View Dependent Progressive Meshes

The VDPM software is based on "Truly Selective Refinement of Progressive Meshes", J. Kim and S. Lee, In Proc. Graphics Interface 2001.

The library is located in `OpenMesh/Tools/VDPM/` and in `OpenMesh/Apps/VDProgMesh/` are demo applications:

1. `mkbalancedpm` creates balanced progressive meshes
2. `vdpmanalyzer` takes a progressive mesh and generates a view dependent progressive mesh.
3. `vdpmsynthezier` is viewer for vdpm meshes.

Todo:
  Complete VDPM documentation.