NCL Website header
NCL Home > Documentation > Functions > WRF, File IO

wrf_wps_rdhead_int

Reads header information for the current field of an open WPS intermediate file.

Available in version 6.3.0 and later.

Prototype

	procedure wrf_wps_rdhead_int (
		istatus     [1] : integer,  
		rhead      [14] : float,    
		field       [1] : string,   
		date        [1] : string,   
		units       [1] : string,   
		map_source  [1] : string,   
		description [1] : string    
	)

Arguments

istatus

A scalar integer containing the status of the WPS filename that is open. This variable will get updated every time this procedure is called.

If istatus=0, then there is potentially more data to be read from the file.

If istatus=1 then either the header information couldn't be read, and/or there is no more data to be read from the file.

rhead

A preallocated float array of length 14 that will contain header values for each field. See the description below for more details.

field

A scalar string that will contain the field name of the current field.

date

A scalar string that will contain the date of the current field.

units

A scalar string that will contain the units of the current field.

map_source

A scalar string that will contain the map source of the current field.

description

A scalar string that will contain the description of the current field.

Description

This procedure reads information and header data for the current field of an open WPS intermediate file.

This procedure is meant to be used as part of a 3-step process for reading data off a WPS intermediate file:

  1. wrf_wps_open_int - open a WPS file
  2. wrf_wps_rdhead_int - read header info for current field
  3. wrf_wps_rddata_int - read data for current field

Steps #2 and #3 are meant to be called continuously in an NCL "do while" loop. The istatus variable will be set to 0 by this procedure to indicate the header was read successfully, and that you can now read the data for this field using wrf_wps_rddata_int. If istatus is not equal to 0, then no more data can be read, and the header information may potentially be incomplete.

Each argument to this procedure must be a variable that is preallocated using new. See the example below.

The rhead array will contain different header information, depending on the map projection of the current field. The map projection value is stored in rhead(0). Here's a full description of the contents of rhead:

For all fields:
version rhead(0)
forecast hour rhead(1)
level rhead(2)
nx rhead(3)
ny rhead(4)
projection
(0, 1, 3, 4, or 5)
rhead(5)
If projection = 0:
startlat rhead(6)
startlon rhead(7)
deltalat rhead(8)
deltalon rhead(9)
earth_radius rhead(10)
If projection = 1:
startlat rhead(6)
startlon rhead(7)
dx rhead(8)
dy rhead(9)
truelat1 rhead(10)
earth_radius rhead(11)
If projection = 3:
startlat rhead(6)
startlon rhead(7)
dx rhead(8)
dy rhead(9)
center_lon rhead(10)
truelat1 rhead(11)
truelat2 rhead(12)
earth_radius rhead(13)
If projection = 4:
startlat rhead(6)
startlon rhead(7)
nlats rhead(8)
deltalon rhead(9)
earth_radius rhead(10)
If projection = 5:
startlat rhead(6)
startlon rhead(7)
dx rhead(8)
dy rhead(9)
center_lon rhead(10)
truelat1 rhead(11)
earth_radius rhead(12)

To read a WPS file with a single function call, see wrf_wps_read_int. The examples below illustrate both methods for reading a WPS file.

See Also

wrf_wps_open_int, wrf_wps_rdhead_int, wrf_wps_rddata_int, wrf_wps_read_int, wrf_wps_write_int, wrf_wps_close_int

Examples

Example 1

This example shows how to use the three-step process of reading a WPS intermediate file using 1) wrf_wps_open_int, 2) wrf_wps_rdhead_int, and 3) wrf_wps_rddata_int.

