Fix inplace nodata modification

geoutils/raster/multiraster.py

@@ -180,10 +180,14 @@ def stack_rasters(
             res=reference_raster.res,
             crs=reference_raster.crs,
             dtype=reference_raster.data.dtype,
-            nodata=reference_raster.nodata,
+            nodata=nodata,
             resampling=resampling_method,
             silent=True,
         )
+        # If the georeferenced grid was the same, reproject() will have returned self with a warning (silenced here),
+        # and we want to copy the raster before modifying its nodata (or it will modify raster inputs of this function)
+        if reprojected_raster.georeferenced_grid_equal(raster):
+            reprojected_raster = reprojected_raster.copy()
         reprojected_raster.set_nodata(nodata)
 
         # Optionally calculate difference

tests/test_raster/test_multiraster.py

@@ -243,6 +243,10 @@ def test_stack_rasters(self, rasters) -> None:  # type: ignore
         stacked_img = gu.raster.stack_rasters([rasters.img1, rasters.img2], resampling_method="bilinear")
         assert not np.array_equal(np.unique(stacked_img.data.compressed()), np.array([1, 5]))
 
+        # Check input nodata is not modified inplace (issue 609)
+        new_nodata_ref = rasters.img1.nodata
+        assert nodata_ref == new_nodata_ref
+
         # Check nodata value output is consistent with reference input
         if nodata_ref is not None:
             assert stacked_img.nodata == nodata_ref