This openscad work consists of:
1. updated tracing of a colored line in a image, constructing the list of
points along the line.
2. deciding if points are inside or outside of an arbitrary polygon. Well
mostly arbitrary, no holes allowed.
3. mapping an image and cutting the image by the polygon, and
4.using the excellent nSplines library to construct a single polyhedron of
the resulting polygon outlined image.
Yes there are other ways to get this same result. But I wanted to do more
with image processing beyond surface().