Apply affine transformation, like a *vox2ras_tkr* transformation, to input. This is just matrix multiplication for different input objects.
apply.transform(object, matrix_fun)numerical vector/matrix or Triangles3D instance, the coorindates or object to transform.
a 4x4 affine matrix or a function returning such a matrix. If `NULL`, the input is returned as-is. In many cases you way want to use a matrix computed from the header of a volume file, e.g., the `vox2ras` matrix of the respective volume. See the `mghheader.*` functions in the *freesurferformats* package to obtain these matrices.
the input after application of the affine matrix (matrix multiplication)