The HDF_SD_SELECT function returns an SD dataset ID given the current SD interface ID, and the zero-based SD dataset index.
HDF_SD_FILEINFO can be used to determine the number of SD datasets in an HDF file, HDF_SD_REFTOINDEX can be used to find the index from its SD dataset ID, and HDF_SD_NAMETOINDEX can be used to find the index from its name.
sd_id = HDF_SD_START('test.hdf') ; Open an HDF file.
sds_id_1=HDF_SD_SELECT(sd_id, 0) ; Access the first SD in the HDF file.
HDF_SD_CREATE , HDF_SD_END , HDF_SD_ENDACCESS , HDF_SD_NAMETOINDEX , HDF_SD_REFTOINDEX , HDF_SD_SELECT , HDF_SD_START