Sarah: Freesurfer surface file formats are documented at:
http://grahamwideman.com/gw/brain/fs/surfacefileformats.htm ... including the "W" file format (scroll down). The coordinate system for FreeSurfer's vertices is RAS, described in more detail at: http://grahamwideman.com/gw/brain/fs/coords/fscoords.htm As for: > My main question is this: Do you know how I can convert the > vertex coordinates that I have from my MEG data to the vertex > number that freesurfer uses. Are the vertex numbers part of a > coordinate system that I can then transform between the two systems? Presumably your MEG data provides 3D coordinates in some XYZ space defined by your MEG equipment or software. The transformation between that coordinate system and FS's would need to be known to convert vertex *positions* in one space to the other. In situations where your two types of equipment don't tell you how to ttransform between the two systems (eg: data gathered in entirely different equipment at different times), then you have to perform some sort of registration based on the actual images themselves (or possibly surfaces if that's what you have). If that's your situation then it would certainly be helpful to find someone in your exact same situation in case that might save you from devising it yourself. FS's vertex numbers themselves have meaning only as IDs within the particular subject -- there's no correspondence even across subjects, unless you perform the intersubject surface registration, which results in a cross-reference. (Then the vertex IDs are still subject-specific, but you at least have a cross-reference.) (The above of course goes out the window if, while I was not paying attention, FS has sprouted its own MEG feature that I don't know about!). Hope that helps, Graham _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
