[caret-users] Re: Surface Normals

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


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  

John Harwell
john at brainvis.wustl.edu

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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