ENH: Implement fast coordinate transformations.

skimage/transform/tests/test_project.py

@@ -1,7 +1,7 @@
 import numpy as np
 from numpy.testing import assert_array_almost_equal
 
-from skimage.transform.project import _stackcopy
+from skimage.transform._warp import _stackcopy
 from skimage.transform import homography, fast_homography
 from skimage import data
 from skimage.color import rgb2gray

skimage/transform/tests/test_swirl.py

@@ -0,0 +1,18 @@
+import numpy as np
+from numpy.testing import assert_array_almost_equal
+
+from skimage import transform as tf, data, img_as_float
+
+
+def test_roundtrip():
+    image = img_as_float(data.checkerboard())
+    swirl_params = {'radius': 80, 'rotation': 0, 'order': 2, 'mode': 'reflect'}
+    unswirled = tf.swirl(
+        tf.swirl(image, strength=10, **swirl_params),
+        strength=-10, **swirl_params
+        )
+
+    assert np.mean(np.abs(image - unswirled)) < 0.01
+
+if __name__ == "__main__":
+    np.testing.run_module_suite()