NCL Home > Documentation > Functions > Array query, Lat/Lon functions

region_ind

Returns the indices (subscripts) of two-dimensional latitude/longitude arrays that span user specified latitude/longitude boundaries.

Available in version 5.1.0 or later.

Prototype

load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"

	function region_ind (
		lat2d [*][*] : numeric,  
		lon2d [*][*] : numeric,  
		latS     [1] : numeric,  
		latN     [1] : numeric,  
		lonW     [1] : numeric,  
		lonE     [1] : numeric   
	)

	return_val  :  (4)  [integer]

Arguments

lat2d

A two-dimensional array that contains latitudes.

lon2d

A two-dimensional array that contains longitudes.

latS

Southern boundary

latS

Northern boundary

lonW

Western boundary

lonE

Eastern boundary

Return value

A one dimensional array of length 4 containing integer subscripts which span the region of interest.

Description

Finds the first and last indices (subscripts) of two-dimensional lat2d/lon2d arrays containing the region of interest.

Note: This function may not be appropriate for all curvilinear grids.

Examples

Example 1

Find the indices (subscripts) which span a user specified region of interest.

  load "$NCARG_ROOT/lib/ncarg/nclscripts/csm/contributed.ncl"
       ;
       ;
  f     = addfile("NARRmonhr-b_221_20021201_2100_000.grb" , "r")

  glon2d =  f->gridlon_221
  glat2d =  f->gridlat_221

  printMinMax(glat2d, True)
  printMinMax(glon2d, True)

  latS   = 30                      ; California [*rough*]
  latN   = 43
  lonL   = -125
  lonR   = -113

  ji = region_ind (glat2d,glon2d, latS, latN, lonW, lonE)

   iStrt = ji(0)      ; lat start
   jLast = ji(1)      ; lat last
   iStrt = ji(2)      ; lon start
   iLast = ji(3)      ; lon last

   LAT2D = glat2d(jStrt:jLast,iStrt:iLast)
   LON2D = glon2d(jStrt:jLast,iStrt:iLast)

  printMinMax(LAT2D, True)
  printMinMax(LON2D, True)

                      ; read data just for the region of interest
   x     = f->LHTFL_221_SFC_113(:,jStrt:jLast,iStrt:iLast)

The (edited) output

(0)	glat2d: min=   0.898   max= 85.334 
(0)	glon2d: min=-179.998   max=179.992

(0)	LAT2D : min=  28.680   max=  44.247 
(0)	LON2D : min=-128.941   max=-111.976