Dear FreeSurfers,
I am working on generating a functional map of electrophysiological activity on a freesurfer pial surface and I've come across something that has stumped me. I have the electrode coordinates in RAS space and I am trying to interpolate a value at each surface vertex for the color map using the RAS coordinate of each vertex. However, the RAS coordinates I read into matlab using freesurfer_read_surf.m are different from what is being displayed in tksurfer. (I'm comparing RAS coordinates by hovering the cursor in tksurfer.) Most of the time the differences are very small, but occasionally they can be large. I haven't been able to identify any kind of a constant offset or relationship between these coordinates.
Should the RAS coordinates displayed in tksurfer be the same as what is read directly from the surface file? Is there a better way to approach this task?
Thanks very much for any suggestions.
Regards, Ben Brinkmann
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Benjamin H. Brinkmann, PhD Mayo Systems Electrophysiology Lab Alfred 9-441C, SMH 1216 Second St. SW Rochester, MN 55902