Hi Meng,
The grid parent defines the volume space for the output of 3dSurf2Vol, and the number of columns of input data will define the number of volumes to output, which will be of float type. The resulting dataset size should come directly from that.
But still, why are you going back to volume space? If you just want standard space coordinates, do as Peter suggested, and display your results on the standard mesh surface from that space of your choice. Those surface coordinates are already in the given space.
Note that here the transformation between all of the spaces (single subject and template spaces) is done via FreeSurfer's alignment of each to its own template (on the surface).
Anyway, just show your suma results on the MNI152 standard mesh surface.
- rick
