How to extract coordinates of irregular border lines from an image file

I have detected border lines of some geometric shapes(combination of thick lines, rectangles and segmentation of circular shapes) and save it as another image file by using PIL. I wonder how can I extract coordinates of the border lines? I want to use this information to construct 2D finite element model for numerical calculation.

Actually, what I'd like to do is to convert an image file to CAD-like files(e.g., iges, sat) or finite element model for mesh generation.

Any help on this subject would be greatly appreciated, thanks!