In this chapter we describe a software code developed by the authors and capable to manipulate the topological structure of apparent contours.
The appcontour package is a free software project hosted on sourceforge.net, its home page is http://appcontour.sourceforge.net/ from where the source code can be downloaded, compiled and installed, following the standard procedure for Unix projects. It contains the executables “contour”, the core of the software, and “showcontour”, the visualization program, a few utilities, mainly in the form of shell scripts, and many examples of apparent contours.
The topological structure of an apparent contour is invariant under smooth deformations of the plane. The software code is devised in such a way to be completely insensitive to the particular embedding in the plane, and only captures such properties as adjacency, relative position, orientation and topological structure of the apparent contour.
