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MNI152 to MNI305 Affine Transform Matrix

Source: R/coordinate_spaces.R
MNI152_to_MNI305.Rd

The inverse of MNI305_to_MNI152, for converting RAS coordinates from MNI152 space back to MNI305 (fsaverage) space.

Usage

MNI152_to_MNI305

Format

A 4x4 numeric matrix (affine transform in homogeneous coordinates).

Details

This matrix is derived from FreeSurfer's mni152.register.dat file, located at $FREESURFER_HOME/average/mni152.register.dat.

The transform accounts for the approximately 4mm difference between MNI305 and MNI152 coordinate systems. It includes small rotation, scaling, and translation components.

To apply: for a point p = c(R, A, S), compute MNI305_to_MNI152 %*% c(p, 1) and take the first 3 elements.

See also

MNI305_to_MNI152, transform_coords

Examples

# Transform a point from MNI152 to MNI305
point_152 <- c(10.695, -18.409, 36.137)
point_305 <- (MNI152_to_MNI305 %*% c(point_152, 1))[1:3]
print(point_305)  # approximately c(10, -20, 35)
#> [1]  10.00091 -20.00261  34.99848