16. Appendix A – VTK Usage¶
VTK (the Visualisation Toolkit; http://www.vtk.org/) is a an open-source, freely available software system for 3D computer graphics, image processing and visualisation. SPIERSview makes use of VTK version 8.1 for some data-processing purposes (although not for visualisation, which uses custom code to increase speed and memory efficiency). Certain VTK classes used are documented here, where knowing details of algorithms used may help a user understand exactly what SPIERSview is doing with their data. Interested users are referred to the VTK documentation to interpret the notes below.
16.2. Fidelity Reduction¶
SPIERSview default ‘fast and safe’ fidelity reduction uses the vtkDecimatePro filter. AccumulateError is set to ‘off’, PreserveTopology is set to on; no other settings are changed from defaults.
SPIERSview ‘Quadric’ fidelity reduction uses the vtkQuadricDecimation filter. No settings are changed from defaults.
16.3. Island Removal¶
Island removal uses the vtkPolyDataConnectivityFilter class. ColorRegions is set to off; no other settings are changed from defaults. ‘All’ mode uses SetExtractionModeToLargestRegion; otherwise the filter is run in SetExtractionModeToAllRegions mode. Tiny, Small, Medium and Large settings remove regions of up to 20, 100, 600 and 4000 triangles in size respectively.
Smoothing uses multiple passes of the vtkWindowedSincPolyDataFilter filter. FeatureEdgeSmoothing, BoundarySmoothing, GenerateErrorScalars and GenerateErrorVectors are set to off, and PassBand is set to 0.05. Very Weak, Weak, Medium, Strongish, Strong, and Strongest settings use 5, 10, 20, 40, 60, and 100 iterations respectively.
16.5. STL reader¶
SPIERSview uses the vtkSTLreader class to import STL triangle meshes during VAXML import; its restrictions and capabalities are thus those of this VTK class.
16.6. PLY reader¶
SPIERSview uses the vtkPLYreader class to import PLY triangle meshes and surface colour information during VAXML import; it’s restrictions and capabalities are thus those of this VTK class; in particular colour information input is restricted to ‘red’, ‘green’ and ‘blue’ properties of vertex elements.