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[GREG2\]RANDOM_MAP [Arg1 [Arg2]] [/NEIGHBOURS Nb] [/TRIANGLES] [/EX-
TRAPOLATE] [/BLANKING Bval] [VARIABLES Vx Vy Vz]
This command is a general purpose interpolation task which uses data
from the X, Y and Z arrays (or those specified in option /VARIABLEs) to
fill in a Regular Grid array representing the same surface Z=f(X,Y) by
an interpolation process. X, Y and Z are arrays defined by the COLUMN
command (see HELP COLUMN). It triangulates the data for interpolation.
If a triangulation already exists, and only the Z array has been
changed, RANDOM_MAP does not make a new triangulation.
Often, the user-provided Z=f(X,Y) surface is REGULARLY SAMPLED, even if
NOT COMPLETELY SAMPLED. In this case, it is recommended to use directly
the RGDATA command to create a Regular-grid map, since RANDOM is known
to perform awkwardly with regularly sampled data.
The interpolated grid can be defined by the arguments. If Arg1 is
"RGMAP", the interpolated grid will be exactly coincident with the cur-
rent Regular Grid array, else Arg1 and Arg2 are used to indicate the
number of pixels in X and Y directions and Arg2 = Arg1 if not specified.
Note that several hypothesis are made about the geometry of triangles in
the plot page space (hence the geometry may be changed by changing the
LIMIT or the BOX_LOCATION). You should thus use limits which gives a
reasonable representation of what are the neighbours of a given data
point. Moreover, this is an interpolation process. Hence if the basic
sampling theory is not respected by your choice of input data points and
output grid, spurious oscillations may occur in the resulting grid.