Add window_transform method.

Closes #215
rasterio · Feb 9, 2015 · c79e88f · c79e88f
1 parent 99e9689
commit c79e88f
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diff --git a/rasterio/_base.pyx b/rasterio/_base.pyx
@@ -379,6 +379,11 @@ cdef class DatasetReader(object):
         lr = self.index(right, bottom)
         return tuple(zip(ul, lr))
 
+    def window_transform(self, window):
+        """Returns the affine transform for a dataset window."""
+        (r, _), (c, _) = window
+        return self.affine * Affine.translation(c or 0, r or 0)
+
     @property
     def meta(self):
         m = {

diff --git a/tests/test_transform.py b/tests/test_transform.py
@@ -1,4 +1,3 @@
-
 import rasterio
 
 def test_window():
@@ -9,3 +8,12 @@ def test_window():
         assert src.window(left, top-src.res[1], left+src.res[0], top) == (
             (0, 1), (0, 1))
 
+
+def test_window_transform():
+    with rasterio.open('tests/data/RGB.byte.tif') as src:
+        assert src.window_transform(((0, src.height), (0, src.width))) == src.affine
+        assert src.window_transform(((0, None), (0, None))) == src.affine
+        assert src.window_transform(((None, None), (None, None))) == src.affine
+        assert src.window_transform(((None, src.height), (None, src.width))) == src.affine
+        assert src.window_transform(((1, None), (1, None))).c == src.bounds.left + src.res[0]
+        assert src.window_transform(((-1, None), (-1, None))).c == src.bounds.left - src.res[0]