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2.3.3.2 pres_temp_4D_rd.f90
     ! This is part of the netCDF package.
     ! Copyright 2006 University Corporation for Atmospheric Research/Unidata.
     ! See COPYRIGHT file for conditions of use.
     
     ! This is an example which reads some 4D pressure and
     ! temperatures. The data file read by this program is produced by
     ! the companion program pres_temp_4D_wr.f90. It is intended to
     ! illustrate the use of the netCDF Fortran 90 API.
     
     ! This program is part of the netCDF tutorial:
     ! http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-tutorial
     
     ! Full documentation of the netCDF Fortran 90 API can be found at:
     ! http://www.unidata.ucar.edu/software/netcdf/docs/netcdf-f90
     
     ! $Id: pres_temp_4D_rd.f90,v 1.9 2010/04/06 19:32:09 ed Exp $
     
     program pres_temp_4D_rd
       use netcdf
       implicit none
     
       ! This is the name of the data file we will read.
       character (len = *), parameter :: FILE_NAME = "pres_temp_4D.nc"
       integer :: ncid
     
       ! We are reading 4D data, a 12 x 6 x 2 lon-lat-lvl grid, with 2
       ! timesteps of data.
       integer, parameter :: NDIMS = 4, NRECS = 2
       integer, parameter :: NLVLS = 2, NLATS = 6, NLONS = 12
       character (len = *), parameter :: LVL_NAME = "level"
       character (len = *), parameter :: LAT_NAME = "latitude"
       character (len = *), parameter :: LON_NAME = "longitude"
       character (len = *), parameter :: REC_NAME = "time"
     
       ! The start and count arrays will tell the netCDF library where to
       ! read our data.
       integer :: start(NDIMS), count(NDIMS)
     
       ! In addition to the latitude and longitude dimensions, we will also
       ! create latitude and longitude variables which will hold the actual
       ! latitudes and longitudes. Since they hold data about the
       ! coordinate system, the netCDF term for these is: "coordinate
       ! variables."
       real :: lats(NLATS), lons(NLONS)
       integer :: lon_varid, lat_varid
     
       ! We will read surface temperature and pressure fields. In netCDF
       ! terminology these are called "variables."
       character (len = *), parameter :: PRES_NAME="pressure"
       character (len = *), parameter :: TEMP_NAME="temperature"
       integer :: pres_varid, temp_varid
     
       ! We recommend that each variable carry a "units" attribute.
       character (len = *), parameter :: UNITS = "units"
       character (len = *), parameter :: PRES_UNITS = "hPa", TEMP_UNITS = "celsius"
       character (len = *), parameter :: LAT_UNITS = "degrees_north"
       character (len = *), parameter :: LON_UNITS = "degrees_east"
     
       ! Program variables to hold the data we will read in. We will only
       ! need enough space to hold one timestep of data; one record.
       ! Allocate memory for data.
       real, dimension(:,:,:), allocatable :: pres_in
       real, dimension(:,:,:), allocatable :: temp_in
       real, parameter :: SAMPLE_PRESSURE = 900.0
       real, parameter :: SAMPLE_TEMP = 9.0
     
       ! Use these to calculate the values we expect to find.
       real, parameter :: START_LAT = 25.0, START_LON = -125.0
     
       ! Loop indices
       integer :: lvl, lat, lon, rec, i
     
       ! Allocate memory.
       allocate(pres_in(NLONS, NLATS, NLVLS))
       allocate(temp_in(NLONS, NLATS, NLVLS))
     
       ! Open the file.
       call check( nf90_open(FILE_NAME, nf90_nowrite, ncid) )
     
       ! Get the varids of the latitude and longitude coordinate variables.
       call check( nf90_inq_varid(ncid, LAT_NAME, lat_varid) )
       call check( nf90_inq_varid(ncid, LON_NAME, lon_varid) )
     
       ! Read the latitude and longitude data.
       call check( nf90_get_var(ncid, lat_varid, lats) )
       call check( nf90_get_var(ncid, lon_varid, lons) )
     
       ! Check to make sure we got what we expected.
       do lat = 1, NLATS
          if (lats(lat) /= START_LAT + (lat - 1) * 5.0) stop 2
       end do
       do lon = 1, NLONS
          if (lons(lon) /= START_LON + (lon - 1) * 5.0) stop 2
       end do
     
       ! Get the varids of the pressure and temperature netCDF variables.
       call check( nf90_inq_varid(ncid, PRES_NAME, pres_varid) )
       call check( nf90_inq_varid(ncid, TEMP_NAME, temp_varid) )
     
       ! Read 1 record of NLONS*NLATS*NLVLS values, starting at the beginning
       ! of the record (the (1, 1, 1, rec) element in the netCDF file).
       count = (/ NLONS, NLATS, NLVLS, 1 /)
       start = (/ 1, 1, 1, 1 /)
     
       ! Read the surface pressure and temperature data from the file, one
       ! record at a time.
       do rec = 1, NRECS
          start(4) = rec
          call check( nf90_get_var(ncid, pres_varid, pres_in, start = start, &
                                   count = count) )
          call check( nf90_get_var(ncid, temp_varid, temp_in, start, count) )
     
          i = 0
          do lvl = 1, NLVLS
             do lat = 1, NLATS
                do lon = 1, NLONS
                   if (pres_in(lon, lat, lvl) /= SAMPLE_PRESSURE + i) stop 2
                   if (temp_in(lon, lat, lvl) /= SAMPLE_TEMP + i) stop 2
                   i = i + 1
                end do
             end do
          end do
          ! next record
       end do
     
       ! Close the file. This frees up any internal netCDF resources
       ! associated with the file.
       call check( nf90_close(ncid) )
     
       ! If we got this far, everything worked as expected. Yipee!
       print *,"*** SUCCESS reading example file ", FILE_NAME, "!"
     
     contains
       subroutine check(status)
         integer, intent ( in) :: status
     
         if(status /= nf90_noerr) then
           print *, trim(nf90_strerror(status))
           stop 2
         end if
       end subroutine check
     end program pres_temp_4D_rd