!
!   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 
  INTEGER(hsize_t), DIMENSION(1:1) :: dims = (/15/) ! size of the VIIRS-MOD_GTM-EDR-GEO_Gran_0 dataset 
  TYPE(hdset_reg_ref_t_f), DIMENSION(1:15) :: ref ! array to READ region references 
  INTEGER(hsize_t), DIMENSION(1:4) :: buf  ! buffer to READ hyperslab coordinates defining region references 
  INTEGER :: status
  INTEGER(size_t) :: name_length
  CHARACTER(LEN = 50) :: name
  INTEGER(hid_t) :: dtype
  INTEGER(size_t) :: numelem
  INTEGER(size_t), PARAMETER :: type_string_length = 15
  CHARACTER(LEN=15) :: type_string
  INTEGER(hsize_t), DIMENSION(1:2) :: rdims
  REAL, ALLOCATABLE, DIMENSION(:), TARGET :: rdata
  INTEGER(size_t) :: rnumelem
  INTEGER :: class
  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 region reference information such as a name of the dataset the region reference point to,
  ! number of contiguous blocks in the selection (should be 1) and the hyperslab coordinates (0,0) - (770,4120)
  !
  
  ! Important to initialize optional variables
  name_length = LEN(name)
  dtype = 0
  name = ''

  CALL H5LRget_region_info_f(file_id, ref(3), status, LENGTH=name_length, PATH=name, DTYPE=dtype, &
       NUMELEM=numelem, BUF=buf)
  !
  ! Display the info
  !
  CALL H5Tget_class_f(dtype, class, status)
  WRITE(*, '(" Information retrieved by H5LRget_region_info:")')
  WRITE(*,'(" Third element of the array with the region references points to ",A)') name
  WRITE(*,'(" Length of the string above is ", I0)') name_length
  IF(class.EQ.H5T_FLOAT_F) WRITE(*,' (" Datatype of region is ", A)') "H5T_FLOAT_F"
  WRITE(*,'(" Number of blocks in the region is ", I0)') numelem
  WRITE(*,'(" Block''s coordinates are (",I0,",",I0,") - (",I0,",",I0,")",/)') buf(1),buf(2),buf(3),buf(4)

  !
  ! We will read data to the floating-point buffer using information provided by H5LRget_region_info
  ! to allocate the buffer to read data in.
     
  rdims(1) = buf(3) - buf(1) + 1
  rdims(2) = buf(4) - buf(2) + 1
  ALLOCATE(rdata(rdims(1) * rdims(2)))
  !
  ! Read data pointed by the third region reference into a buffer and display the first six elements.
  !
  f_ptr = C_LOC(rdata(1))
  CALL H5LRread_region_f(file_id, ref(3), H5T_NATIVE_REAL, rnumelem, f_ptr, status)

  WRITE(*,'(" Information retrieved by H5LRread_region:")')
  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)
  !
  ! Close dataset with region references and file.
  !
  CALL H5Dclose_f(dset_id, status)
  CALL H5Fclose_f(file_id, status)
  
END PROGRAM main