The routine NDF_ACRE is provided to assign default values to all of an NDF's axis arrays, thereby defining a default axis coordinate system, as follows:
CALL NDF_ACRE( INDF, STATUS )
If the axis coordinate system is already defined, then all the axis centre arrays will already have values, so this routine will return without action. However, if this coordinate system (and hence each axis centre array) is undefined, then NDF_ACRE will assign default values to all the centre arrays, effectively defining a default axis coordinate system which is equal to the NDF's pixel coordinate system (§).
After this operation, the values available from any of the NDF's
axis components will be unchanged.
This is because the NDF_ system would provide these same axis
centre values as defaults in any case.
Nevertheless, the definition of a default axis coordinate system is
a significant step because it effectively takes a ``copy'' of the current
pixel coordinate system.
Any operation which subsequently changes the NDF's pixel indices
(e.g. the application of pixel-index shifts - see
then affect the pixel centre values, whereas previously it would