vox2ras_tkr: The FreeSurfer default vox2ras_tkr matrix.

In fsbrain: Managing and Visualizing Brain Surface Data

The FreeSurfer default vox2ras_tkr matrix.

Description

Applying this matrix to a FreeSurfer CRS index of a conformed volume will give you the RAS coordinates of the voxel in surface coordinates, i.e., in the coordinates used in surface file like lh.white. The central voxel is 127,127,127 when using zero-based indices (or 128,128,128 when using one-based indices), meaning its surface RAS coordinates are 0.0, 0.0, 0.0. The returned matrix is the inverse of the ras2vox_tkr matrix.

Usage

vox2ras_tkr()

Value

numeric 4x4 matrix, the FreeSurfer vox2ras_tkr matrix.

See Also

Other surface and volume coordinates: ras2vox_tkr()

Examples

   # Compute surface RAS coordinate of voxel with CRS (0L, 0L, 0L):
   vox2ras_tkr() %*% c(0, 0, 0, 1);
   # Show that voxel with CRS (128,128,128) is at the
   #  origin (0.0, 0.0, 0.0) of the surface RAS coordinate system:
   (vox2ras_tkr() %*% c(128, 128, 128, 1))[1:3];

fsbrain documentation built on Aug. 23, 2026, 5:06 p.m.