gnuplot surface with non-grid data

[mattia.tamellini]

Hello everyone!


I have a problem that has been driving me mad for the whole day. Basically, I need to plot a 3D data series as a 2D heat map with GNUPlot.


If I had a structured mesh, I could arrange the output of my simulation like:

x_1 y_1 z_11
x_1 y_2 z_12
..
x_1 y_n z_1n


x_2 y_1 z_21
..
x_2 y_n z_2n


..


x_m y_1 z_m1
..
x_m y_n z_mn


and then I could get what I want with

set terminal png
set output "out.png"
set view map
splot "grid_data.txt" with pm3d pal notitle


(am I wrong?)


The problem is that my data are not arranged in a grid, since I do not have the same number of points for every x.


So I added the command "set dgrid3d" to the gnuplot script above in order to be able to plot non-grid data as a heat map. And here I get to my questions:
1) how should I arrange my data for such a plot? I am currently using this format:

x_1 y_1 z_1
x_2 y_2 z_2
x_3 y_3 z_3
x_1 y_1 z_1


x_4 y_4 z_4
x_5 y_5 z_5
x_6 y_6 z_6
x_4 y_4 z_4


...
(that is: I am dividing my data in blocks, with every block containing the coordinates of the vertices of every triangle in the mesh and the value of the solution in such vertex). Is that right or is there a better way?


2) the command "set dgrid3d" is particularly slow, and with a file of a million lines (roughly 50 MB) it fills up all of my RAM (8 GB) and freezes my laptop, forcing me to kill the process. Is there a faster way to plot non-grid data? Or am I doing something completely wrong, and this is not the way one plots non-grid data with gnuplot?


3) should I change software at all? :)


I'm starting to think that I have missed something about gnuplot.


Thanks a lot!!