I've been struggling to convert a freesurfer surface into an MNI space coordinate. I tried to follow some tutorials and to play around with transformation matrices but nothing works.

I have an MNI surface from freesurfer (the cvs_avg35_inMNI152) and I need to align it to the 3d MNI 152. When loading them with fieldtrip it almost matches as can be seen in the picture https://ibb.co/evkcRb

I would like to apply a transformation to align the surface to the volume.

For the 3d MNI I have the transformation matrix:

-1 0 0 91

0 1 0 -127

0 0 1 -73

0 0 0 1

For the surface I can get the ori.mgz transformation:

-1 0 0 128

0 0 1 -146

0 -1 0 148

0 0 0 1

Could someone point me out how to convert the FS surface into spm coordinates?

Thank you

Dorothy