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# dsgrid3

Interpolates data from an unstructured (randomly-spaced) grid to a 3D grid using inverse distance weighted interpolation.

## Prototype

```	function dsgrid3 (
x  [*] : numeric,
y  [*] : numeric,
z  [*] : numeric,
u      : numeric,
xo [*] : numeric,
yo [*] : numeric,
zo [*] : numeric
)

return_val [dimsizes(x) * dimsizes(y) * dimsizes(z)] :  float or double
```

## Arguments

x

A 1D array of length npts containing the X coordinates of the input data.

For lat/lon data, x represents the longitude values.

y

A 1D array of length npts containing the Y coordinates of the input data.

For lat/lon data, y represents the latitude values.

z

A 1D array of length npts containing the Z coordinates of the input data.

u

An array of any dimensionality (last dimension must be npts) containing the functional values of the input data. Element u(...,i) is the value of the input function at coordinate (x(i), y(i), z(i)) for i = 0, npts - 1).

xo

A 1D array of any length (numxout) containing the X coordinates of the output data grid. The values in xo must be increasing, but need not be equally spaced.

yo

A 1D array of any length (numyout) containing the Y coordinates of the output data grid. The values in yo must be increasing, but need not be equally spaced.

zo

A 1D array of any length (numzout) containing the Z coordinates of the output data grid. The values in zo must be increasing, but need not be equally spaced.

## Return value

Returns a floating point array dimensioned as N x numxout x numyout x numzout, where N represents all but the last dimension of u. The return value type is double if u is of type double.

## Description

This function interpolates data from an unstructured (randomly-spaced) grid to a 3D grid.

This function requires that desired values for control parameters have been set using the procedure dssetp.

This function is part of the Dsgrid package which implements a simple inverse distance weighted interpolation algorithm. No missing values are allowed.

## Examples

```begin

NUM = 1000
NX  = 21
NY  = 21
NZ  = 21
RAND_MAX = 32767.0

xi = new((/NUM/), float)
yi = new((/NUM/), float)
zi = new((/NUM/), float)
u  = new((/NUM/), float)

xo = new((/NX/), float)
yo = new((/NY/), float)
zo = new((/NZ/), float)

xmin = -2.0
ymin = -2.0
zmin = -2.0
xmax =  2.0
ymax =  2.0
zmax =  2.0

;
; Create random data in three space and define a function.
;
rand1 = new((/NUM/), float)
rand2 = new((/NUM/), float)
rand3 = new((/NUM/), float)
srand(1)
do i = 0,NUM - 1
rand1(i) = rand
rand2(i) = rand
rand3(i) = rand
end do
xi = xmin + (xmax - xmin) * (rand1 / RAND_MAX)
yi = ymin + (ymax - ymin) * (rand2 / RAND_MAX)
zi = zmin + (zmax - zmin) * (rand3 / RAND_MAX)

u = (xi * xi) + (yi * yi) + (zi * zi)
;
; Create the output grid.
;
ii = fspan(0, 20.0, 21)
xo = xmin + (ii / (NX - 1)) * (xmax - xmin)
yo = ymin + (ii / (NY - 1)) * (ymax - ymin)
zo = zmin + (ii / (NZ - 1)) * (zmax - zmin)

;
; Interpolate.
;
u = dsgrid3(xi, yi, zi, u, xo, yo, zo)

end
```