added assertion

geo.coord_calc.calc_FullDataset_corner_positions():
- added input assertion

ptds/geo/coord_calc.py

@@ -41,6 +41,10 @@ def calc_FullDataset_corner_positions(mask_1bit, assert_four_corners=True, algor
     :return:                        [UL, UR, LL, LR] as [(ULrow,ULcol),(URrow,URcol),...]
     """
 
+    pixVals = np.unique(mask_1bit)
+    assert True in pixVals or 1 in pixVals, 'According to the given mask the mask extent is completely outside the ' \
+                                            'image. No calculation of image corner coordinates possible.'
+
     rows, cols = mask_1bit.shape[:2]
 
     if sum([mask_1bit[0,0], mask_1bit[0,cols-1], mask_1bit[rows-1,0], mask_1bit[rows-1,cols-1]]) == 4: