SSPX: A program to compute strain from displacement/velocity data

SSPX is a Macintosh, Cocoa/Universal application to compute strain from displacement/velocity data in two and three dimensions. SSPX solves small and large deformation problems, in either the undeformed (Lagrangian) or deformed (Eulerian) configuration. The program offers several options to compute strain: best fit for all or selected data, strain at a point, strain at stations, Delaunay, grid-nearest neighbor, and grid-distance weighted. Except for the strain at stations option in 3D, the program computes the strain on a surface that is either flat (slice) or that follows the topography of the data. In the case of a slice and in 3D, the location and orientation of the slice can be varied to visualize the strain along horizontal or vertical east–west, north–south sections. SSPX plots strain in a 2D view (3D strain is displayed as stereonets). We show the application of the program to GPS data, analogue and DEM mechanical simulations.