A decoder is configured to decode a bitstream having a block based geometric partition having a plurality of orthogonal block boundaries by assigning a first plurality blocks on one side of an angled line segment a first common motion vector and by assigning a second plurality of blocks on the other side of the angled line segment a second common motion vector different than the first common motion vector. The decoder reconstructs the first plurality of blocks using the first common motion vector and the blocks in the second plurality of blocks using the second common motion vector.