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nnpntinits

Initializes internal quantities, for given input data, to allow subsequent nnpnts calls to interpolate at specified points.

Prototype

```	procedure nnpntinits (
x [*] : float,
y [*] : float,
z [*] : float
)
```

Arguments

x

An array of X coordinates of the input data points (any length)

y

An array of Y coordinates of the input data points (same length as x)

z

An array of functional values at the input data points (same length as x)

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.)

nnpntinits initializes an interpolation process; it calculates and saves all natural neighbor relationships for a given set of input data (in which no missing values are allowed) and sets some control parameters so that nnpnt, nnpnts, or nnpntd can be called to interpolate at a specified set of points.

The values calculated by nnpntinits are stored in memory that it allocates. To release this memory, you must eventually call the procedure nnpntend or nnpntendd.

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|:)

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