wrf_latlon_to_ij

Finds the nearest model grid indices (i,j) to the specific location(s) in latitude and longitude (deprecated).

Prototype

	function wrf_latlon_to_ij (
		lat_wrf     : numeric,  
		lon_wrf     : numeric,  
		lat_pts [*] : numeric,  
		lon_pts [*] : numeric   
	)

	return_val  :  integer

Arguments

Latitude and longitude arrays in ARW WRF, whose rightmost dimensions are ny x nx.

Scalars representing the lat/lon locations. (In version 4.3.1 the interface was upgraded to allow these variables to be 1D arrays.)

If any of the input values are out of data range in lat_wrf and/or lon_wrf, then the appropriate return values will be set to the default missing value for an integer (-999 for versions 5.2.x and earlier, -2147483647 for versions 6.x and later).

Description

This function was deprecated in NCL version 5.1.0. Use wrf_user_ll_to_xy instead.

This function returns the i-th, j-th grid location of the given location(s) (lat, lon). This is basically same as "get_ij_lat_long" in "wrf_user_fortran_util_0.f".

Note: in NCL V6.0.0, the default missing value was changed from the old value of -999 to the new default missing for an NCL integer (-2147483647).

Second note: this function was available in V4.3.0, but it was overhauled in V4.3.1 to do the correct thing with values outside the range of the input, so the 4.3.0 version should not be used.

See Also

wrf_user_ll_to_xy, wrf_user_xy_to_ll

See the full list of WRF functions.

Examples

The function wrf_user_latlon_to_ij, (available in the $NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl script) can be used to locate x/y point given specific long/lat references.

Example 1

  a=addfile("wrfout_d01_2000-01-24_12:00:00.nc","r")
  wlat=a->XLAT(0,:,:)
  wlon=a->XLONG(0,:,:)
  print(min(wlat)+","+max(wlat))  ; 7.97334,55.7424
  print(min(wlon)+","+max(wlon))  ; 98.3065,177.803

; A sample observation site
  olat=36.5
  olon=121.4

; Find the closest point to the site in WRF grids
  obsij=wrf_latlon_to_ij(wlat,wlon,olat,olon)
;  obsij=wrf_user_ll_to_xy(wlat,wlon,olat,olon)
  print(obsij)    ; => 63,29

  b=addfile("wrfout_d01_2000-01-24_12:00:00.nc","r")
  wlat=b->XLAT(0,:,:)
  wlon=b->XLONG(0,:,:)

  c=addfile("Wprf.nc","r")        ; Wind profiler observations
  locs=tostring(c->id)   ; station names
  nloc=dimsizes(locs)             ; 36 stations
  lats=c->lat                     ; float [station | 36]
  lons=c->lon                     ; float [station | 36]

;
; The following will only work in version 4.3.1.
;
  loc_ij =wrf_latlon_to_ij(wlat,wlon,lats,lons)   ; 36 x 2
  print(locs+":"+loc_ij(:,0)+","+loc_ij(:,1))

  load "$NCARG_ROOT/lib/ncarg/nclscripts/gsn/gsn_code.ncl"
  load "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUserARW.ncl"

  a = addfile("wrfout_d01_2000-01-24_12:00:00.nc","r")

  loc  = wrf_user_latlon_to_ij(a, 40.0, -100.0)
  print("X/Y location is: " +loc)