Hi, I have implemented PCA for plane recognition in Visual C++ using standard template libraries. To understand PCA, refer the textbook on Pattern Classification by Duda, Hart and Stork. For an implementation in C, refer Numerical Recipies in C. You'd also find an easy-to use tool in the LA package for Tcl. To use PCA, you need to be familiar with eigen values and what they physically represent and potentially singular value decomposition techniques. Hope this helps, C