createFromWkt(): be tolerant to missing scale_factor parameter (fixes #1700)

This is invalid WKT, but GDAL 2.4 used to accept it and make a reasonable
use of it...

Currently we default it to 0 which is non sensical. Better use 1 as GDAL 2.4
did, and emit a warning.

Other fix: proj_create_from_wkt() was documented to operate by default in
non-strict validation mode, but it was actually in strict mode. So do as
documented.

5 files changed, 128 insertions, 20 deletions

diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index f5f7ba55..337de313 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -498,7 +498,7 @@ template <class T> static PROJ_STRING_LIST to_string_list(T &&set) {
  * proj_string_list_destroy().
  * @param out_grammar_errors Pointer to a PROJ_STRING_LIST object, or NULL.
  * If provided, *out_grammar_errors will contain a list of errors regarding the
- * WKT grammaer. It must be freed with proj_string_list_destroy().
+ * WKT grammar. It must be freed with proj_string_list_destroy().
  * @return Object that must be unreferenced with proj_destroy(), or NULL in
  * case of error.
  */
@@ -522,6 +522,7 @@ PJ *proj_create_from_wkt(PJ_CONTEXT *ctx, const char *wkt,
         if (dbContext) {
             parser.attachDatabaseContext(NN_NO_CHECK(dbContext));
         }
+        parser.setStrict(false);
         for (auto iter = options; iter && iter[0]; ++iter) {
             const char *value;
             if ((value = getOptionValue(*iter, "STRICT="))) {
@@ -536,10 +537,19 @@ PJ *proj_create_from_wkt(PJ_CONTEXT *ctx, const char *wkt,
         auto obj = nn_dynamic_pointer_cast<IdentifiedObject>(
             parser.createFromWKT(wkt));
 
+        std::vector<std::string> warningsFromParsing;
         if (out_grammar_errors) {
-            auto warnings = parser.warningList();
-            if (!warnings.empty()) {
-                *out_grammar_errors = to_string_list(warnings);
+            auto rawWarnings = parser.warningList();
+            std::vector<std::string> grammarWarnings;
+            for (const auto &msg : rawWarnings) {
+                if (msg.find("Default it to") != std::string::npos) {
+                    warningsFromParsing.push_back(msg);
+                } else {
+                    grammarWarnings.push_back(msg);
+                }
+            }
+            if (!grammarWarnings.empty()) {
+                *out_grammar_errors = to_string_list(grammarWarnings);
             }
         }
 
@@ -548,6 +558,8 @@ PJ *proj_create_from_wkt(PJ_CONTEXT *ctx, const char *wkt,
             if (derivedCRS) {
                 auto warnings =
                     derivedCRS->derivingConversionRef()->validateParameters();
+                warnings.insert(warnings.end(), warningsFromParsing.begin(),
+                                warningsFromParsing.end());
                 if (!warnings.empty()) {
                     *out_warnings = to_string_list(warnings);
                 }
diff --git a/src/iso19111/coordinateoperation.cpp b/src/iso19111/coordinateoperation.cpp
index c7581642..5ac81aa1 100644
--- a/src/iso19111/coordinateoperation.cpp
+++ b/src/iso19111/coordinateoperation.cpp
@@ -6056,24 +6056,31 @@ void Conversion::_exportToPROJString(
                 if (!param->proj_name) {
                     continue;
                 }
-                auto value =
+                const auto value =
                     parameterValueMeasure(param->wkt2_name, param->epsg_code);
+                double valueConverted = 0;
+                if (value == nullMeasure) {
+                    // Deal with missing values. In an ideal world, this would
+                    // not happen
+                    if (param->epsg_code ==
+                        EPSG_CODE_PARAMETER_SCALE_FACTOR_AT_NATURAL_ORIGIN) {
+                        valueConverted = 1.0;
+                    }
+                } else if (param->unit_type ==
+                           common::UnitOfMeasure::Type::ANGULAR) {
+                    valueConverted =
+                        value.convertToUnit(common::UnitOfMeasure::DEGREE);
+                } else {
+                    valueConverted = value.getSIValue();
+                }
+
                 if (mapping->epsg_code ==
                         EPSG_CODE_METHOD_LAMBERT_CONIC_CONFORMAL_1SP &&
                     strcmp(param->proj_name, "lat_1") == 0) {
-                    formatter->addParam(
-                        param->proj_name,
-                        value.convertToUnit(common::UnitOfMeasure::DEGREE));
-                    formatter->addParam(
-                        "lat_0",
-                        value.convertToUnit(common::UnitOfMeasure::DEGREE));
-                } else if (param->unit_type ==
-                           common::UnitOfMeasure::Type::ANGULAR) {
-                    formatter->addParam(
-                        param->proj_name,
-                        value.convertToUnit(common::UnitOfMeasure::DEGREE));
+                    formatter->addParam(param->proj_name, valueConverted);
+                    formatter->addParam("lat_0", valueConverted);
                 } else {
-                    formatter->addParam(param->proj_name, value.getSIValue());
+                    formatter->addParam(param->proj_name, valueConverted);
                 }
             }
 
diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index fc66b6c9..50ad5a87 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -3476,6 +3476,14 @@ ConversionNNPtr WKTParser::Private::buildProjectionStandard(
     }
     propertiesMethod.set(IdentifiedObject::NAME_KEY, projectionName);
 
+    std::vector<bool> foundParameters;
+    if (mapping) {
+        size_t countParams = 0;
+        while (mapping->params[countParams] != nullptr) {
+            ++countParams;
+        }
+        foundParameters.resize(countParams);
+    }
     for (const auto &childNode : projCRSNode->GP()->children()) {
         if (ci_equal(childNode->GP()->value(), WKTConstants::PARAMETER)) {
             const auto &childNodeChildren = childNode->GP()->children();
@@ -3496,11 +3504,18 @@ ConversionNNPtr WKTParser::Private::buildProjectionStandard(
                     continue;
                 }
             }
-            const auto *paramMapping =
+            auto *paramMapping =
                 mapping ? getMappingFromWKT1(mapping, parameterName) : nullptr;
             if (mapping &&
                 mapping->epsg_code == EPSG_CODE_METHOD_MERCATOR_VARIANT_B &&
                 ci_equal(parameterName, "latitude_of_origin")) {
+                for (size_t idx = 0; mapping->params[idx] != nullptr; ++idx) {
+                    if (mapping->params[idx]->epsg_code ==
+                        EPSG_CODE_PARAMETER_LATITUDE_OF_NATURAL_ORIGIN) {
+                        foundParameters[idx] = true;
+                        break;
+                    }
+                }
                 parameterName = EPSG_NAME_PARAMETER_LATITUDE_OF_NATURAL_ORIGIN;
                 propertiesParameter.set(
                     Identifier::CODE_KEY,
@@ -3508,6 +3523,12 @@ ConversionNNPtr WKTParser::Private::buildProjectionStandard(
                 propertiesParameter.set(Identifier::CODESPACE_KEY,
                                         Identifier::EPSG);
             } else if (paramMapping) {
+                for (size_t idx = 0; mapping->params[idx] != nullptr; ++idx) {
+                    if (mapping->params[idx] == paramMapping) {
+                        foundParameters[idx] = true;
+                        break;
+                    }
+                }
                 parameterName = paramMapping->wkt2_name;
                 if (paramMapping->epsg_code != 0) {
                     propertiesParameter.set(Identifier::CODE_KEY,
@@ -3531,6 +3552,38 @@ ConversionNNPtr WKTParser::Private::buildProjectionStandard(
         }
     }
 
