[vtkusers] vtkCellLocator

[James A Galbraith/GALBJA/CC01/INEEL/US]

Good morning everyone.

We are modelling radar beams over terrain using vtk with java.  In order to
mask the radar beams where they intersect the terrain we need to determine
where this intersection occurs.  We are currently using the vtkCellLocator
class with mixed results.  For the most part, we are receiving what we
consider valid intersections, but occasionally we receive intersections
that are not correct.  In some instances the intersection comes at the back
side of a hill the radar beam is "passing through" rather than the front
edge.  In other instances, the beam is allowed to pass through several
hills, intersecting on , say, the third hill.  Instances where the beam is
allowed to pass through several intersections before arriving at the "best"
intersection are very consistent and are always returned this way.  When we
overlay radar beams on the terrain, the terrain then masks the radar beam
wherever it is above the beam - which supports our view that we are getting
invalid intersections from vtkCellLocator.

Can anyone shed some light on how the vtkCellLocator works and why it
possibly is obtaining a "best" cell which is incorrect as far as we are
concerned?  Are we using the correct class for detecting these locations,
or is there another class we should look at?

I tried tweeking the tolerance value, but after looking at the source it
doesn't appear to be used.

Thanks again for all your help

James Galbraith
Idaho national Engineering & Environmental Laboratory (INEEL)
Bechtel BWXT Idaho, LLC
P.O. Box 1625
Idaho Falls, ID  83415-3779
Email: galbja at inel.gov