[vtkusers] Possible vtkOBBTree bug or weirdness

[Andrew Parker]

Hi,

So I've been having some problems with vtkOBBTree using the
intersectWithLine method with the following signature:

int IntersectWithLine (double a0[3], double a1[3], double tol, double &t,
double x[3], double pcoords[3], int &subId, vtkIdType &cellId,
vtkGenericCell *cell)

In particular, depending on what I have initialised some of the input
parameters to, which I had assumed and the code and docs indicate their
initial values are not important, with exception of a0, a1, and tol(0,0), I
got different results.  Having looked at the tree, I found that I had
forgotten to set the tolerance, it was undefined in the class and unset.
(might be good if a sensible default got set, this too could be defined as
a bug...)  Anyway, correcting that and setting the tolerance to zero I then
got this:

Percentage Complete: 2Generic Warning: In VTK/Common/vtkMath.cxx, line 736
vtkMath::Jacobi: Error extracting eigenfunctions

A lot.  Looking at the code, the following comment is a bit worrying:

  //// this is NEVER called
  if ( i >= VTK_MAX_ROTATIONS )
    {
    vtkGenericWarningMacro(
       "vtkMath::Jacobi: Error extracting eigenfunctions");
    return 0;
    }

I need a locator that can let me intersect with a line, and given me back:
1) the cell that it intersected with,
2) the location of the intersection.

Also I found in some instances 't' was bigger than one, which I understood
to not be possible.....

Any help, and advice on an alternative intersector that can give me back
the above would be great as my choice of vtkobbtree was almost random....

Cheers,
Andy
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