vtkDecimatePro - reduce the number of triangles in a mesh
Super Class: vtkPolyDataToPolyDataFilter
Description:
vtkDecimatePro is a filter to reduce the number of triangles in a triangle mesh, forming a good approximation to the original geometry. The input to vtkDecimatePro is a vtkPolyData object, and only triangles are treated. If you desire to decimate polygonal meshes, first triangulate the polygons with vtkTriangleFilter object. The implementation of vtkDecimatePro is similar to the algorithm originally described in "Decimation of Triangle Meshes", Proc Siggraph `92, with three major differences. First, this algorithm does not necessarily preserve the topology of the mesh. Second, it is guaranteed to give the a mesh reduction factor specified by the user (as long as certain contraints are not set - see Caveats). Third, it is set up generate progressive meshes, that is a stream of operations that can be easily transmitted and incrementally updated (see Hugues Hoppe's Siggraph '96 paper on progressive meshes). The algorithm proceeds as follows. Each vertex in the mesh is classified and inserted into a priority queue. The priority is based on the error to delete the vertex and retriangulate the hole. Vertices that cannot be deleted or triangulated (at this point in the algorithm) are skipped. Then, each vertex in the priority queue is processed (i.e., deleted followed by hole triangulation using edge collapse). This continues until the priority queue is empty. Next, all remaining vertices are processed, and the mesh is split into separate pieces along sharp edges or at non-manifold attachment points and reinserted into the priority queue. Again, the priority queue is processed until empty. If the desired reduction is still not achieved, the remaining vertices are split as necessary (in a recursive fashion) so that it is possible to eliminate every triangle as necessary. To use this object, at a minimum you need to specify the ivar TargetReduction. The algorithm is guaranteed to generate a reduced mesh at this level as long as the following four conditions are met: 1) topology modification is allowed (i.e., the ivar PreserveTopology is off); 2) mesh splitting is enabled (i.e., the ivar Splitting is on); 3) the algorithm is allowed to modify the boundary of the mesh (i.e., the ivar BoundaryVertexDeletion is on); and 4) the maximum allowable error (i.e., the ivar MaximumError) is set to VTK_LARGE_FLOAT. Other important parameters to adjust include the FeatureAngle and SplitAngle ivars, since these can impact the quality of the final mesh. Also, you can set the ivar AccumulateError to force incremental error update and distribution to surrounding vertices as each vertex is deleted. The accumulated error is a conservative global error bounds and decimation error, but requires additional memory and time to compute.
Caveats:
To guarantee a given level of reduction, the ivar PreserveTopology must be off; the ivar Splitting is on; the ivar BoundaryVertexDeletion is on; and the ivar MaximumError is set to VTK_LARGE_FLOAT. If PreserveTopology is off, and SplitEdges is off; the mesh topology may be modified by closing holes. Once mesh splitting begins, the feature angle is set to the split angle.
See Also:
Methods:
Detailed Method Descriptions:
| static vtkDecimatePro *New () |
| void SetTargetReduction (float ) |
| float GetTargetReduction () |
| void SetPreserveTopology (int ) |
| int GetPreserveTopology () |
| void PreserveTopologyOn () |
| void PreserveTopologyOff () |
| void SetFeatureAngle (float ) |
| float GetFeatureAngle () |
| void SetSplitting (int ) |
| int GetSplitting () |
| void SplittingOn () |
| void SplittingOff () |
| void SetSplitAngle (float ) |
| float GetSplitAngle () |
| void SetPreSplitMesh (int ) |
| int GetPreSplitMesh () |
| void PreSplitMeshOn () |
| void PreSplitMeshOff () |
| void SetMaximumError (float ) |
| float GetMaximumError () |
| void SetAccumulateError (int ) |
| int GetAccumulateError () |
| void AccumulateErrorOn () |
| void AccumulateErrorOff () |
| void SetBoundaryVertexDeletion (int ) |
| int GetBoundaryVertexDeletion () |
| void BoundaryVertexDeletionOn () |
| void BoundaryVertexDeletionOff () |
| void SetDegree (int ) |
| int GetDegree () |
| void SetInflectionPointRatio (float ) |
| float GetInflectionPointRatio () |
| int GetNumberOfInflectionPoints () |
| void GetInflectionPoints (float *) |
| float *GetInflectionPoints () |