RasterDataset: calculate res after changing crs (#2193)

* RasterDataset: recalculate res after crs changes

* Add unit tests

* Fix style

* One less line of code

tests/datasets/test_geo.py

@@ -1,5 +1,7 @@
 # Copyright (c) Microsoft Corporation. All rights reserved.
 # Licensed under the MIT License.
+
+import math
 import os
 import pickle
 import sys
@@ -277,6 +279,11 @@ def test_getitem_separate_files(self, sentinel: Sentinel2) -> None:
         assert isinstance(x['image'], torch.Tensor)
         assert len(sentinel.bands) == x['image'].shape[0]
 
+    def test_reprojection(self, naip: NAIP) -> None:
+        naip2 = NAIP(naip.paths, crs='EPSG:4326')
+        assert naip.crs != naip2.crs
+        assert not math.isclose(naip.res, naip2.res)
+
     @pytest.mark.parametrize('dtype', ['uint16', 'uint32'])
     def test_getitem_uint_dtype(self, dtype: str) -> None:
         root = os.path.join('tests', 'data', 'raster', dtype)

torchgeo/datasets/geo.py

@@ -461,11 +461,11 @@ def __init__(
 
                         if crs is None:
                             crs = src.crs
-                        if res is None:
-                            res = src.res[0]
 
                         with WarpedVRT(src, crs=crs) as vrt:
                             minx, miny, maxx, maxy = vrt.bounds
+                            if res is None:
+                                res = vrt.res[0]
                 except rasterio.errors.RasterioIOError:
                     # Skip files that rasterio is unable to read
                     continue