[vtkusers] Stream Tube

[Berk Geveci]

Unfortunately, this is a common problem with the current streamline
filter. There are two different settings which control step length:
1. vtkStreamer:: IntegrationStepLength. This controls the step size
   used in the actual integration and has units of cell length
2. vtkStreamLine:: StepLength. This controls the length of each
line segment in the output. When it is smaller than the 
IntegrationStepLength, interpolation is used to add points. The 
problem is that this setting has units of time. Therefore, where
the magnitude of velocity is small, you will end up with more points,
probably a lot more than there is integration points. However, if you
choose a larger StepLength, you might loose points where the speed is
larger.

The solution ? If using 4.0, play with StepLength until you reach
a compromise. If using a development (nightly) version of VTK, use
vtkStreamTracer. It only has one step length parameter which controls
both the integration points and the actual output and you can specify
which units to use.

-Berk

On Mon, 2002-09-23 at 06:53, James C. Robinson wrote:
> Dear All,
> 
> I am creating a stream tube using a vtkStreamLine object that gets the
> output from reading a file containing a vtkUnstructuredGrid. The model is a
> transient pressure model (flow through porous media) and the flows are
> generated at each point in the (FE) mesh.  The problem that I am having is
> that, depending on where I start the streamline, the PC jams up trying to
> calculate the stream tube. This seems to be related to very small velocities
> at the start point, thus meaning (I suppose) that the steps are tiny (or
> erroneous, if the flow is so small that it is inaccurate due to machine
> error/round off etc.)
> 
> How can I take any flow field and have the stream tube figure out itself
> whether the velocities are going to be too low and whether increasing step
> sizes etc (step lengths or integration step lengths) will help?
> 
> Regards,
>  Jim
> 
> ______________________
> 
> James C. Robinson, PhD,
> Chartered Engineer,
> Kepler Engineering Software Ltd.,
> 42 Rivergrove,
> Glanmire, Co. Cork,
> Eire
> 
> Tel:         +353-21-4822028
> Tel:         +353-87-2393010
> Fax:        +353-21-4822721
> E-mail:     j.robinson at kepler.ie
> ______________________
> 
> 
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