!
!   This example opens an NPP example file and reads a dataset with region references 
!   VIIRS-MOD_GTM-EDR-GEO_Gran_0 under the /Data_Products/VIIRS-MOD-GTM-EDR-GEO group. 
!   Then it finds information about the selected elements pointed by the third reference 
!   and reads the data in.  
!   Main illustrative functions: H5LRget_region_info_f, H5LRread_region_f

PROGRAM main
  
  USE ISO_C_BINDING
  USE HDF5 ! module of HDF5 library
  USE H5LT ! module of H5LT
  USE H5HL_REGION

  IMPLICIT NONE

  CHARACTER(LEN=78), PARAMETER :: filename = &
       "GMGTO_npp_d20030125_t0657104_e0659047_b00014_c20090811150425926728_unkn_SCI.h5"

  CHARACTER(LEN=65), PARAMETER :: dsetname = &
       "/Data_Products/VIIRS-MOD-GTM-EDR-GEO/VIIRS-MOD-GTM-EDR-GEO_Gran_0" !dataset with region references

  INTEGER(hid_t) :: file_id ! file identifier
  INTEGER(hid_t) :: dset_id ! region reference dataset identifier
  TYPE(hdset_reg_ref_t_f), DIMENSION(1:15), TARGET :: ref ! array to read region references
  INTEGER :: status
  INTEGER(hid_t) :: dtype ! file datatype handle 
  INTEGER(hid_t) :: mtype ! mempry datatype handle
  INTEGER(size_t) :: msize ! size of memory datatype
  INTEGER(size_t) :: rnumelem ! number of elements to read
  REAL, ALLOCATABLE, DIMENSION(:), TARGET :: rdata ! POINTER to READ buffer
  INTEGER :: class
  INTEGER(HSIZE_T), DIMENSION(1:1) :: dims =(/15/)
  TYPE(C_PTR) :: f_ptr
  !
  !  Initialize FORTRAN interface.
  !
  CALL h5open_f(status)
  !
  ! Open the NPP file.
  ! 
  CALL H5Fopen_f(filename, H5F_ACC_RDWR_F, file_id, status)
  !
  ! Open dataset and read the dataset with the region references.
  ! We made an assumption that the size of the dataset is known.
  !
  CALL H5Dopen_f(file_id, dsetname, dset_id, status)
  CALL h5Dread_f(dset_id, H5T_STD_REF_DSETREG, ref, dims, status)
  ! 
  ! Get datatype of the data the region reference points to.
  !
  ! Important to initialize optional variables
  dtype = 0

  CALL H5LRget_region_info_f(file_id, ref(3), status, DTYPE=dtype)
  !
  ! Find the corresponding type in memory and its size.
  !
  CALL H5Tget_native_type_f(dtype, H5T_DIR_ASCEND_F, mtype, status)

  CALL H5Tget_size_f(mtype, msize, status)
  !
  ! Find number of elements in the region to read.
  !
  f_ptr = C_NULL_PTR
  CALL H5LRread_region_f(file_id, ref(3), mtype, rnumelem, f_ptr, status)

  CALL H5Tget_class_f(dtype, class, status)

  IF(class.EQ.H5T_FLOAT_F)THEN
     !
     ! Allocate buffer to read data in.
     !
     ALLOCATE( rdata(1:rnumelem) )

     f_ptr = C_LOC(rdata(1))
     CALL H5LRread_region_f(file_id, ref(3), mtype, rnumelem, f_ptr, status)

     WRITE(*,'(" Number of elements pointed by a region reference is ",I0)') rnumelem
     WRITE(*,'(" The first six elements are: ")')
     WRITE(*,'(6(x,f7.3))')  rdata(1:6)

     DEALLOCATE(rdata)
  ENDIF
  !
  ! Close dataset with region references and file.
  !
  CALL H5Dclose_f(dset_id,status)
  CALL H5Fclose_f(file_id,status)
  
END PROGRAM main