Graphics Gems III (IBM Version)

1.6

GENERATING ISOVALUE CONTOURS FROM A PIXMAP

Tim Feldman,     Island Graphics Corporation, San Rafael, California

Publisher Summary

This chapter presents an algorithm that follows the edge of a contour in an array of sampled data. It discusses Freeman chain encoding to produce a list of vectors that describe the outline of the contour. The algorithm is capable of handling contours containing a single sample point, contours surrounding regions of a different elevation, contours that do not form closed curves, and contours that form curves that cross themselves, forming loops. In all cases, it follows the outermost edge of the contour. Given an initial point in an elevation contour in the array, the algorithm finds the edge of the contour. ...