+    m_formatter.d->omitTypeInImmediateChild_ = false;
     // All intermediate nodes shouldn't have ID if a parent has an ID
     // unless explicitly enabled.
     if (m_formatter.d->allowIDInImmediateChild_) {
diff --git a/test/cli/testprojinfo_out.dist b/test/cli/testprojinfo_out.dist
index 530a0426..73751b99 100644
--- a/test/cli/testprojinfo_out.dist
+++ b/test/cli/testprojinfo_out.dist
@@ -143,56 +143,25 @@ PROJJSON:
     "type": "GeodeticReferenceFrame",
     "name": "World Geodetic System 1984",
     "ellipsoid": {
-      "type": "Ellipsoid",
       "name": "WGS 84",
-      "semi_major_axis": {
-        "value": 6378137,
-        "unit": {
-          "type": "LinearUnit",
-          "name": "metre",
-          "conversion_factor": 1
-        }
-      },
+      "semi_major_axis": 6378137,
       "inverse_flattening": 298.257223563
-    },
-    "prime_meridian": {
-      "type": "PrimeMeridian",
-      "name": "Greenwich",
-      "longitude": {
-        "value": 0,
-        "unit": {
-          "type": "AngularUnit",
-          "name": "degree",
-          "conversion_factor": 0.0174532925199433
-        }
-      }
     }
   },
   "coordinate_system": {
-    "type": "CoordinateSystem",
     "subtype": "ellipsoidal",
     "axis": [
       {
-        "type": "Axis",
         "name": "Geodetic latitude",
         "abbreviation": "Lat",
         "direction": "north",
-        "unit": {
-          "type": "AngularUnit",
-          "name": "degree",
-          "conversion_factor": 0.0174532925199433
-        }
+        "unit": "degree"
       },
       {
-        "type": "Axis",
         "name": "Geodetic longitude",
         "abbreviation": "Lon",
         "direction": "east",
-        "unit": {
-          "type": "AngularUnit",
-          "name": "degree",
-          "conversion_factor": 0.0174532925199433
-        }
+        "unit": "degree"
       }
     ]
   },
diff --git a/test/unit/test_datum.cpp b/test/unit/test_datum.cpp
index cf2e2f3a..d8fab1f0 100644
--- a/test/unit/test_datum.cpp
+++ b/test/unit/test_datum.cpp
@@ -212,19 +212,30 @@ TEST(datum, prime_meridian_to_JSON) {
         "{\n"
         "  \"type\": \"PrimeMeridian\",\n"
         "  \"name\": \"Greenwich\",\n"
-        "  \"longitude\": {\n"
-        "    \"value\": 0,\n"
-        "    \"unit\": {\n"
-        "      \"type\": \"AngularUnit\",\n"
-        "      \"name\": \"degree\",\n"
-        "      \"conversion_factor\": 0.0174532925199433\n"
-        "    }\n"
-        "  },\n"
+        "  \"longitude\": 0,\n"
         "  \"id\": {\n"
         "    \"authority\": \"EPSG\",\n"
         "    \"code\": 8901\n"
         "  }\n"
         "}");
+
+    EXPECT_EQ(PrimeMeridian::PARIS->exportToJSON(JSONFormatter::create().get()),
+              "{\n"
+              "  \"type\": \"PrimeMeridian\",\n"
+              "  \"name\": \"Paris\",\n"
+              "  \"longitude\": {\n"
+              "    \"value\": 2.5969213,\n"
+              "    \"unit\": {\n"
+              "      \"type\": \"AngularUnit\",\n"
+              "      \"name\": \"grad\",\n"
+              "      \"conversion_factor\": 0.015707963267949\n"
+              "    }\n"
+              "  },\n"
+              "  \"id\": {\n"
+              "    \"authority\": \"EPSG\",\n"
+              "    \"code\": 8903\n"
+              "  }\n"
+              "}");
 }
 
 // ---------------------------------------------------------------------------