[vtkusers] Streamlines Debugging tips?

[Stewart Dickson]

Hello, List,

I am attempting to compute streamlines through a vector-valued 
structured grid of data points.

Following the example 
VTK/Examples/VisualizationAlgorithms/Tcl/officeTubes.tcl

I find that for my data:
vtkStructuredGridReader reader
[[reader GetOutput] GetLength] = 3.720380
[[reader GetOutput] GetCenter] = 0.000349998 0 0
  maxVelocity [[[[reader GetOutput] GetPointData] GetVectors] 
GetMaxNorm] = 160.003000
maxTime [expr 35.0 * $length / $maxVelocity]
= 0.813818

I am (arbitrarily) scattering 60 (vtkPointSource) random seed points
over a $length/2.0 radius from the center of my data set.

When I run my scri[pt through Vtk, I get the following messages:
ERROR: In /usr/local/src/VTK/Common/vtkPolyLine.cxx, line 101
vtkPolyLine (0x892cfa8): Coincident points in polyline...can't compute 
normals

Warning: In /usr/local/src/VTK/Graphics/vtkTubeFilter.cxx, line 195
vtkTubeFilter (0x80ef9a0): No normals for line!
(Repeated 4 times)
And no geometry displayed in the vtkRenderWindow (OpenGL).

I suspect that vtkStreamLine  Set[Integration]StepLength [0.05]0.5 
is/are wrong for the dimensions of my space and the velocity of my 
vector data.

Will randomly-generated points landing in a region of zero velocity
cause the streamline generator to puke? (Cannot generate normals on 
zero-length segments)

Are there any published rules-of-thumb for setting integration 
parameters appropriate to the data fields under observation?
Are there any resommended methods of debugging the integrator/streamline 
generator?

Thanks,

-Stewart Dickson, Visualization Researcher
Computer Science and Mathematics Division
Oak Ridge National Laboratory
http://www.csm.ornl.gov/~dickson