GTS stands for the GNU Triangulated Surface Library. It is an Open Source
Free Software Library intended to provide a set of useful functions to deal
with 3D surfaces meshed with interconnected triangles.

A brief summary of its main features:
   - Simple object-oriented structure giving easy access to topological
     properties.
   - 2D dynamic Delaunay and constrained Delaunay triangulations.
   - Robust geometric predicates (orientation, in circle) using fast adaptive
     floating point arithmetic.
   - Robust set operations on surfaces (union, intersection, difference).
   - Surface refinement and coarsening (multiresolution models).
   - Dynamic view-independent continuous level-of-detail.
   - Preliminary support for view-dependent level-of-detail.
   - Bounding-boxes trees and Kd-trees for efficient point location and
     collision/intersection detection.
   - Graph operations: traversal, graph partitioning.
   - Metric operations (area, volume, curvature ...).
   - Triangle strips generation for fast rendering.

WWW: http://gts.sourceforge.net/