On Mon, Nov 24, 2008 at 11:46 AM, Bridgman, William T. <William.T.Bridgman@nasa.gov> wrote:

Hello,

I found the Line Integral Convolution (LIC) example very timely for a
project I'm working on.

http://www.scipy.org/Cookbook/LineIntegralConvolution

Once Cython & Pyrex were installed, the demo ran out of the box.
Excellent.

However, now I'm trying to apply this to a different dataset and the C
component is crashing with index errors. I suspect these are being
caused by the fact that my dataset is not a square array.

An examination in the .pyx file has a couple of locations where the
array indices appear to be transposed between x,y vs i,j. I'm not
sure if this is a bug or not. The high symmetry of the demo vector
field would probably not reveal this if it were a bug.

So my questions for the author of the code or the list are:

1) Is there a paper or other reference for the algorithm implemented
here? My searches have revealed several types of LIC
implementations. It would be nice if this were in code comments or at
least on the tutorial page.

I am not sure which paper Anne has used, but I have found

Cabral, Brian and Laeith Leedom. Imaging vector fields using line integral
convolution. SIGGRAPH '93: Proceedings of the 20th annual conference on
Computer graphics and interactive techniques, pages 263-270, 1993.

a very useful reference.

2) Is the algorithm, the demo code, or LIC in general, restricted to
square arrays?

Not that I know of. I have used it on rectangular arrays and it's working, although you may need to transpose the texture array to get it to work.

3) Is there a pure-python or numpy-only (no Cython or Pyrex
requirement) implementation?

Not that I know of. However, with Anne's consent, I have created a scikit named vectorplot using the code she posted in the cookbook. This can be installed with a simple
python setup.py install
It's still not pure python, but you won't need Cython to compile the extension. I've added docstrings, a bit of documentation and utiliy functions to generate kernels that I use to "animate" vector fields.

You can check out the code with subversion at http://svn.scipy.org/svn/scikits/trunk/vectorplot, but bear in mind that the user interface might change.

HTH,

David

Thanks,
Tom
--
Dr. William T."Tom" Bridgman Scientific Visualization
Studio
Global Science & Technology, Inc. NASA/Goddard Space Flight
Center
Email: William.T.Bridgman@nasa.gov Code 610.3
Phone: 301-286-1346 Greenbelt, MD 20771
FAX: 301-286-1634 http://svs.gsfc.nasa.gov/

_______________________________________________
SciPy-user mailing list
SciPy-user@scipy.org
http://projects.scipy.org/mailman/listinfo/scipy-user