Re: Slow Irregular3DSet-Constructor

> I'm new with VisAD and not jet very experienced with its mechanisms. I'm
> trying to write an Application for presenting the measured data of a
> satellite in 3D. Therefore I constructed an Irregular3DSet. I have to
> handle with a lot of data. So I tried to construct a Irregular3DSet with
> nearly 5000 datapoints. On a Pentium II-400 System it took about half an
> hour to run the Irregular3DSet-Constructor.
>
> My questions are:
> - Is it normal that the Irregular3DSet-Constructor is that kind of slow?
>
> - Is there another possibility to visualize my data?

The Irregular3DSet constructor is slow because it invokes an
algorithmn for computing the Delaunay tetrahedralization of
your 5000 3-D points, and even the fastest Delauany algorithms
are slow for this task.

However, you only need to do this when you really have a random
set of points in 3-D and do not know a topology for them.

A satellite image generally has a 2-D gridded topology, with a
functional dependency from two independent variables (often called
"line" and "element"), to one or more dependent variables (often
called pixel radiances).  In VisAD we'd say this data has MathType:

  ((line, element) -> (radiance1, ..., radianceN))

This is a FunctionType, and the data would be stored in a
FlatField.

There is a finite sampling of (line, element) space, generally
on some regular 2-D grid.  For that we use a Gridded2DSet as the
domain Set of the FlatField.  If the 2-D grid has regular intervals
of line and element, then you can use a Linear2DSet in place of the
Gridded2DSet.

Check out Ugo Taddei's excellent tutorial on all this, especially
Section 3 on Two-dimensional Sets, at:

  http://www.ssec.wisc.edu/~billh/tutorial/index.html

If your data are not the raw image data, but the product of an
analysis, you may still have some information about the sampling
topology so you can avoid the Delaunay algorithm.  If you have a
known irregular topology, you can construct a DelaunayCustom
object from it, and pass that to the IrregularSet constructor,
avoiding the Delaunay algorithm.

Cheers,
Bill
----------------------------------------------------------
Bill Hibbard, SSEC, 1225 W. Dayton St., Madison, WI  53706
hibbard@xxxxxxxxxxxxxxxxx  608-263-4427  fax: 608-263-6738
http://www.ssec.wisc.edu/~billh/vis.html