How to calculate the normal of a vertex?

[mingrui]

Hello,

Thanks for this awesome software! I have two questions:

1. How is the normal of a vertex calculated in BrainVISA?
2. How can I generate a split brain surface with cerebellum? That is the hemispheric cerebrum with half cerebellum.

Thank you in advances.

[riviere]

Hi,

1. In a mesh the normal to a vertex can be specified arbitrarily (for OpenGL rendering), but it is normally computed as the average of the normals of the triangles involving a vertex, maybe weighted by each triangle surface (I don't remember exactly, I can check).

2. We don't have a procedure to split the cerebellum hemispheres, nor to separate the cerebellum from the brain stem in Morphologist. The millimetric resolution of standard MRI images does not allow to study the cerebellum grey/white matters and folding efficiently so we have not focused our methods on the cerebellum...
You may obtain a mesh of the cerebellum+stem using the AimsMesh or AimsMeshBrain commands in BrainVisa (after perhaps a little thresholding of the split segmentation image to select the cerebellum+stem part), but not the cerebgellum hemispheres, nor the G/W interface of the cerebellum.

Denis

[mingrui]

Denis, thanks for your reply.