vtkAbstractInterpolatedVelocityField

Section: Visualization Toolkit Filtering Classes

Usage

vtkAbstractInterpolatedVelocityField acts as a continuous velocity field by performing cell interpolation on the underlying vtkDataSet. This is an abstract sub-class of vtkFunctionSet, NumberOfIndependentVariables = 4 (x,y,z,t) and NumberOfFunctions = 3 (u,v,w). With a brute-force scheme, every time an evaluation is performed, the target cell containing point (x,y,z) needs to be found by calling FindCell(), via either vtkDataSet or vtkAbstractCelllocator's sub-classes (vtkCellLocator & vtkModifiedBSPTree). As it incurs a large cost, one (for vtkCellLocatorInterpolatedVelocityField via vtkAbstractCellLocator) or two (for vtkInterpolatedVelocityField via vtkDataSet that involves vtkPointLocator in addressing vtkPointSet) levels of cell caching may be exploited to increase the performance.

For vtkInterpolatedVelocityField, level #0 begins with intra-cell caching. Specifically if the previous cell is valid and the next point is still in it ( i.e., vtkCell::EvaluatePosition() returns 1, coupled with newly created parametric coordinates & weights ), the function values can be interpolated and only vtkCell::EvaluatePosition() is invoked. If this fails, then level #1 follows by inter-cell search for the target cell that contains the next point. By an inter-cell search, the previous cell provides an important clue or serves as an immediate neighbor to aid in locating the target cell via vtkPointSet:: FindCell(). If this still fails, a global cell location / search is invoked via vtkPointSet::FindCell(). Here regardless of either inter-cell or global search, vtkPointLocator is in fact employed (for datasets of type vtkPointSet only, note vtkImageData and vtkRectilinearGrid are able to provide rapid and robust cell location due to the simple mesh topology) as a crucial tool underlying the cell locator. However, the use of vtkPointLocator makes vtkInterpolatedVelocityField non-robust in cell location for vtkPointSet. For vtkCellLocatorInterpolatedVelocityField, the only caching (level #0) works by intra-cell trial. In case of failure, a global search for the target cell is invoked via vtkAbstractCellLocator::FindCell() and the actual work is done by either vtkCellLocator or vtkModifiedBSPTree (for datasets of type vtkPointSet only, while vtkImageData and vtkRectilinearGrid themselves are able to provide fast robust cell location). Without the involvement of vtkPointLocator, robust cell location is achieved for vtkPointSet.

To create an instance of class vtkAbstractInterpolatedVelocityField, simply invoke its constructor as follows

  obj = vtkAbstractInterpolatedVelocityField

Methods

The class vtkAbstractInterpolatedVelocityField has several methods that can be used. They are listed below. Note that the documentation is translated automatically from the VTK sources, and may not be completely intelligible. When in doubt, consult the VTK website. In the methods listed below, obj is an instance of the vtkAbstractInterpolatedVelocityField class.