next up previous contents index
Next: RANDOM_MAP /BLANKING Up: GREG2 Language Internal Help Previous: PROJECTION   Contents   Index


RANDOM_MAP

        [GREG2\]RANDOM_MAP [Arg1 [Arg2]] [/NEIGHBOURS Nb] [/TRIANGLES] [/EX-
    TRAPOLATE] [/BLANKING Bval]

    This command is a general purpose interpolation  task  which  uses  data
    from  the X, Y and Z arrays 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 triangula-
    tion.

    Usually, the user-provided Z=f(X,Y) surface is REGULARLY  SAMPLED,  even
    if NOT COMPLETELY SAMPLED. In this case, one SHOULD USE directly the RG-
    DATA command to create a Regular-grid map, since RANDOM is known to per-
    form 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.


Subsections

Gildas manager 2011-09-07