add vcglib

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+
+   VCGLib  http://www.vcglib.net 
+    Copyright(C) 2005-2006             
+   Visual Computing Lab  http://vcg.isti.cnr.it          
+   ISTI - Italian National Research Council                 
+   
+
+                                                                       
+This program is free software; you can redistribute it and/or modify      
+it under the terms of the GNU General Public License as published by      
+the Free Software Foundation; either version 2 of the License, or         
+(at your option) any later version.                                       
+                                                                          
+This program is distributed in the hope that it will be useful,           
+but WITHOUT ANY WARRANTY; without even the implied warranty of            
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the             
+GNU General Public License (http://www.gnu.org/licenses/gpl.txt)          
+for more details.                                                 
+
+--- Synopsis ---
+
+`tridecimator fileIn fileOut face_num [opt]`
+
+Tridecimator is a commandline mesh simplifier based on a variant of the quadric error edge collapse strategy. 
+It supports `PLY, OFF, OBJ` format for input and output and require a target number of faces. 
+The following options are supported:
+
+-e# QuadricError threshold  (range [0,inf) default inf) 
+-b# Boundary Weight (default .5) 
+-p# Quality quadric Weight (default .5) 
+-q# Quality threshold (range [0.0, 0.866],  default .3 ) 
+-n# Normal threshold  (degree range [0,180] default 90) 
+-w# Quality weight factor  (10) 
+-E# Minimal admitted quadric value (default 1e-15, must be >0) 
+-Q[y|n]  Use or not Face Quality Threshold (default yes) 
+-H[y|n]  Use or not HardQualityCheck (default no) 
+-N[y|n]  Use or not Face Normal Threshold (default no) 
+-P[y|n]  Add or not QualityQuadric (default no) 
+-A[y|n]  Use or not Area Checking (default no) 
+-O[y|n]  Use or not vertex optimal placement (default yes) 
+-S[y|n]  Use or not Scale Independent quadric measure(default yes)  
+-B[y|n]  Preserve or not mesh boundary (default no) 
+-T[y|n]  Preserve or not Topology (default no) 
+-W[y|n]  Use or not per vertex Quality to weight the quadric error (default no) 
+-C       Before simplification, remove duplicate & unreferenced vertices 
+    
+
+This simplification tool employ a quadric error based edge collapse iterative approach. 
+Each possible collapse is scored taking into account
+- its quadric error
+- its quadric boundary error
+- the normal variation caused by the collapse itself
+- the future quality (aspect ratio) of the triangles involved in the collapse
+
+The simplification can ends when the desired number of triangles has been reached.
+
+The 'Safe Heap Update' change the set of edges re-inserted in the heap
+after a collapse resulting in a vertex v; this option put back in the
+heap not only incident in the v, but all the edges of the triangles incident
+in v. It slows down a lot.
+
+The 'Scale Independent quadric' is useful when you want simplify 
+two different meshes at the same 'error'; otherwise the quadric 
+error used in the heap is somewhat normalized and independent 
+of the size of the mesh.
+
+The Normal threshold avoid to make large changes in variation of the normal
+of the surfaces, but on the other hand it prevent the removal of small 'folded'
+triangles that can be already present. Therefore in most cases is not very useful.
+
+Cleaning the mesh is mandatory for some input format like STL that always
+duplicates all the vertices.
+
+
+