
wrf_ll_to_ij
Finds the nearest model grid indices (i,j) to the specified location(s) in longitude and latitude (deprecated).
Prototype
function wrf_ll_to_ij ( lon : numeric, lat : numeric, opt : logical ) return_val : float or double
Arguments
lonlat
Longitude and latitude arrays in ARW WRF.
optA logical scalar containing attributes. See description below.
Description
This function was deprecated in NCL version 6.6.0. Use wrf_user_ll_to_xy instead.
The return value is a multi-dimensional float or double array that holds the closest I, J positions to the input lon, lat values. The dimensions will be 2 x N:
- N represents the dimensions of lon and lat
- loc(0,:,...,:) --> I values
loc(1,:,...,:) --> J values
The opt variable can contain the following attributes, many of which are included as global attributes on the WRF output file. Attributes are case-insensitive:
- MAP_PROJ - Model projection [1=Lambert, 2=polar
stereographic, 3=mercator, 6=lat-lon] (required)
- TRUELAT1 - required for MAP_PROJ = 1, 2, 3
(defaults to 0 otherwise)
- TRUELAT2 - required for MAP_PROJ = 6 (defaults
to 0 otherwise)
- STAND_LON - Standard longitude used in model projection
(required)
- REF_LON, REF_LON - A reference longitude and latitude
(required)
- KNOWNI, KNOWNJ - The I and J locations of REF_LON
and REF_LAT (required)
- POLE_LAT - optional for MAP_PROJ = 6 (defaults
to 90 otherwise)
- POLE_LAT - optional for MAP_PROJ = 6 (defaults
to 0 otherwise)
- DX, DY - required for MAP_PROJ = 1, 2, 3
(defaults to 0 otherwise)
- LATINC, LONINC - required for MAP_PROJ = 6 (defaults to 0 otherwise)
See Also
wrf_user_ll_to_xy, wrf_user_xy_to_ll
Examples
Example 1
opt = True opt@MAP_PROJ = 1 opt@TRUELAT1 = 30.0 opt@TRUELAT2 = 60.0 opt@STAND_LON = -98.0 opt@REF_LAT = 34.83 opt@REF_LON = -81.03 opt@KNOWNJ = 37.0 opt@KNOWNI = 30.5 opt@DX = 30000. opt@DY = 30000. loc = wrf_ll_to_ij( -80.0, 30.0, opt )
Example 2
nc_file = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r") opt = True opt@MAP_PROJ = nc_file@MAP_PROJ opt@TRUELAT1 = nc_file@TRUELAT1 opt@TRUELAT2 = nc_file@TRUELAT2 opt@STAND_LON = nc_file@STAND_LON opt@DX = nc_file@DX opt@DY = nc_file@DY XLAT = nc_file->XLAT(0,:,:) XLONG = nc_file->XLONG(0,:,:) opt@REF_LAT = XLAT(0,0) opt@REF_LON = XLONG(0,0) opt@KNOWNI = 1.0 opt@KNOWNJ = 1.0 loc = wrf_ll_to_ij ( -80.0, 30.0, opt )
Example 3
The function wrf_user_ll_to_ij, (available in the $NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl script) can be used to locate i,j points given specific lon, lat references.
load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/gsn_code.ncl" load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl" a = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r") opt = True opt@returnInt = False ; Return real values (set to True for integer values - integer is default) loc = wrf_user_ll_to_ij (a, -80.0, 30.0, opt)
Example 4
You can see another specific example of using wrf_user_ll_to_ij to get temperature at a specific location: http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/Examples/SPECIAL/wrf_meteo_5.ncl
There are other example scripts and their resultant images at:
http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/