Threaded implementation of the 3D Surface Nets isocontouring algorithm

Surface Nets is an algorithm used to isocontour segmented 3D volumes. The segmentation is represented by a label map which classified each voxel as inside a segmented region, or as part of the background. One or more labeled regions can be extracted simultaneously. The algorithm also includes a constrained smoothing process to produce higher-quality results. The algorithm is threaded using concepts from Flying Edges (which processes data independently on an edge-by-edge basis).