C program for automatic contouring of spherical orientation data using a modified Kamb method

Abstract

Kamb's method for contouring density diagrams is a simple technique for the preliminary analysis and comparison of orientation data distributions. The method is based on the departure from a uniform distribution, and, unlike the Schmidt method, the dependence of contours on sample size is limited. Several improvements can be made, particularly with regard to the implementation of automatic contouring. To reduce smoothing, the expected count for a random sample drawn from a uniform distribution can be decreased. This gives more localized density estimates that can improve the resolution of features. Density estimates are done directly on the sphere for accuracy. This also permits contouring on stereographic and other nonequal area projections, and accommodates vectorial data. Weighting functions provide better density estimates and increase the smoothness of contour lines. These concepts are implemented in the C program Sphere Contour. Options include selection of data rotation, linear or planar data, equal area or stereographic projection, upper or lower hemisphere, and scatter diagrams. Graphics output is either to the screen (MS-DOS) or to a computer-aided drafting file (AutoCAD DXF). The program is modified easily for other computer systems and graphics devices.