NCL Website header
NCL Home > Documentation > Functions > Interpolation, Ngmath routines

nngetslopes

Retrieves a slope at a specified coordinate position.

Prototype

	function nngetslopes (
		i [1] : integer,  
		j [1] : integer   
	)

	return_val [1] :  float

Arguments

i

A subscript indexing the first dimensioned variable in the output grid of the most recent call to natgrids.

j

A subscript indexing the second dimensioned variable in the output grid of the most recent call to natgrids.

Return value

The slope (a scalar value) at the specified coordinate position (if slopes were computed during the last call to natgrids).

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.)

nngetslopes is used to retrieve values which may have been computed during the last call to natgrids. Note that these values will only have been computed if you set the value of the control parameter "sdi" appropriately.

See Also

nngetslope

Examples

begin
;
; Define constants
;
  RAD2DEG = 57.29578
  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)

  u = new((/NUMXOUT,NUMYOUT/),float)
  v = new((/NUMXOUT,NUMYOUT/),float)

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

  yc = 1./(NUMYOUT-1.) 
  yo = ispan(0,NUMXOUT-1,1) * yc
;
;  Turn on gradient estimate calculations, flag calculation of
;  aspects and slopes, set flag to return aspects and slopes in
;  radians.
;
  nnsetp("SDI - compute slopes and aspects",1)
  nnsetp("IGR - use gradient estimates",1)
  nnsetp("RAD - return results in radians",1)
;
;  Do the interpolation.
;
  out = natgrids(x, y, z, xo, yo)
;
;  Get the aspects.
;
  do i=0,NUMXOUT-1
    do j=0,NUMYOUT-1
       rtmp = nngetaspects(i,j)
       u(i,j) = sin(rtmp)
       v(i,j) = cos(rtmp)
    end do
  end do

;
;  Get the slopes.
;
  do i = 0,NUMXOUT-1
    do j = 0,NUMYOUT-1
      rtmp = nngetslopes(i, j);
      u(i,j) = RAD2DEG*rtmp
    end do
  end do
end