[Gnuplot-info] plotting 4 column data

[Ashenafi D. <ash...@gm...>]

HI,

I have a problem plotting some 4-column data. The 1st and 2nd column are x-
and y-axes. The 3rd column has values which I used the 'set pm3d map' and
'set palette' to have different colors for different values. so basically I
can do a surface plot using the three columns, the 3rd column identified by
its color and not an axis. Now I want to put the values of the 4th column on
top of what I have. The values of the 4th column are mostly very close to
zero except for a couple of grid points on the x-y plane. If the 4th column
has a value different from zero, it will be, say, eithe -1 or +1. So what I
want to do is to put a circle or whatever symbol for points for which the
value of the 4th column is different from zero on top of the plot (which is
actually an splot) which I obtain from the first three columns. I think
there is a way to do it in gnuplot. Can someone help me out with that?

Many thanks,
Dadi
P.S. I'm using version 4.2 of gnuplot.