[SciPy-user] Questions about Line Integral Convolution tutorial

Bridgman, William T. William.T.Bridgman@nasa....
Tue Nov 25 08:44:45 CST 2008


I've got a 3-D vector field that separates nicely into toroidal and a  
2-D poloidal component.  I plan to use LIC on the poloidal component  
projected on a slice of the volume.

In the Cabral paper, Section 4.3 mentions a wrapping that can occur if  
the texture is too small.  I'm wondering if the shift I'm seeing may  
be an artifact of the texture dimensions being transposed relative to  
the input vector field.  If the texture doesn't have to be the same  
size as the vector field, it should be an easy fix to get around for  

Part of my dataset also has a parallel flow near the edge which this  
paper mentions can create false singularities.

Thanks for the input.


On Nov 24, 2008, at 10:56 PM, scipy-user-request@scipy.org wrote:
> 2008/11/24 Bridgman, William T. <William.T.Bridgman@nasa.gov>:
>> Is there any protocol for others updating the Wiki entry?  I've just
>> joined Scipy but been a member of AstroPy since its inception - but I
>> have yet to write or update a Wiki page.
> Generally the protocol is "go right ahead, it's version-controlled".
> Just out of curiosity, what were you hoping to use the LIC code for?
>> I'm still getting some type of 'shifting' of my dataset after running
>> LIC, so I need to examine the Cabral reference more closely.  I think
>> I'm still missing something.
> It is totally possible there's a big in my code. In particular David
> Huard pointed out there may be an indexing bug that means that instead
> of integrating forward, it integraes backward twice.
> If the code works right, you shouldn't see any shifting, but Cabral et
> al. point out that it's very important the algorithm and kernel be
> symmetric, or you can get circles turning into spirals and the like.
> Anne

Dr. William T."Tom" Bridgman               Scientific Visualization  
Global Science & Technology, Inc.          NASA/Goddard Space Flight  
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/

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