Re: Questions about Streamlines, FlowControl, and FlatField.resample()

Hi Olav,

Thank you for the stack dumps with line numbers for your
three Exceptions. It is interesting that all three occur
at line 2357 of ShadowType.java. I think Tom Rink will
take a look at these and get back to you.

> . . .
> This error does not occur if the wrong vector components are used. This
> means, if one vector is perpendicular to the plane (no streamlines can
> be generated). The question is, should this work or is it impossible?

I assume your 3-D data are on an Irregular3DSet and you
resample to a Gridded3DSet with manifold dimension = 2?
When you say 'wrong vector components' do you mean that
you are mapping a RealType to Flow that does not occur in
the MathType of your cut plane, or that does occur but
whose values are always 0? If the latter, then you should
see flow vectors or streamlines that are always aligned with
the axis of the non-zero flow (i.e., the non-zero RealType
mapped to Flow). If the former, then there should probably
be no flow rendering.

> A general question is, are there any ranges for the different options of
> FlowControl? Next i want to know, if there are any plans to extend the
> streamline capabilities of VisAD? If not, then i have to implement it by
> myself.

There are no plans to extend the streamline capabilities of
VisAD. All such plans are driven by our funding sources.

> At least i have a little different question. The 3D example uses
> FlatField.resample() to get the cutplane. If you look at
> error_in_cutplane.png, there is a region left from the colored ball in
> the middle with no vectors. To clarify the problem, i have to say
> something about the data. This is a dataset from a CFD computation. The
> flow arround a ball. within the ball are no points defined. Look at
> Grid_of_cutplane_through_Ball.png. It shows a cut through the original
> grid (unstructured hexahedra). The error with the missing regions only
> occur if the cutplane goes through the empty region and is not the same
> at every time. Sometimes this error is not there. Near the surface it is
> different. There is always an error, regardless of the number of points
> used for the plane (max. tryed 1000x1000). I have tryed all possible
> options for resample(). No changes in output. The question is, if it is
> a general problem of the resample algorithm with this kind of data.

The question is whether this is a problem with resample()
or with flow rendering. If you do the same resample() but
map values to RGB rather than Flow, do you still see the
missing region?

The resample() method has been tested by lots of applications
over the years. There may still be a problem like this, but
I'd need a test case that I can run and that demonstrates
the problem.

Cheers,
Bill