A value assigned to Card will position the FitsChan at any desired point, so that a particular card within it can be accessed. Alternatively, the value of Card may be enquired in order to determine the current position of a FitsChan.
The default value of Card is 1. This means that clearing this attribute (using astClear) effectively "rewinds" the FitsChan, so that the first card is accessed next. If Card is set to a value which exceeds the total number of cards in the FitsChan (as given by its Ncard attribute), it is regarded as pointing at the "end-of-file". In this case, the value returned in response to an enquiry is always one more than the number of cards in the FitsChan.
AST A Library for Handling World Coordinate Systems in Astronomy