[fix] Set transform argument to None by default

This is to be backwards-compatible with previous versions

Author: StefanBrand

README.rst

@@ -97,7 +97,7 @@ This field takes four optional arguments:
 - ``auto_bbox``: If ``True``, the GeoJSON object will include
   a `bounding box <https://datatracker.ietf.org/doc/html/rfc7946#section-5>`_,
   which is the smallest possible rectangle enclosing the geometry.
-- ``transform`` (defaults to ``4326``): If ``None`` (or the input geometry does not have
+- ``transform`` (defaults to ``None``): If ``None`` (or the input geometry does not have
   a SRID), the GeoJSON's coordinates will not be transformed. If any other `spatial
   reference <https://docs.djangoproject.com/en/5.0/ref/contrib/gis/geos/#django.contrib.gis.geos.GEOSGeometry.transform>`,
    the GeoJSON's coordinates will be transformed correspondingly.

rest_framework_gis/fields.py

@@ -22,7 +22,7 @@ def __init__(
         precision=None,
         remove_duplicates=False,
         auto_bbox=False,
-        transform=4326,
+        transform=None,
         **kwargs,
     ):
         """
@@ -41,11 +41,7 @@ def to_representation(self, value):
         # we expect value to be a GEOSGeometry instance
         if value.geojson:
             # NOTE: For repeated transformations a gdal.CoordTransform is recommended
-            if (
-                self.transform is not None
-                and value.srid is not None
-                and value.srid != 4326
-            ):
+            if self.transform is not None and value.srid is not None:
                 value.transform(self.transform)
 
             geojson = GeoJsonDict(value.geojson)

tests/django_restframework_gis_tests/serializers.py

@@ -58,7 +58,7 @@ class Meta:
 class OtherSridLocationGeoSerializer(gis_serializers.GeoFeatureModelSerializer):
     """Other SRID location geo serializer"""
 
-    geometry = GeometryField(auto_bbox=True)
+    geometry = GeometryField(auto_bbox=True, transform=4326)
 
     class Meta:
         model = OtherSridLocation

tests/django_restframework_gis_tests/test_fields.py

@@ -196,7 +196,7 @@ def test_transform_Point_no_srid(self):
     def test_transform_Point_to_4326(self):
         model = self.get_instance(Point31287)
         model.geometry.srid = 31287
-        Serializer = self.create_serializer()
+        Serializer = self.create_serializer(transform=4326)
         data = Serializer(model).data
 
         expected_coords = (16.372500007573713, 48.20833306345481)
@@ -222,7 +222,7 @@ def test_transform_Point_to_3857(self):
     def test_transform_Point_bbox_to_4326(self):
         model = self.get_instance(Point31287)
         model.geometry.srid = 31287
-        Serializer = self.create_serializer(auto_bbox=True)
+        Serializer = self.create_serializer(auto_bbox=True, transform=4326)
         data = Serializer(model).data
 
         expected_coords = (