GRID_2D Function

Reference Guide > G Routines > GRID_2D Function

GRID_2D Function

Returns a gridded, 1D array containing y values, given random x,y coordinates (this function works best with sparse data points).

Usage

result = GRID_2D(points, grid_x)

Input Parameters

points—A (2, n) array containing the random x,y points to be gridded.

grid_x—The size of the vector to return.

Returned Value

result—A gridded, 1D array containing y values.

Keywords

Order—The order of the weighting function to use for neighborhood averaging. Points are weighted by the function:

w = 1.0 / (dist ^ Order)

where dist is the distance to the point. (Default: 2)

XMax—The x-coordinate of the right edge of the grid. If omitted, maps the maximum x value found in the points(0, *) array to the right edge of the grid.

XMin—The x-coordinate of the left edge of the grid. If omitted, maps the minimum x value found in the points(0, *) array to the left edge of the grid.

Discussion

GRID_2D uses an inverse distance averaging technique to interpolate missing data values for 2D gridding. The gridded array returned by GRID_2D is suitable for use with the PLOT function.

GRID_2D is similar to FAST_GRID2. GRID_2D, however, works best with sparse data points (say, less than 1000 points to be gridded) and is stable when extrapolating into large void areas. (FAST_GRID2 works best with dense data points; it is considerably faster, but slightly less accurate, than GRID_2D.)

Examples

These commands show 2D gridding with sparse data points.

; Generate the data.

points = INTARR(2, 10)

points(*, 0) = [1,2]

points(*, 1) = [1,3]

points(*, 2) = [9,5]

points(*, 3) = [8,0]

points(*, 4) = [9,6]

points(*, 5) = [9,9]

points(*, 6) = [7,15]

points(*, 7) = [6,-5]

points(*, 8) = [0,3]

points(*, 9) = [0,-1]

; Reset the viewing window and load the color table.

WINDOW, 0, Colors=128

LOADCT, 4

T3D, /Reset

; Set the y-axis range for plotting.

!Y.Range = [MIN(points), MAX(points)]

; Grid and plot the resulting data.

yval = GRID_2D(points, 256, Order=0.5)

PLOT, yval, Color=WoColorConvert(60)

yval = GRID_2D(points, 256, Order=1.0)

OPLOT, yval, Color=WoColorConvert(80)

yval = GRID_2D(points, 256, Order=2.0)

OPLOT, yval, Color=WoColorConvert(100)

yval = GRID_2D(points, 256, Order=3.0)

OPLOT, yval, Color=WoColorConvert(120)

; Reset the y-axis range to the default value.

!Y.Range = [0.0, 0.0]