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List:       gnuplot-info
Subject:    RE: gnuplot contour plots
From:       "crawford" <crawford () arete ! com>
Date:       2002-05-30 15:26:56
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On Wednesday, May 29, Willie Martin wrote:

>Hello, I'm a programmer for NRL @ stennis.
>I'm currently using gnuplot and trying to get it to do a contour plot but
it say...
>cannot contour non grid data, what does this mean and what is the correct
format for >grid data used in a matrix?

In order for gnuplot to plot contours or a surface, it must have data
arranged as a "logical grid".  In a file, that looks like this:

x00  y00  z00
x01  y01  z01
x02  y02  z02
...
x0N  y0N  z0N
[blank line]
x10  y10  z10
x11  y11  z11
x12  y12  z12
...
x1N  y1N  z1N
[blank line]
x20  y20  z20
x21  y21  z21
x22  y22  z22
...
x2N  y2N  z2N
[blank line]
and so on.  The important thing to note is that each "datablock" (a group of
consecutive input records, terminated by a blank line) must have the same
total number of points.

gnuplot does not require that all the x's in a datablock be the same, so it
cannot know when the last point in a datablock has been read.  Thus the
blank line.

The "cannot contour non grid data" message means simply that the data in the
file are not organized in this manner.

You can read a bit more about this in "help splot data-file".

Dick Crawford, aka crawford@arete.com

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