“pixel dimension information” when plotting with image in gnuplot

2
votes

Using gnuplot v5 patch 6 on windows 10 (wxt terminal)

I have a data file of 2D vectors arranged in six columns (x, y, v_x, v_y, v_mag, rho) that I'm trying to plot as a heatmap of v_mag against x and y. The plot generates fine, but it's always coming up with 

"No dimension information for 80000 pixels total. Try 200 x 400"

But I have no idea where to specify this in the terminal.

I realise that I can use pm3d map for this, but this doesn't work without setting dgrid3d and that causes problems with plotting dots on top of the heatmap which I'm also doing. I also don't want to generate a matrix file just for the image plot since I need the vector data for analysis later.

In terms of an example, the plot will generate if I literally just write:

plot 'vectors.dat' using 1:2:5 with image, 'dots.dat' with dots

EDIT: added 'set pm3d' to example code

EDIT: example is now minimal code to produce desired plot

EDIT: example data file can be found here

Any help would be appreciated.

1
gnuplotheatmap
Your data format is wrong. If you have matrix-like input you must separate isolines (two blocks with equal values in either first or second column, depending on your data file) by a single blank lines, see splot > Data-file > example datafile in the gnuplot documentation: gnuplotting.org/manpage-gnuplot-4-6/#Q1-1-742 – Christoph
Thanks for that information. I have made the changes (added a blank line between blocks with different y values), but it doesn't seem to have an effect. I neglected to mention that I'm using 'pm3d map'. Does this make a difference? – JHall
Do you need to use pm3d? It might be easier to to use the image plot style, see for example the second example in the heatmap demo. – user8153
The set pm3d has no effect in your script, because it is overridden by the with ... settings. Note, that both image and pm3d are quite different, but both require a regular grid (same number of points in every isoline), does your data have that? Then adding the blank lines should help you, if not you should show the data file for further investigation. – Christoph
You're sort of right about the pm3d line, I was just using it to get a top down view of the image. But This can be done by just using plot instead of splot. My data files are quite large, but I'll see if I can upload a smaller example. – JHall

1 Answers

4
votes

After updating my gnuplot to v5.2, this problem has disappeared.