"of adjacent pixels selected from an initial NDF. The routine divides the original NDF logically into a series of such blocks, each of which does not exceed a specified maximum number of pixels in each dimension. The routine
’s IBLOCK argument allows one of these blocks to be selected; an NDF section for it is then returned.
This routine is intended to allow NDFs to be processed in smaller pieces by selecting successive blocks, each of which may then be processed individually. Note that in general not all the blocks selected from an NDF will have the same shape or size, although none will exceed the specified maximum number of pixels in each dimension.
Corresponding blocks 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 maximum dimension sizes supplied (NDIM) is less than this number, then a value of 1 will be used for the extra dimension sizes. If the value of NDIM is larger than this number, then the excess dimension sizes will be ignored.
If the number of the requested block (IBLOCK) exceeds the number of blocks 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 blocks have been processed. The NDF_NBLOC routine may also be used to determine the number of blocks 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.