[caret-users] Re: Surface Normals

John Harwell john at brainvis.wustl.edu
Wed Jun 6 08:29:25 CDT 2007


Alon,

The surface normals are not stored in a file.  For each coordinate  
file that is loaded into Caret, the normals are computed using the  
coordinates and the topology file associated with the coordinate file.

Normals are computed as follows:
* Compute the normal vector for each triangle in the surface
* For each node, assign it a normal vector that is the average of the  
normal vectors of the triangles that use the node
* Convert each node's normal to a unit vector (length equals 1.0)

If you want to see the values of the normal vectors, use File Menu- 
 >Export File and write a surface as either a VTK surface file or a  
VRML file.  Both of these files include coordinates, surface normals,  
and topology.  Simply search one of these files for the characters  
"Normal".

----------------------------------------------------------
John Harwell
john at brainvis.wustl.edu
314-362-3467

Department of Anatomy and Neurobiology
Washington University School of Medicine
660 S. Euclid Ave.    Box 8108
St. Louis, MO 63110   USA

On Jun 6, 2007, at 5:31 AM, Alon Keren wrote:

> Hello,
>
> I would like to extract from CARET a list of normals to the  
> cortical surface at each node. I saw that CARET can show these  
> normals (Display Control window --> Page Selection list --> Surface  
> Miscellaneous --> Show Normals checkbox). Are these data stored in  
> a specific file, or are the normals computed from the topography  
> file? Where are they stored or how are they computed?
>
> Thanks,
> Alon.
>
>
>
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