nnpnt

Interpolates from 2D random data to get values at a specified set of points.

Prototype

	function nnpnt (
		x [*] : numeric,  
		y [*] : numeric   
	)

	return_val [dimsizes(x)] :  float or double

Arguments

An array of X coordinates of points where interpolation is desired, of length npts.

An array of Y coordinates of points where interpolation is desired, of length npts.

Return value

An array, of the same size as x and y, containing interpolated function values.

The output array will be of type double if any of the input is double, and float otherwise.

Description

This function is part of the Natgrid package, which implements a natural neighbor interpolation method. Much useful information is available at the above link, including the descriptions of many control parameters that can be modified to materially change its behavior. (The functions nngetp and nnsetp are used to access these parameters.)

nnpnt interpolates to get function values at specified points. It may only be called after calling nnpntinit, nnpntinits, or nnpntinitd.

nnpntinit and nnpnt are "generic" functions that accept any type of numeric input, nnpntinits and nnpnts require input of type float, and nnpntinitd and nnpntd require input of type double. However, each of these references the same internal structure, so it is possible to use one form for the initialization and another form for the actual interpolation.

Examples

begin
  NUMXOUT = 21
  NUMYOUT = 21
;
;  Coordinate data are defined as random numbers between -0.2
;  and 1.2 and are explicitly defined here for uniformity
;  across platforms.
; 
  x = (/                                                        \
  1.16,  0.47,  0.29,  0.72,  0.52,  1.12,  0.33,  0.20,  0.30, \
  0.78,  0.92,  0.52,  0.44,  0.22, -0.10,  0.11,  0.59,  1.13, \
  0.68,  1.11,  0.93,  0.29,  0.74,  0.43,  0.87,  0.87, -0.10, \
  0.26,  0.85,  0.00, -0.02,  1.01, -0.12,  0.65,  0.39,  0.96, \
  0.39,  0.38,  0.94, -0.03, -0.17,  0.00,  0.03,  0.67, -0.06, \
  0.82, -0.03,  1.08,  0.37,  1.02, -0.11, -0.13,  1.03,  0.61, \
  0.26,  0.18,  0.62,  0.42,  1.03,  0.72,  0.97,  0.08,  1.18, \
  0.00,  0.69,  0.10,  0.80,  0.06,  0.82,  0.20,  0.46,  0.37, \
  1.16,  0.93,  1.09,  0.96,  1.00,  0.80,  0.01,  0.12,  1.01, \
  0.48,  0.79,  0.04,  0.42,  0.48, -0.18,  1.16,  0.85,  0.97, \
  0.14,  0.40,  0.78,  1.12,  1.19,  0.68,  0.65,  0.41,  0.90, \
  0.84, -0.11, -0.01, -0.02, -0.10,  1.04,  0.58,  0.61,  0.12, \
 -0.02, -0.03,  0.27,  1.17,  1.02,  0.16, -0.17,  1.03,  0.13, \
  0.04, -0.03,  0.15,  0.00, -0.01,  0.91,  1.20,  0.54, -0.14, \
  1.03,  0.93,  0.42,  0.36, -0.10,  0.57,  0.22,  0.74,  1.15, \
  0.40,  0.82,  0.96,  1.09,  0.42,  1.13,  0.24,  0.51,  0.60, \
  0.06,  0.38,  0.15,  0.59,  0.76,  1.16,  0.02,  0.86,  1.14, \
  0.37,  0.38,  0.26,  0.26,  0.07,  0.87,  0.90,  0.83,  0.09, \
  0.03,  0.56, -0.19,  0.51,  1.07, -0.13,  0.99,  0.84,  0.22 /)

  y = (/                                                        \
 -0.11,  1.07,  1.11, -0.17,  0.08,  0.09,  0.91,  0.17, -0.02, \
  0.83,  1.08,  0.87,  0.46,  0.66,  0.50, -0.14,  0.78,  1.08, \
  0.65,  0.00,  1.03,  0.06,  0.69, -0.16,  0.02,  0.59,  0.19, \
  0.54,  0.68,  0.95,  0.30,  0.77,  0.94,  0.76,  0.56,  0.12, \
  0.05, -0.07,  1.01,  0.61,  1.04, -0.07,  0.46,  1.07,  0.87, \
  0.11,  0.63,  0.06,  0.53,  0.95,  0.78,  0.48,  0.45,  0.77, \
  0.78,  0.29,  0.38,  0.85, -0.10,  1.17,  0.35,  1.14, -0.04, \
  0.34, -0.18,  0.78,  0.17,  0.63,  0.88, -0.12,  0.58, -0.12, \
  1.00,  0.99,  0.45,  0.86, -0.15,  0.97,  0.99,  0.90,  0.42, \
  0.61,  0.74,  0.41,  0.44,  1.08,  1.06,  1.18,  0.89,  0.74, \
  0.74, -0.06,  0.00,  0.99,  0.03,  1.00, -0.04,  0.24,  0.65, \
  0.12,  0.13, -0.09, -0.05,  1.03,  1.07, -0.02,  1.18,  0.19, \
  0.03, -0.03,  0.86,  1.12,  0.38,  0.72, -0.20, -0.08, -0.18, \
  0.32,  0.13, -0.19,  0.93,  0.81,  0.31,  1.09, -0.03,  1.01, \
 -0.17,  0.84, -0.11,  0.45,  0.18,  0.23,  0.81,  0.39,  1.09, \
 -0.05,  0.58,  0.53,  0.96,  0.43,  0.48,  0.96, -0.03,  1.13, \
  1.16,  0.16,  1.15,  0.57,  0.13,  0.71,  0.35,  1.04,  0.62, \
  1.03,  0.98,  0.31,  0.70,  0.97,  0.87,  1.14,  0.08,  1.19, \
  0.88,  1.00,  0.51,  0.03,  0.17,  1.01,  0.44,  0.17, -0.11 /)

  z = (x-0.25)*(x-0.25) + (y-0.50)*(y-0.50)

  xc = 1./(NUMXOUT-1.)
  xo = ispan(0,NUMXOUT-1,1) * xc

  yc = 1./(NUMYOUT-1.)
  yo = ispan(0,NUMYOUT-1,1) * yc

;
; 2D representations of xo and yo.
;
  xo2d_1   = onedtond(xo,(/NUMYOUT,NUMXOUT/))
  yo2d     = onedtond(yo,(/NUMXOUT,NUMYOUT/))
  xo2d_1!0 = "y"
  xo2d_1!1 = "x"
  xo2d     = xo2d_1(x|:,y|:)

  nnpntinit(x,y,z)
  zo1d = nnpnt(ndtooned(xo2d),ndtooned(yo2d))    ; Interpolate.
  zo2d = onedtond(zo1d,(/NUMXOUT,NUMYOUT/))      ; Convert to 2D.
  nnpntend()                                     ; Clean up.
end