source files: contour.lsp
A `radial contour' is a representation for certain types of 2-D closed polygons. It maintains a local coordinate system and stores vertex positions in polar coordinates. (`r' and `theta', rather than `x' and `y' used in Cartesian coordinates.) Because a radial contour is used as a tool for segmentation, the exact locations of its vertices may be uncertain. Consequently it can also store inner and outer bounds for the `r' value of each vertex. (The `theta' value remains constant for a given vertex.)
This implementation assumes a fixed angle between adjacent vertices. So for each vertex, only the distance from the contour's center is stored; its anglular position can be computed from its position in the array of vertices.