See example 2 below for a script that uses wrf_wps_read_int to read the file in one step.

  wps_filename = "NNRP:2006-04-10_00"

;---Preallocate variables for header
  header      = new(14,float)
  field       = new(1,string)
  date        = new(1,string)
  units       = new(1,string)
  map_source  = new(1,string)
  description = new(1,string)
  
  istatus =  wrf_wps_open_int(wps_filename)
  if(istatus.ne.0) then
    print("Error opening " + wps_filename)
    exit
  end if

;---Continuously read data from WPS file until istatus != 0.
  nfields = 0

  do while (istatus.eq.0)

;---Read header
    wrf_wps_rdhead_int(istatus,header,field,date,units,\
                       map_source,description)
    if(istatus.ne.0) then
      continue
    end if

    nx = toint(header(3))
    ny = toint(header(4))

;---Read data
    slab := wrf_wps_rddata_int(istatus,nx,ny)
    if(istatus.ne.0) then
      continue
    end if

;---Print information about each slab
    print("Field #" + (nfields+1))
    print("  name          : '" + field + "'")
    print("  description   : '" + description + "'")
    print("  units         : '" + units + "'")
    print("  min/max value : "  + min(slab) + " / " + max(slab))
    print("  date          : '" + date + "'")
    print("  map source    : '" + map_source + "'")
    print("  version       : " + header(0))
    print("  forecast hour : " + header(1))
    print("  level         : " + header(2))
    print("  ny x nx       : " + header(4) + " x " + header(3))
    print("  projection    : " + header(5))
    if(header(5).eq.0) then
      print("  startlat      : " + header(6))
      print("  startlon      : " + header(7))
      print("  deltalat      : " + header(8))
      print("  deltalon      : " + header(9))
      print("  earth_radius  : " + header(10))
    else if(header(5).eq.1) then
      print("  startlat      : " + header(6))
      print("  startlon      : " + header(7))
      print("  dy x dx       : " + header(9) + " x " + header(8))
      print("  truelat1      : " + header(10))
      print("  earth_radius  : " + header(11))
    else if(header(5).eq.3) then
      print("  startlat      : " + header(6))
      print("  startlon      : " + header(7))
      print("  dy x dx       : " + header(9) + " x " + header(8))
      print("  center lon    : " + header(10))
      print("  truelat1      : " + header(11))
      print("  truelat2      : " + header(12))
      print("  earth_radius  : " + header(13))
    else if(header(5).eq.4) then
      print("  startlat      : " + header(6))
      print("  startlon      : " + header(7))
      print("  nlats         : " + header(8))
      print("  deltalon      : " + header(9))
      print("  earth_radius  : " + header(10))
    else if(header(5).eq.5) then
      print("  startlat      : " + header(6))
      print("  startlon      : " + header(7))
      print("  dy x dx       : " + header(9) + " x " + header(8))
      print("  center lon    : " + header(10))
      print("  truelat1      : " + header(11))
      print("  earth_radius  : " + header(12))
    end if
    end if
    end if
    end if
    end if
    nfields = nfields + 1
  end do

  print("There were " + nfields + " fields in the " + wps_filename + " WPS file.")

Output: (run with "-n" option to remove annoying "(0)")

Field #1
  name          : 'PMSL'
  description   : 'Sea-level Pressure'
  units         : 'Pa'
  min/max value : 95120 / 107780
  date          : '2006-04-10_00:00:00'
  map source    : 'unknown model from NCEP GRID   2'
  version       : 5
  forecast hour : 0
  level         : 201300
  ny x nx       : 73 x 144
  projection    : 0
  startlat      : 90
  startlon      : 0
  deltalat      : -2.5
  deltalon      : 2.5
  earth_radius  : 6371.23
  .
  .
  .
Field #100
  name          : 'HGT'
  description   : 'Height'
  units         : 'm'
  min/max value : 29479 / 31173
  date          : '2006-04-10_00:00:00'
  map source    : 'unknown model from NCEP GRID   2'
  version       : 5
  forecast hour : 0
  level         : 1000
  ny x nx       : 73 x 144
  projection    : 0
  startlat      : 90
  startlon      : 0
  deltalat      : -2.5
  deltalon      : 2.5
  earth_radius  : 6371.23
There were 100 fields in the NNRP:2006-04-10_00 WPS file.

