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(gnuplot.info)dgrid3d

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Enter node , (file) or (file)node

 The `set dgrid3d` command enables, and can set parameters for, non-grid
 to grid data mapping.

 Syntax:
       set dgrid3d {<row_size>} {,{<col_size>} {,<norm>}}
       set nodgrid3d
       show dgrid3d

 By default `dgrid3d` is disabled.  When enabled, 3-d data read from a file
 are always treated as a scattered data set.  A grid with dimensions derived
 from a bounding box of the scattered data and size as specified by the
 row/col_size parameters is created for plotting and contouring.  The grid
 is equally spaced in x (rows) and in y (columns); the z values are computed
 as weighted averages of the scattered points' z values.

 The third parameter, norm, controls the weighting:  Each data point is
 weighted inversely by its distance from the grid point raised to the norm
 power.  (Actually, the weights are given by the inverse of dx^norm + dy^norm,
 where dx and dy are the components of the separation of the grid point from
 each data point.  For some norms that are powers of two, specifically 4, 8,
 and 16, the computation is optimized by using the Euclidean distance in the
 weight calculation, (dx^2+dx^2)^norm/2.  However, any non-negative integer
 can be used.)

 The closer the data point is to a grid point, the more effect it has on
 that grid point and the larger the value of norm the less effect more
 distant data points have on that grid point.

 The `dgrid3d` option is a simple low pass filter that converts scattered
 data to a grid data set.  More sophisticated approaches to this problem
 exist and should be used to preprocess the data outside `gnuplot`
 (Note: gnuplot ) if this simple solution is found inadequate.

 (The z values are found by weighting all data points, not by interpolating
 between nearby data points;  also edge effects may produce unexpected and/or
 undesired results.  In some cases, small norm values produce a grid point
 reflecting the average of distant data points rather than a local average,
 while large values of norm may produce "steps" with several grid points
 having the same value as the closest data point, rather than making a smooth
 transition between adjacent data points.  Some areas of a grid may be filled
 by extrapolation, to an arbitrary boundary condition.  The variables are
 not normalized; consequently the units used for x and y will affect the
 relative weights of points in the x and y directions.)

 Examples:
       set dgrid3d 10,10,1     # defaults
       set dgrid3d ,,4

 The first specifies that a grid of size 10 by 10 is to be constructed using
 a norm value of 1 in the weight computation.  The second only modifies the
 norm, changing it to 4.