Shape Context Error By Calculating Distance Of Two Different Shapes

In short form, I want to compare different road markings by 'shape context' matching. My first question you can see under: Matching shapes of road marking from OpenData I solved my

Solution 1:

Ok, I think the problem was, that a and b or a and c don't have the same height of pixels (a: 131 x 32px, b / c: 29 x 18 px). When I change the size of the image of b or c to a higher resolution like 131 x 81 px the error disappear and the distance of "shape context" is being computed.