The pixel-index bounds of an NDF may be altered when required by explicitly setting them to new values using the routine NDF_SBND. The dimensionality of the NDF may also be changed at the same time. For instance:
INTEGER NDIM, LBND( NDIM ), UBND( NDIM ) ... CALL NDF_SBND( NDIM, LBND, UBND, INDF, STATUS )
will change an NDF's dimensionality to the value specified by the NDIM argument, and set its lower and upper pixel-index bounds to the values specified in the LBND and UBND arrays. When an NDF's shape is changed in this way, the pixel values of any array component which is in a defined state may be affected, as follows:
In cases where the dimensionality of the NDF also changes, the association between pixel indices before and after the change is established in the same way as when creating NDF sections (see §), i.e. by padding the bounds with 1's to match the dimensionalities.
Note that altering the shape of an NDF section using NDF_SBND is a relatively inexpensive operation which merely involves changing the shape of the ``window'' into the NDF which the section describes. In contrast, altering the shape of a base NDF causes changes to be made to the actual data structure and can take considerably longer, especially if one or more of the NDF's array components are in a defined state and contain values which may need to be shuffled to accommodate the change. Consequently, if the values of any array components need not be retained, they should be reset to an undefined state before changing the shape of a base NDF. For instance:
CALL NDF_RESET( INDF, 'Data,Variance,Quality', STATUS ) CALL NDF_SBND( NDIM, LBND, UBND, INDF, STATUS )
would ensure that no array values are retained and that no time is
unnecessarily wasted as a result.