Early resampling: fix requests typical of pixel identification

qgis · Jun 19, 2020 · d2497c8 · d2497c8
1 parent 47da98c
commit d2497c8
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Showing 2 changed files with 22 additions and 4 deletions.
diff --git a/src/core/providers/gdal/qgsgdalprovider.cpp b/src/core/providers/gdal/qgsgdalprovider.cpp
@@ -958,10 +958,10 @@ bool QgsGdalProvider::readBlock( int bandNo, QgsRectangle  const &reqExtent, int
       sExtraArg.dfXSize = tgtWidth * reqXRes / srcXRes;
       sExtraArg.dfYSize = tgtHeight * reqYRes / -srcYRes;
       return GDALRasterIOEx( gdalBand, GF_Read,
-                             std::floor( sExtraArg.dfXOff ),
-                             std::floor( sExtraArg.dfYOff ),
-                             std::floor( sExtraArg.dfXSize ),
-                             std::floor( sExtraArg.dfYSize ),
+                             static_cast<int>( std::floor( sExtraArg.dfXOff ) ),
+                             static_cast<int>( std::floor( sExtraArg.dfYOff ) ),
+                             std::max( 1, static_cast<int>( std::floor( sExtraArg.dfXSize ) ) ),
+                             std::max( 1, static_cast<int>( std::floor( sExtraArg.dfYSize ) ) ),
                              static_cast<char *>( data ) +
                              ( tgtTop * bufferWidthPix + tgtLeft ) * dataSize,
                              tgtWidth,

diff --git a/tests/src/python/test_qgsrasterresampler.py b/tests/src/python/test_qgsrasterresampler.py
@@ -564,6 +564,24 @@ def testGDALResampling_nominal_resolution_slightly_overlapping_bottom_edge(self)
             # The values in the bottom line are not subject to resampling currently
             self.checkRawBlockContents(block, [[65, 100], [70, 190]])
 
+    def testGDALResampling_less_than_one_pixel(self):
+
+        xmin = 100
+        ymax = 1000
+        xres = 5
+        yres = 5
+
+        # Extent is less than one pixel. Simulates pixel identification
+        extent = QgsRectangle(xmin + 2.25 * xres,
+                              ymax - 4.25 * yres,
+                              xmin + 2.5 * xres,
+                              ymax - 4.5 * yres)
+
+        with self.setupGDALResampling() as provider:
+            provider.setZoomedInResamplingMethod(QgsRasterDataProvider.ResamplingMethod.Bilinear)
+            block = provider.block(1, extent, 1, 1)
+            self.checkRawBlockContents(block, [[68]])
+
 
 if __name__ == '__main__':
     unittest.main()