Your interpretation is not correct. RAS always means that R is pos x, A is pos y, and S is pos z.
That is the voxel-to-RAS transform. Here voxel means column-row-slice. So this matrix takes a col, row, slice and converts it into a RAS. So that first negative 1 means that as the column number increases the R decreases (ie, becomes more leftward) Look at our wiki http://surfer.nmr.mgh.harvard.edu/fswiki/CoordinateSystems for more info doug On 06/23/2014 01:44 PM, Arman Eshaghi wrote: > Hi, > > I'm trying to understand the conversion from RAS (freesurfer surface > coordinate) to volume space (x, y, and z.. According to Graham Wideman > documentation here > http://www.grahamwideman.com/gw/brain/fs/coords/fscoords.htm (if it is > not outdated), Right is negative x, *Anterior is positive z*, and > *Superior is positive y*. > > Just to double check, usign mri_info on a sample T1.mgz in one subject > I get this ras to voxel transform: > > -1 0 0 126.944 > 0 0 -1 135.16 > 0 1 0 110.6 > 0 0 0 1 > > Assuming we have correctly set the (0, 0, 0), and we can extract R A > and S (respectively) coordinates using C++ or Python code it means: > Right is negative x, *Anterior is negative z*, and *Superior is > positive y* (conflicting coordinates are in vold). Am I missing > anything here, or coordinate systems have changed from the probably > outdated documentation? Thanks in advance for any input on this rather > confusing point. > > All the best, > Arman > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer The information in this e-mail is intended only for the person to whom it is addressed. If you believe this e-mail was sent to you in error and the e-mail contains patient information, please contact the Partners Compliance HelpLine at http://www.partners.org/complianceline . If the e-mail was sent to you in error but does not contain patient information, please contact the sender and properly dispose of the e-mail.
