NCL Home > Documentation > Functions > Regridding

triple2grid2d

Places randomly-spaced data onto the nearest locations of a grid described by two-dimensional coordinate arrays.

Prototype

	function triple2grid2d (
		x        [*] : numeric,  
		y        [*] : numeric,  
		data     [*] : numeric,  
		xgrid [*][*] : numeric,  
		ygrid [*][*] : numeric,  
		option   [1] : logical   
	)

	return_val [dimsizes(xgrid)] :  typeof(data)

Arguments

x
y

One-dimensional arrays containing the coordinates associated with the data values. For geophysical variables, x and y correspond to longitude and latitude respectively.

data

A one-dimensional array containing the values associated with the x and y coordinates. Missing values may be present (data@_FillValue), but they are ignored.

xgrid

A two-dimensional array containing the X coordinates to be associated with the returned two-dimensional grid. For geophysical variables, these are longitudes.

ygrid

A two-dimensional array of the same size as xgrid containing the Y coordinates to be associated with the returned two-dimensional grid. For geophysical variables, these are latitudes.

option

If option=False, the function will operate under default mode (that is, all grid points will be assigned a value).

If option=True, then this variable may have associated with it the attributes mopt and/or distmx.

option@mopt - an integer value of 0 or 1

option@mopt=0 (default) - use a quick approximation to determine the distance of an x/y location to a grid point.

option@mopt=1 - calculate the distance using the great circle distance formula. This will result in slower execution times.

option@distmx

Any x/y/data observation greater than option@distmx from a grid point will not be used. Note: If this option is used, it is possible for some grid points to be returned as missing (data@_FillValue).

Return value

The returned two-dimensional array will be the same size as the xgrid/ygrid arrays and the same type as data.

Description

This routine does not perform interpolation; rather, each individual data point is assigned to the nearest grid point. It is possible that upon return, grid will contain grid points set to data@_FillValue if the option@distmx is set.

The units of distmx are "grid-units" if the default distance formula is used, and kilometers if the great circle distance formula is used, as indicated by option@mopt.

Examples

Example 1

Assume xlon, ylat, and zVal are one-dimensional (1D) arrays of length KPTS. Assume lon and lat are 2D arrays specifying grid locations. Then:

   grid = triple2grid2d(xlon,ylat,zVal, lon,lat, False)

will use default behavior and return a 2D array of the same size as xgrid.

Setting option=True and option@mopt=1 will result in the function using the more accurate great circle distance formula. The execution time will be longer, however:

  opt       = True       ; setting options
  opt@mopt  = 1    
  grid      = triple2grid2d(xlon,ylat,zVal, lon,lat, opt)

Setting the option@distmx option will result in any observation greater than distmx to be not used: