Always export GeoJSON features in WGS84 (match specifications)

python/core/qgsjsonutils.sip

@@ -1,6 +1,9 @@
 /** \ingroup core
  * \class QgsJSONExporter
  * \brief Handles exporting QgsFeature features to GeoJSON features.
+ *
+ * Note that geometries will be automatically reprojected to WGS84 to match GeoJSON spec
+ * if either the source vector layer or source CRS is set.
  * \note Added in version 2.16
  */
 
@@ -63,7 +66,8 @@ class QgsJSONExporter
      */
     bool includeRelated() const;
 
-    /** Sets the associated vector layer (required for related attribute export).
+    /** Sets the associated vector layer (required for related attribute export). This will automatically
+     * update the sourceCrs() to match.
      * @param vectorLayer vector layer
      * @see vectorLayer()
      */
@@ -74,6 +78,20 @@ class QgsJSONExporter
      */
     QgsVectorLayer* vectorLayer() const;
 
+    /** Sets the source CRS for feature geometries. The source CRS must be set if geometries are to be
+     * correctly automatically reprojected to WGS 84, to match GeoJSON specifications.
+     * @param crs source CRS for input feature geometries
+     * @note the source CRS will be overwritten when a vector layer is specified via setVectorLayer()
+     * @see sourceCrs()
+     */
+    void setSourceCrs( const QgsCoordinateReferenceSystem& crs );
+
+    /** Returns the source CRS for feature geometries. The source CRS must be set if geometries are to be
+     * correctly automatically reprojected to WGS 84, to match GeoJSON specifications.
+     * @see setSourceCrs()
+     */
+    const QgsCoordinateReferenceSystem& sourceCrs() const;
+
     /** Sets the list of attributes to include in the JSON exports.
      * @param attributes list of attribute indexes, or an empty list to include all
      * attributes
@@ -128,6 +146,10 @@ class QgsJSONExporter
      */
     QString exportFeatures( const QgsFeatureList& features ) const;
 
+  private:
+
+    QgsJSONExporter( const QgsJSONExporter& );
+
 };
 
 

src/core/qgsjsonutils.cpp

@@ -29,19 +29,40 @@ QgsJSONExporter::QgsJSONExporter( const QgsVectorLayer* vectorLayer, int precisi
     , mIncludeRelatedAttributes( false )
     , mLayerId( vectorLayer ? vectorLayer->id() : QString() )
 {
-
+  if ( vectorLayer )
+  {
+    mCrs = vectorLayer->crs();
+    mTransform.setSourceCrs( mCrs );
+  }
+  mTransform.setDestCRS( QgsCoordinateReferenceSystem( 4326, QgsCoordinateReferenceSystem::EpsgCrsId ) );
 }
 
 void QgsJSONExporter::setVectorLayer( const QgsVectorLayer* vectorLayer )
 {
   mLayerId = vectorLayer ? vectorLayer->id() : QString();
+  if ( vectorLayer )
+  {
+    mCrs = vectorLayer->crs();
+    mTransform.setSourceCrs( mCrs );
+  }
 }
 
 QgsVectorLayer *QgsJSONExporter::vectorLayer() const
 {
   return qobject_cast< QgsVectorLayer* >( QgsMapLayerRegistry::instance()->mapLayer( mLayerId ) );
 }
 
+void QgsJSONExporter::setSourceCrs( const QgsCoordinateReferenceSystem& crs )
+{
+  mCrs = crs;
+  mTransform.setSourceCrs( mCrs );
+}
+
+const QgsCoordinateReferenceSystem& QgsJSONExporter::sourceCrs() const
+{
+  return mCrs;
+}
+
 QString QgsJSONExporter::exportFeature( const QgsFeature& feature, const QVariantMap& extraProperties,
                                         const QVariant& id ) const
 {
@@ -53,18 +74,30 @@ QString QgsJSONExporter::exportFeature( const QgsFeature& feature, const QVarian
   const QgsGeometry* geom = feature.constGeometry();
   if ( geom && !geom->isEmpty() && mIncludeGeometry )
   {
-    QgsRectangle box = geom->boundingBox();
+    const QgsGeometry* exportGeom = geom;
+    if ( mCrs.isValid() )
+    {
+      QgsGeometry* clone = new QgsGeometry( *geom );
+      if ( clone->transform( mTransform ) == 0 )
+        exportGeom = clone;
+      else
+        delete clone;
+    }
+    QgsRectangle box = exportGeom->boundingBox();
 
-    if ( QgsWKBTypes::flatType( geom->geometry()->wkbType() ) != QgsWKBTypes::Point )
+    if ( QgsWKBTypes::flatType( exportGeom->geometry()->wkbType() ) != QgsWKBTypes::Point )
     {
       s += QString( "   \"bbox\":[%1, %2, %3, %4],\n" ).arg( qgsDoubleToString( box.xMinimum(), mPrecision ),
            qgsDoubleToString( box.yMinimum(), mPrecision ),
            qgsDoubleToString( box.xMaximum(), mPrecision ),
            qgsDoubleToString( box.yMaximum(), mPrecision ) );
     }
     s += "   \"geometry\":\n   ";
-    s += geom->exportToGeoJSON( mPrecision );
+    s += exportGeom->exportToGeoJSON( mPrecision );
     s += ",\n";
+
+    if ( exportGeom != geom )
+      delete exportGeom;
   }
   else
   {

src/core/qgsjsonutils.h

@@ -17,13 +17,18 @@
 #define QGSJSONUTILS_H
 
 #include "qgsfeature.h"
+#include "qgscoordinatereferencesystem.h"
+#include "qgscoordinatetransform.h"
 
 class QTextCodec;
 class QgsVectorLayer;
 
 /** \ingroup core
  * \class QgsJSONExporter
  * \brief Handles exporting QgsFeature features to GeoJSON features.
+ *
+ * Note that geometries will be automatically reprojected to WGS84 to match GeoJSON spec
+ * if either the source vector layer or source CRS is set.
  * \note Added in version 2.16
  */
 
@@ -83,7 +88,8 @@ class CORE_EXPORT QgsJSONExporter
      */
     bool includeRelated() const { return mIncludeRelatedAttributes; }
 
-    /** Sets the associated vector layer (required for related attribute export).
+    /** Sets the associated vector layer (required for related attribute export). This will automatically
+     * update the sourceCrs() to match.
      * @param vectorLayer vector layer
      * @see vectorLayer()
      */
@@ -94,6 +100,20 @@ class CORE_EXPORT QgsJSONExporter
      */
     QgsVectorLayer* vectorLayer() const;
 
+    /** Sets the source CRS for feature geometries. The source CRS must be set if geometries are to be
+     * correctly automatically reprojected to WGS 84, to match GeoJSON specifications.
+     * @param crs source CRS for input feature geometries
+     * @note the source CRS will be overwritten when a vector layer is specified via setVectorLayer()
+     * @see sourceCrs()
+     */
+    void setSourceCrs( const QgsCoordinateReferenceSystem& crs );
+
+    /** Returns the source CRS for feature geometries. The source CRS must be set if geometries are to be
+     * correctly automatically reprojected to WGS 84, to match GeoJSON specifications.
+     * @see setSourceCrs()
+     */
+    const QgsCoordinateReferenceSystem& sourceCrs() const;
+
     /** Sets the list of attributes to include in the JSON exports.
      * @param attributes list of attribute indexes, or an empty list to include all
      * attributes
@@ -148,7 +168,6 @@ class CORE_EXPORT QgsJSONExporter
      */
     QString exportFeatures( const QgsFeatureList& features ) const;
 
-
   private:
 
     //! Maximum number of decimal places for geometry coordinates
@@ -173,6 +192,10 @@ class CORE_EXPORT QgsJSONExporter
     //! Layer ID of associated vector layer. Required for related attribute export.
     QString mLayerId;
 
+    QgsCoordinateReferenceSystem mCrs;
+
+    QgsCoordinateTransform mTransform;
+
 };
 
 /** \ingroup core

tests/src/python/test_qgsjsonutils.py

@@ -15,7 +15,22 @@
 import qgis  # NOQA
 
 from qgis.testing import unittest, start_app
-from qgis.core import QgsJSONUtils, QgsJSONExporter, QgsProject, QgsMapLayerRegistry, QgsFeature, QgsField, QgsFields, QgsWKBTypes, QgsGeometry, QgsPointV2, QgsLineStringV2, NULL, QgsVectorLayer, QgsRelation
+from qgis.core import (QgsJSONUtils,
+                       QgsJSONExporter,
+                       QgsCoordinateReferenceSystem,
+                       QgsProject,
+                       QgsMapLayerRegistry,
+                       QgsFeature,
+                       QgsField,
+                       QgsFields,
+                       QgsWKBTypes,
+                       QgsGeometry,
+                       QgsPointV2,
+                       QgsLineStringV2,
+                       NULL,
+                       QgsVectorLayer,
+                       QgsRelation
+                       )
 from qgis.PyQt.QtCore import QVariant, QTextCodec
 
 start_app()
@@ -364,6 +379,45 @@ def testJSONExporter(self):
         self.assertEqual(exporter.exportFeature(feature, extraProperties={"extra": "val1", "extra2": {"nested_map": 5, "nested_map2": "val"}, "extra3": [1, 2, 3]}), expected)
         exporter.setIncludeGeometry(True)
 
+    def testExportFeatureCrs(self):
+        """ Test CRS transform when exporting features """
+
+        exporter = QgsJSONExporter()
+        self.assertFalse(exporter.sourceCrs().isValid())
+
+        #test layer
+        layer = QgsVectorLayer("Point?crs=epsg:3111&field=fldtxt:string",
+                               "parent", "memory")
+        exporter = QgsJSONExporter(layer)
+        self.assertTrue(exporter.sourceCrs().isValid())
+        self.assertEqual(exporter.sourceCrs().authid(), 'EPSG:3111')
+
+        exporter.setSourceCrs(QgsCoordinateReferenceSystem(3857, QgsCoordinateReferenceSystem.EpsgCrsId))
+        self.assertTrue(exporter.sourceCrs().isValid())
+        self.assertEqual(exporter.sourceCrs().authid(), 'EPSG:3857')
+
+        # vector layer CRS should override
+        exporter.setVectorLayer(layer)
+        self.assertEqual(exporter.sourceCrs().authid(), 'EPSG:3111')
+
+        # test that exported feature is reprojected
+        feature = QgsFeature(layer.fields(), 5)
+        feature.setGeometry(QgsGeometry(QgsPointV2(2502577, 2403869)))
+        feature.setAttributes(['test point'])
+
+        # low precision, only need rough coordinate to check and don't want to deal with rounding errors
+        exporter.setPrecision(1)
+        expected = """{
+   "type":"Feature",
+   "id":5,
+   "geometry":
+   {"type": "Point", "coordinates": [145, -37.9]},
+   "properties":{
+      "fldtxt":"test point"
+   }
+}"""
+        self.assertEqual(exporter.exportFeature(feature), expected)
+
     def testExportFeatureRelations(self):
         """ Test exporting a feature with relations """