[Gnuplot-info] Multicolored 3D scatter plot

[Robyn S. <ro...@MI...>]

Hello,

I'd like to represent some 4D data and am having trouble convincing 
gnuplot to do it.  The data consists of locations in a 3-dimensional 
volume, e.g. (r, theta, phi), with a value associated with each 
location.  I'd like gnuplot to make a 3D scatter plot, color each point 
according to its value, and display a color scale.  From the manual it 
seemed like the way to do this would be:

set cbrange [range of values]
set log cb

to color points on a log scale, and then use palette cb to make the 
colors go as I want:

  splot "density31.dat" using 1:3:2 with points lt palette cb $4

(if you're curious, the positions are actually in spherical coordinates 
using a slightly different mapping than the one in gnuplot, hence the 
out-of-order columns.)

The problem is that palette cb will apparently only take a constant 
value as an argument, so the command above fails, giving me an 
"undefined value" error on the argument to palette cb.  (The command 
works fine if I replace the column argument $4 with a constant value, 
but then all the points are the same color.)  I can probably come up 
with a way to use "rgb variable" to do this, but then I don't get a 
color scale.

There were several similar questions to this already on the newsgroup 
but most of them had either no response or a minimal (and pessimistic 
one).  Is there a way to get the output I want from gnuplot (maybe with 
rgbformulae?) or should I give up and use a different program?

I have limited access to the newsgroup but if I am able to work out the 
method of doing this I'll summarize it and document it on my personal 
website and post a link to the group, so please reply by email to me.

Thanks very much,
R