A PermMap is a Mapping which permutes the order of coordinates, and possibly also changes the number of coordinates, between its input and output.
In addition to permuting the coordinate order, a PermMap may also assign constant values to coordinates. This is useful when the number of coordinates is being increased as it allows fixed values to be assigned to any new ones.
For details of additional special values that may be used in this array, see the description of the CONSTANT argument.
For details of additional special values that may be used in this array, see the description of the CONSTANT argument.
Care should be taken to ensure that locations lying outside the extent of this array are not accidentally addressed. The array is not used if the INPERM and OUTPERM arrays do not contain negative values.
AST A Library for Handling World Coordinate Systems in Astronomy