IGRID

Purpose:

Grids irregular XYZ data to a uniform grid using the inverse distance method.

Syntax:

IGRID(x, y, z, gridsize, interp, weights, radius)

x	-	A series, the X or horizontal range.
y	-	A series, the Y or vertical range.
z	-	A series, the Z or height data.
gridsize	-	Optional. An integer or series, the size of output grid. Defaults to sqrt(length(x)).
interp	-	Optional. An integer, the cubic spline smoothing factor. Defaults to 1 (no smoothing).
weights	-	Optional. A series, the weights of distance function. Defaults to {0, 0, 1, 1, 1}.
radius	-	Optional. A real, the maximum radius to include in the interpolation. Defaults to -1, all.

Returns:

An array.

Example:

x = grand(100, 1)*2 - 1;

y = grand(100, 1)*2 - 1;

z = cos(x*y);

xyz = igrid(x, y, z);

Grids the function cos(x*y) over the range -1 to 1 with an interpolated grid of 11x11.

$image\igridpic.gif$

Example:

xyz2 = igrid(x, y, z, 20)

Same as above but the interpolated grid is 20x20.

Example:

xyz2 = igrid(x[..], y[..], z[..], {20, 30}, 3)

Same as above but the interpolated grid is 20x30 and the surface is further interpolated by a factor of 3 using cubic spline interpolation.

Example:

IGRID also accepts a single XYZ series as input:

xyzser = xyz(x, y, z)

xyz3 = igrid(xyzser)

Same as first example.

xyz3 = igrid(xyzser, 20)

Same as second example.

xyz3 = igrid(xyzser, {20, 30}, 3)

Same as third example.

xyz4 = igrid(xyzser, {20, 30}, 3, {0, 1})

Same as above except the classical inverse squared distance weighting function is used instead of the default.

Remarks:

IGRID uses INVDISTANCE, the inverse distance method of gridding irregularly spaced data.

If GRIDSIZE is a series, the first element specifies the output number of columns and the second element specifies the output number of rows.

The optional WEIGHTS series specifies the weighting of the radius terms:

{r^-1, r^-2, r^-3, r^-4, ...}.

The default of {0, 0, 1, 1, 1} specifies a linear combination of r^-3 + r^-4 + r^-5 terms. Use the series {0, 1} to specify the classical inverse squared distance weighting function.

See INVDISTANCE for algorithmic details.

IGRID

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