Hi Chris
this probably means that the triangles aren't constructed according to our
conventions. The ordering in faces is important as the cross-product of the
legs of each triangle have to point outwards. That's how we define the
surface normal vector field. Sounds like whatever software you used uses
the oppposite convention. You could try swapping the order of vertices in
the face list
cheers
Bruce
On Fri, 9 Mar 2018, Chris Adamson wrote:
Freesurfer devs,
I have a baffling problem in mris_sphere.
I have generated some surfaces using an external tool that uses VTK. After
converting the surfaces
into freesurfer format using a basic format converter, then adding volume
geometry to the surface
file using the image used to create it the surface appears dark in freeview.
When I do mris_inflate
followed by mris_sphere, mris_sphere says nearly all the triangles have
negative area at the end and
it never finishes. I verified in MATLAB that the surface normals (computed by
mris_convert) of the
original white surfaces point outwards. The darkness in freeview is not fixed
by changing the order
of the indices of the faces (which should invert the normal). I’m at a loss to
explain this.
Thanks in advance,
Chris.
Dr Chris Adamson
Senior Research Officer
Developmental Imaging, Clinical Sciences
Murdoch Childrens Research Institute
The Royal Children’s Hospital
Flemington Road, Parkville, VIC 3052 Australia
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