Hi everyone,

I need to create the vector normal to the surface at each “white” vertex.

I would like to end up with 7 fields in each entry:

1 Vertex number

2-4  RAS coordinates

5-7 RAS components of the normal vector pointed from ctx à wm

mri_annotation2label gets me the first 4.

I just don’t want to reinvent the wheel getting the normal.

If there’s a way to get freesurfer to kick out the normals, that would be best.

Here are naïve questions that arise out of this problem:

1. Is there a simple way to identify which vertices are “nearest neighbors” other than measuring and sorting the distances between each and all the others i.e. which ones form a triangle?  I understand to use the normalized average of the 6 triangles which include the vertex.

2. Is there a simple way to identify the order of the sides of each triangle so that their cross product is ordered correctly to produce ctx à wm?

Thanks for your help with this.

Don