Fixed #31766 -- Avoided uncessary computation in GDALRaster

Implemented a clone method using ds_copy to clone GDALRaster objects. Added conditional to simply clone GDALRaster if SRID matches with transform srs argument.

AUTHORS

@@ -110,6 +110,7 @@ answer newbie questions, and generally made Django that much better:
     Baptiste Mispelon <bmispelon@gmail.com>
     Barry Pederson <bp@barryp.org>
     Bartolome Sanchez Salado <i42sasab@uco.es>
+    Barton Ip <notbartonip@gmail.com>
     Bartosz Grabski <bartosz.grabski@gmail.com>
     Bashar Al-Abdulhadi
     Bastian Kleineidam <calvin@debian.org>

django/contrib/gis/gdal/raster/source.py

@@ -425,6 +425,21 @@ def warp(self, ds_input, resampling='NearestNeighbour', max_error=0.0):
 
         return target
 
+    def clone(self):
+        """Return a clone of this GDALRaster."""
+        return GDALRaster(
+            capi.copy_ds(
+                self.driver._ptr,
+                force_bytes(self.name),
+                self._ptr,
+                c_int(),
+                c_char_p(),
+                c_void_p(),
+                c_void_p(),
+            ),
+            write=self._write,
+        )
+
     def transform(self, srs, driver=None, name=None, resampling='NearestNeighbour',
                   max_error=0.0):
         """
@@ -443,6 +458,9 @@ def transform(self, srs, driver=None, name=None, resampling='NearestNeighbour',
                 'Transform only accepts SpatialReference, string, and integer '
                 'objects.'
             )
+
+        if target_srs.srid == self.srid:
+            return self.clone()
         # Create warped virtual dataset in the target reference system
         target = capi.auto_create_warped_vrt(
             self._ptr, self.srs.wkt.encode(), target_srs.wkt.encode(),

tests/gis_tests/gdal_tests/test_raster.py

@@ -2,6 +2,7 @@
 import shutil
 import struct
 import tempfile
+from unittest import mock
 
 from django.contrib.gis.gdal import GDAL_VERSION, GDALRaster, SpatialReference
 from django.contrib.gis.gdal.error import GDALException
@@ -470,6 +471,33 @@ def test_raster_warp_nodata_zone(self):
         # The result is an empty raster filled with the correct nodata value.
         self.assertEqual(result, [23] * 16)
 
+    def test_raster_clone(self):
+        # Create in memory raster.
+        source = GDALRaster({
+            'datatype': 1,
+            'driver': 'MEM',
+            'width': 4,
+            'height': 4,
+            'srid': 3086,
+            'origin': (500000, 400000),
+            'scale': (100, -100),
+            'skew': (0, 0),
+            'bands': [{
+                'data': range(16),
+                'nodata_value': 23,
+            }],
+        })
+        clone = source.clone()
+        self.assertEqual(clone.name, source.name)
+        self.assertEqual(clone._write, source._write)
+        self.assertEqual(clone.srs.srid, source.srs.srid)
+        self.assertEqual(clone.width, source.width)
+        self.assertEqual(clone.height, source.height)
+        self.assertEqual(clone.origin, source.origin)
+        self.assertEqual(clone.scale, source.scale)
+        self.assertEqual(clone.skew, source.skew)
+        self.assertIsNot(clone, source)
+
     def test_raster_transform(self):
         tests = [
             3086,
@@ -531,6 +559,31 @@ def test_raster_transform(self):
                     ],
                 )
 
+    def test_raster_transform_clone(self):
+        with mock.patch.object(GDALRaster, 'clone') as mocked_clone:
+            # Create in file based raster.
+            rstfile = tempfile.NamedTemporaryFile(suffix='.tif')
+            ndv = 99
+            source = GDALRaster({
+                'datatype': 1,
+                'driver': 'tif',
+                'name': rstfile.name,
+                'width': 5,
+                'height': 5,
+                'nr_of_bands': 1,
+                'srid': 4326,
+                'origin': (-5, 5),
+                'scale': (2, -2),
+                'skew': (0, 0),
+                'bands': [{
+                    'data': range(25),
+                    'nodata_value': ndv,
+                }],
+            })
+            # transform() returns a clone because it is the same SRID.
+            target = source.transform(4326)
+            self.assertEqual(mocked_clone.call_count, 1)
+
 
 class GDALBandTests(SimpleTestCase):
     rs_path = os.path.join(os.path.dirname(__file__), '../data/rasters/raster.tif')