In dealing with such tasks as inter- and intra-subject registration both within and across imaging modalities, the concept of transformations between different coordinate systems arises. A module is provided to handle both linear (affine) and non-linear transformations, and to provide input and output in a standardized Brain Imaging Centre format, usually to filenames with the extension .xfm.
To support these functions, two structure types are provided. The first (Transform) is a four by four linear (affine) transform, which facilitates rigid transformations, consisting of scaling, rotation, translation, and shearing. The second is a higher level transform (General_transform), which represents either a linear transform, a non-linear transform (thin-plate spline), a user definable transform, or a concatenation of two or more of these.