A CONNECTED SET ALGORITHM FOR THE IDENTIFICATION OF SPATIALLY CONTIGUOUS REGIONS IN CRYSTALLOGRAPHIC ENVELOPES

A simple algorithm is described for the identification of spatially co ntiguous regions in crystallographic envelopes. In a single pass throu gh the grid points of the envelope map, the occupied points are assign ed to a series of locally contiguous sets based on consideration of th e connections within single voxels. A spatially contiguous region is i dentified as the union of all of the locally contiguous sets that shar e an element in common. Therefore, chains of spatial connectivity are traced implicitly by performing simple set operations. This algorithm has been implemented in the program CNCTDENV as part of the DEMON/ANGE L suite of density-modification programs.