The task of transforming from CHIPCOORD to sky coordinates is complicated by the fact that the spacecraft attitude is not fixed but rather `wanders' somewhat over the course of an exposure. The projection from CHIPCOORD to sky coordinates over a period of time can therefore only be estimated by a sequence of transform samples, weighted by the duration of validity of the sample. The user has the facility to supply a dataset table containing a list of spacecraft attitude samples plus the boundary times between them. (The format of this list is described more fully in section 8. See also the task documentation for attbin and the library binned_att.) Each chip image is then subjected to multiple transforms, one per attitude bin; the output image consists of a weighted sum of these transformed images. There are various ways in which the user can specify the weights.