The routine returns an identifier for an NDF section describing a "chunk" of contiguous pixels selected from an initial NDF. The routine divides the initial NDF logically into a series of such chunks, each of which follows immediately on from the previous chunk, and each of which contains no more than a specified maximum number (MXPIX) of contiguous pixels. The routine’s ICHUNK argument allows one of these chunks to be selected; an NDF section for it is then returned.

CALL NDF_CHUNK( INDF1, MXPIX, ICHUNK, INDF2, STATUS )

INDF1 = INTEGER (Given)

MXPIX = INTEGER (Given)

ICHUNK = INTEGER (Given)

INDF2 = INTEGER (Returned)

STATUS = INTEGER (Given and Returned)

• This routine is intended to allow large NDFs to be processed in smaller pieces by selecting successive chunks, each of which may then be processed individually. Note that in general not all the chunks selected from an NDF will have the same size, although none will contain more than the specified maximum number of pixels.

• Corresponding chunks selected from different NDFs (or NDF sections) with identical shapes will themselves have identical shapes and will contain the same number of pixels.

• All NDF sections obtained via this routine have the same number of dimensions as the input NDF.

• If the number of the requested chunk (ICHUNK) exceeds the number of chunks available in the NDF, then a value of NDF__NOID will be returned for the INDF2 argument (but no error will result). This condition may be used to terminate a loop when all available chunks have been processed. The NDF_NCHNK routine may also be used to determine the number of chunks available.

• If this routine is called with STATUS set, then a value of NDF__NOID will be returned for the INDF2 argument, although no further processing will occur. The same value will also be returned if the routine should fail for any reason.

• The NDF__NOID constant is defined in the include file NDF_PAR.