+    // Add back important parameters that should normally be present, but
+    // are sometimes missing. Currently we only deal with Scale factor at
+    // natural origin. This is to avoid a default value of 0 to slip in later.
+    // But such WKT should be considered invalid.
+    if (mapping) {
+        for (size_t idx = 0; mapping->params[idx] != nullptr; ++idx) {
+            if (!foundParameters[idx] &&
+                mapping->params[idx]->epsg_code ==
+                    EPSG_CODE_PARAMETER_SCALE_FACTOR_AT_NATURAL_ORIGIN) {
+
+                emitRecoverableWarning(
+                    "The WKT string lacks a value "
+                    "for " EPSG_NAME_PARAMETER_SCALE_FACTOR_AT_NATURAL_ORIGIN
+                    ". Default it to 1.");
+
+                PropertyMap propertiesParameter;
+                propertiesParameter.set(
+                    Identifier::CODE_KEY,
+                    EPSG_CODE_PARAMETER_SCALE_FACTOR_AT_NATURAL_ORIGIN);
+                propertiesParameter.set(Identifier::CODESPACE_KEY,
+                                        Identifier::EPSG);
+                propertiesParameter.set(
+                    IdentifiedObject::NAME_KEY,
+                    EPSG_NAME_PARAMETER_SCALE_FACTOR_AT_NATURAL_ORIGIN);
+                parameters.push_back(
+                    OperationParameter::create(propertiesParameter));
+                values.push_back(ParameterValue::create(
+                    Measure(1.0, UnitOfMeasure::SCALE_UNITY)));
+            }
+        }
+    }
+
     return Conversion::create(
                PropertyMap().set(IdentifiedObject::NAME_KEY, "unnamed"),
                propertiesMethod, parameters, values)
diff --git a/test/unit/test_c_api.cpp b/test/unit/test_c_api.cpp
index 8ac5a511..b8310ce5 100644
--- a/test/unit/test_c_api.cpp
+++ b/test/unit/test_c_api.cpp
@@ -231,7 +231,8 @@ TEST_F(CApi, proj_create_from_wkt) {
             "    PRIMEM[\"Greenwich\",0],\n"
             "    UNIT[\"degree\",0.0174532925199433]]",
             nullptr, nullptr, nullptr);
-        EXPECT_EQ(obj, nullptr);
+        ObjectKeeper keeper(obj);
+        EXPECT_NE(obj, nullptr);
     }
     {
         PROJ_STRING_LIST warningList = nullptr;
@@ -244,7 +245,8 @@ TEST_F(CApi, proj_create_from_wkt) {
             "    PRIMEM[\"Greenwich\",0],\n"
             "    UNIT[\"degree\",0.0174532925199433]]",
             nullptr, &warningList, &errorList);
-        EXPECT_EQ(obj, nullptr);
+        ObjectKeeper keeper(obj);
+        EXPECT_NE(obj, nullptr);
         EXPECT_EQ(warningList, nullptr);
         proj_string_list_destroy(warningList);
         EXPECT_NE(errorList, nullptr);
diff --git a/test/unit/test_io.cpp b/test/unit/test_io.cpp
index 074a59b9..8aff0908 100644
--- a/test/unit/test_io.cpp
+++ b/test/unit/test_io.cpp
@@ -1174,6 +1174,40 @@ TEST(wkt_parse, wkt1_Mercator_1SP_with_latitude_origin_0) {
 
 // ---------------------------------------------------------------------------
 
+TEST(wkt_parse, wkt1_Mercator_1SP_without_scale_factor) {
+    // See https://github.com/OSGeo/PROJ/issues/1700
+    auto wkt = "PROJCS[\"unnamed\",\n"
+               "    GEOGCS[\"WGS 84\",\n"
+               "        DATUM[\"unknown\",\n"
+               "            SPHEROID[\"WGS84\",6378137,298.257223563]],\n"
+               "        PRIMEM[\"Greenwich\",0],\n"
+               "        UNIT[\"degree\",0.0174532925199433]],\n"
+               "    PROJECTION[\"Mercator_1SP\"],\n"
+               "    PARAMETER[\"central_meridian\",0],\n"
+               "    PARAMETER[\"false_easting\",0],\n"
+               "    PARAMETER[\"false_northing\",0],\n"
+               "    UNIT[\"Meter\",1],\n"
+               "    AXIS[\"Easting\",EAST],\n"
+               "    AXIS[\"Northing\",NORTH]]";
+    WKTParser parser;
+    parser.setStrict(false).attachDatabaseContext(DatabaseContext::create());
+    auto obj = parser.createFromWKT(wkt);
+    EXPECT_TRUE(!parser.warningList().empty());
+
+    auto crs = nn_dynamic_pointer_cast<ProjectedCRS>(obj);
+    ASSERT_TRUE(crs != nullptr);
+    auto got_wkt = crs->exportToWKT(
+        WKTFormatter::create(WKTFormatter::Convention::WKT1_GDAL).get());
+    EXPECT_TRUE(got_wkt.find("PARAMETER[\"scale_factor\",1]") !=
+                std::string::npos)
+        << got_wkt;
+    EXPECT_EQ(crs->exportToPROJString(PROJStringFormatter::create().get()),
+              "+proj=merc +lon_0=0 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +units=m "
+              "+no_defs +type=crs");
+}
+
+// ---------------------------------------------------------------------------
+
 TEST(wkt_parse, wkt1_krovak_south_west) {
     auto wkt =
         "PROJCS[\"S-JTSK / Krovak\","