Example 2

This example shows how to use wrf_wps_read_int to read a WPS intermediate file in one step.

  wps_filename = "NNRP:2006-04-10_00"

  slabs = wrf_wps_read_int(wps_filename)

  slabs_dims = dimsizes(slabs)
  header     = slabs@rhead          ; Read into memory so we can subscript it
  nfields    = slabs_dims(0)

  print("There are " + nfields + " fields in the " + wps_filename + " WPS file.")

  do nf=0,nfields-1
;---Print information about each slab
    print("Field #" + (nf+1))
    print("  name          : '" + slabs@field(nf) + "'")
    print("  description   : '" + slabs@description(nf) + "'")
    print("  units         : '" + slabs@units(nf) + "'")
    print("  min/max value : "  + min(slabs(nf,:,:)) + " / " + max(slabs(nf,:,:)))
    print("  date          : '" + slabs@hdate(nf) + "'")
    print("  map source    : '" + slabs@map_source(nf) + "'")
    print("  version       : " + header(nf,0))
    print("  forecast hour : " + header(nf,1))
    print("  level         : " + header(nf,2))
    print("  ny x nx       : " + header(nf,4) + " x " + header(nf,3))
    print("  projection    : " + header(nf,5))
    if(header(nf,5).eq.0) then
      print("startlat        : " + header(nf,6))
      print("  startlon      : " + header(nf,7))
      print("  deltalat      : " + header(nf,8))
      print("  deltalon      : " + header(nf,9))
      print("  earth_radius  : " + header(nf,10))
    else if(header(nf,5).eq.1) then
      print("  startlat      : " + header(nf,6))
      print("  startlon      : " + header(nf,7))
      print("  dy x dx       : " + header(nf,9) + " x " + header(nf,8))
      print("  truelat1      : " + header(nf,10))
      print("  earth_radius  : " + header(nf,11))
    else if(header(nf,5).eq.3) then
      print("  startlat      : " + header(nf,6))
      print("  startlon      : " + header(nf,7))
      print("  dy x dx       : " + header(nf,9) + " x " + header(nf,8))
      print("  center lon    : " + header(nf,10))
      print("  truelat1      : " + header(nf,11))
      print("  truelat2      : " + header(nf,12))
      print("  earth_radius  : " + header(nf,13))
    else if(header(nf,5).eq.4) then
      print("  startlat      : " + header(nf,6))
      print("  startlon      : " + header(nf,7))
      print("  nlats         : " + header(nf,8))
      print("  deltalon      : " + header(nf,9))
      print("  earth_radius  : " + header(nf,10))
    else if(header(nf,5).eq.5) then
      print("  startlat      : " + header(nf,6))
      print("  startlon      : " + header(nf,7))
      print("  dy x dx       : " + header(nf,9) + " x " + header(nf,8))
      print("  center lon    : " + header(nf,10))
      print("  truelat1      : " + header(nf,11))
      print("  earth_radius  : " + header(nf,12))
    end if
    end if
    end if
    end if
    end if
  end do

Output: (run with "-n" option to remove annoying "(0)")

There are 100 fields in the NNRP:2006-04-10_00 WPS file.

Field #1
  name          : 'PMSL'
  description   : 'Sea-level Pressure'
  units         : 'Pa'
  min/max value : 0 / 107780
  date          : '2006-04-10_00:00:00'
  map source    : 'unknown model from NCEP GRID   2'
  version       : 5
  forecast hour : 0
  level         : 201300
  ny x nx       : 73 x 144
  projection    : 0
  startlat      : 90
  startlon      : 0
  deltalat      : -2.5
  deltalon      : 2.5
  earth_radius  : 6371.23
  .
  .
  .
Field #100
  name          : 'HGT'
  description   : 'Height'
  units         : 'm'
  min/max value : 0 / 31173
  date          : '2006-04-10_00:00:00'
  map source    : 'unknown model from NCEP GRID   2'
  version       : 5
  forecast hour : 0
  level         : 1000
  ny x nx       : 73 x 144
  projection    : 0
  startlat      : 90
  startlon      : 0
  deltalat      : -2.5
  deltalon      : 2.5
  earth_radius  : 6371.23