sds_id	IN:	Data set identifier returned by SDcreate or SDselect
	origin	IN:	Origin of the chunk to be written
	datap	IN:	Buffer for the chunk data to be written

	Purpose	Writes a data chunk to a chunked data set.
	Return value	Returns SUCCEED (or 0) if successful and FAIL (or -1) otherwise.
	Description	SDwritechunk writes the entire chunk of data stored in the buffer datap to the chunked data set identified by the parameter sds_id. Writing starts at the location specified by the parameter origin. SDwritechunk is used when an entire chunk of data is to be written. SDwritedata is used when the write operation is to be done regardless of the chunking scheme used in the data set.
		SDwritechunk will return FAIL (or -1) when an attempt is made to use it to write to a non-chunked data set.
		The parameter origin specifies the coordinates of the chunk according to the chunk position in the overall chunk array. Refer to Chapter 3 of the HDF User's Guide, titled Scientific Data Sets (SD API), for a description of the organization of chunks in a data set.
		Note that there are two FORTRAN-77 versions of this routine; one for numeric data (sfwchnk) and one for character data (sfwcchnk).

	FORTRAN	integer sfwchnk(sds_id, origin, datap)
		integer sds_id, origin
		<valid numeric data type> datap(*)
		integer sfwcchnk(sds_id, origin, datap)
		integer sds_id, origin
		character*(*) datap(*)