VCG - Critical Points

Description

Searches for critical points in given flow and assigns them a type dependent on sign of real valued eigenvalue. -1 denotes a sink, 1 source and 0 saddle.

Details


Critical Points, points of zero flow velocity, are important characteristics of a flow and potential candidates for vortex cores. This Plugin extracts critical points via a subdivision approach whose critieria is the change in sign in a partition of the underlying flow. The algorithm used in this plugin performs the subdivision on each cell of a uniform grid on the flow.
Given the approximate nature of subdivision schemes, several parameters controlling the precision and termination of the algorithm have to be supplied. Tolerance defines in effect the minimum size of a subdivision holding a potential critical point, while FilterTolerance controls how close critical points need to be apart to be considered seperate. Further, MaxRecursionDepth acts similarily to FilterTolerance, as a recursion depth in each grid cell exceeding this value will lead to a candidate partition being considered a critical point (the critical point is assumed to be in the middle of the candidate partition). Opposed to that, MaxIterationsPerCell limits the overall iterations of the algorithm per cell, leading to critical points from that cell to be marked as degenerate and removed if RemoveDegenerateResults is set.

Input

vtkDataObject

Output

vtkPolyData

Parameters

Name
Description
 Values/Default
Tolerance Minimum length of candidate partition diagonal before to be considered a critical point. 1e-14
FilterTolerance no description available 1e-13
MaxRecursionDepth Maximum recursion depth for each cell on the grid. 200
MaxIterationsPerCell Maximum iteration for each cell on the grid. Set to 0 for automatic choice of this parameter. 0
RemoveDegenerateResults Remove (degenerate) points from cells which have exceeded maximum iterations. 1

Installation Instructions

Authors

Lutz Hofmann

References

J. Jeong, F. Hussain:
On the identification of a vortex
Journal of Fluid Mechanics, vol. 285, pp. 69–94, 1995.

Acknowledgements