Sometime, there is a datum shift grid covering a wide area and smaller datum shift grids covering smaller area at finer resolution. Current SIS version does not handle those smaller grids (called "specialization" here). We need a MathTransform implementation which delegate to another transform when the coordinate is found to be in a given area.
This is useful not only for datum shift grids, but also for localization grids (e.g. in GeoTIFF files) when pixel coordinates of control points in the last rows or columns are not spaced in the same way than the first points. This happen in Sentinel 1 images for instance.