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third/OpenMesh/Doc/decimater.docu

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+//-----------------------------------------------------------------------------
+
+/** \page decimater_docu Mesh Decimation Framework
+
+  The mesh decimation framework has 3 building blocks.
+
+  -# \ref DecimaterAlg
+  -# \ref DecimaterMod
+  -# \ref DecimaterHnd
+
+\section DecimaterAlg The decimation algorithm
+
+  The decimater (OpenMesh::Decimater::DecimaterT) provides the
+  decimation algorithm, while the decimation modules provide the
+  computational part. The modules compute a priority value due to some
+  error metric, which is used by the decimater to feed a priority
+  queue. The lower the error value, the more a potential collapse
+  moves to the front of the queue. The one with the lowest error will
+  always be the candidate for the next collapse.
+
+  This implementation does a halfedge collapse, hence simply
+  collapsing one vertex into another connected by a halfedge.
+
+  \note The decimater ignores all 'locked' and 'deleted' vertices (see
+  OpenMesh::Attributes::StatusBits) 
+
+  \attention The decimater sets temporarily the status bit 'tagged' and
+  clears it after usage regardless of a previous state.
+
+\section DecimaterLock Block vertices from beeing touched by the Decimater
+  You could mark vertices as locked, which should not be modified by the decimater.
+
+  \code
+    // That might be already requested
+    mesh_->request_vertex_status();
+
+    // Get an iterator over all halfedges
+    Mesh::HalfedgeIter he_it, he_end=mesh_->halfedges_end();
+
+    // If halfedge is boundary, lock the corresponding vertices
+    for (he_it = mesh_->halfedges_begin(); he_it != he_end ; ++he_it)
+      if (mesh_->is_boundary(*he_it)) {
+         mesh_->status(_mesh->to_vertex_handle(*he_it)).set_locked(true);
+         mesh_->status(_mesh->from_vertex_handle(*he_it)).set_locked(true);
+      }
+  \endcode
+
+\section DecimaterMod Decimating Modules
+
+  The vertex to be removed is determined by a decimation module, which has
+  to be derived from OpenMesh::Decimater::ModBaseT. The framework
+  supplies already a few decimation modules. But it's very easy to build
+  your own (\ref OpenMesh::Decimater::ModBaseT).  The most important
+  function of a decimation module is
+  OpenMesh::Decimater::ModBaseT::collapse_priority(). It takes an
+  OpenMesh::Decimater::CollapseInfoT describing a potential halfedge
+  collapse, and returns a value due to some error metric. The error
+  value is used by the decimater to feed a priority queue. Collapses
+  with low error will be executed first, and those with large error
+  later. Of course a module computing the error quadric is provided
+  (OpenMesh::Decimater::ModQuadricT).
+
+  This framework allows to use more than one decimation module with
+  some restrictions. Since the error value is always normalized and
+  sometimes very difficult to compare to other metrics, the framework
+  allows only one non-binary module, i.e. a module computing a float
+  value. Every further module must be a binary module,
+  i.e. collapse_prioerity() returns
+  OpenMesh::Decimater::ModBaseT::LEGAL_COLLAPSE or
+  OpenMesh::Decimater::ModBaseT::ILLEGAL_COLLAPSE. In the algorithm
+  the binary modules are evaluated first. If the evaluated collapse
+  passes the test, then the non-binary module contributes to the
+  decision step.
+
+  In some cases the module does not contribute anything to the
+  decision engine of the decimater, but instead, e.g. simply collects
+  information, while the decimater does it's work. For instance the
+  module OpenMesh::Decimater::ModProgMeshT collects information from
+  all collapses that have been done. This information can be used to
+  generate progressive meshes as described in "Progressive meshes",
+  Hoppe, 1996.
+    
+  Provided decimation modules(Binary: B, Continuous: C, Special: X):
+ 
+  - OpenMesh::Decimater::ModAspectRatioT (B,C)
+  - OpenMesh::Decimater::ModEdgeLengthT (B,C)
+  - OpenMesh::Decimater::ModHausdorffT (B)
+  - OpenMesh::Decimater::ModIndependentSetsT (B)
+  - OpenMesh::Decimater::ModNormalDeviationT (B,C) 
+  - OpenMesh::Decimater::ModNormalFlippingT (B)
+  - OpenMesh::Decimater::ModProgMeshT (X)
+  - OpenMesh::Decimater::ModQuadricT (B,C)
+  - OpenMesh::Decimater::ModRoundnessT (B,C)
+
+\section DecimaterHnd Module Handles
+
+  Similar to properties the modules are represented outside the
+  decimater by module handles. Before using the decimater a
+  non-binary module must be registrated with the decimater.
+
+  See \ref DecimaterExa.
+        
+\section DecimaterExa Basic Setup
+
+  The following small example show the basic steps to setup up a
+  decimater:
+
+\include decimater.cc
+
+*/
+