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I've been trying to plot a simple heatmap using the 'plot with image' but since my data is not in a perfect square shape it is not working properly.

A warning issuing "warning: Visible pixel grid has a scan line shorter than previous scan lines." continued popping up every time i moved the chart or zoomed it, while the 'with image pixels' version produced a version of the heatmap that was rotated in a 3D space (why was this the case if the 'with image' mode is for a 2D plot only?)

my data is:

0.9882380255806047 0.9882380255806047 -0.7703887858517308
0.9882380255806047 0.9929170035354357 -0.03247814980870606
0.9882380255806047 0.9975959814902666 -0.6944306255482046
0.9882380255806047 1.0022749594450977 -0.746165843927831
0.9882380255806047 1.0069539373999286 -0.5151139695781666
0.9882380255806047 1.0116329153547596 -0.1838806386646351
0.9929170035354357 0.9929170035354357 -0.7703887858517308
0.9929170035354357 0.9975959814902666 -0.9227715329230436
0.9929170035354357 1.0022749594450977 -0.9171361902702745
0.9929170035354357 1.0069539373999286 -0.7797704881116272
0.9929170035354357 1.0116329153547596 -0.6650103546953546
0.9975959814902666 0.9975959814902666 -0.7703887858517308
0.9975959814902666 1.0022749594450977 -0.9065086173718683
0.9975959814902666 1.0069539373999286 -0.3481667020388293
0.9975959814902666 1.0116329153547596 0.10123715036482903
1.0022749594450977 1.0022749594450977 -0.7703887858517308
1.0022749594450977 1.0069539373999286 -0.28406345548617745
1.0022749594450977 1.0116329153547596 0.1835875555217213
1.0069539373999286 1.0069539373999286 -0.7703887858517308
1.0069539373999286 1.0116329153547596 -0.4920684723609338
1.0116329153547596 1.0116329153547596 -0.7703887858517308

how can i make it plot a simple heatmap even if some tiles would be missing? From what i've seen online having integer pixel coordinates shouldn't be a must, but maybe the sparsity is an issue(?)

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  • Please show your script and your resulting graph. Commented Aug 11, 2022 at 5:50

2 Answers 2

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2

You could also use the plotting style with boxxyerror to plot your heatmap (check help boxxyerror). If you have a regular grid and you don't want to manually tune the box size to get a fully colored area you can let gnuplot extract the minimum step size in x and y automatically.

Script:

### 2D heatmap with boxxyerrors and automatic boxsize
reset session

$Data <<EOD
0.9882380255806047 0.9882380255806047 -0.7703887858517308
0.9882380255806047 0.9929170035354357 -0.03247814980870606
0.9882380255806047 0.9975959814902666 -0.6944306255482046
0.9882380255806047 1.0022749594450977 -0.746165843927831
0.9882380255806047 1.0069539373999286 -0.5151139695781666
0.9882380255806047 1.0116329153547596 -0.1838806386646351
0.9929170035354357 0.9929170035354357 -0.7703887858517308
0.9929170035354357 0.9975959814902666 -0.9227715329230436
0.9929170035354357 1.0022749594450977 -0.9171361902702745
0.9929170035354357 1.0069539373999286 -0.7797704881116272
0.9929170035354357 1.0116329153547596 -0.6650103546953546
0.9975959814902666 0.9975959814902666 -0.7703887858517308
0.9975959814902666 1.0022749594450977 -0.9065086173718683
0.9975959814902666 1.0069539373999286 -0.3481667020388293
0.9975959814902666 1.0116329153547596 0.10123715036482903
1.0022749594450977 1.0022749594450977 -0.7703887858517308
1.0022749594450977 1.0069539373999286 -0.28406345548617745
1.0022749594450977 1.0116329153547596 0.1835875555217213
1.0069539373999286 1.0069539373999286 -0.7703887858517308
1.0069539373999286 1.0116329153547596 -0.4920684723609338
1.0116329153547596 1.0116329153547596 -0.7703887858517308
EOD

# find the smallest dx,dy > 0
stats $Data u ($0==0?(x0=$1,y0=$2):0, dx=abs(x0-$1), dx==0 ? NaN : dx) : \
              (dy=abs(y0-$2), dy==0 ? NaN : dy) nooutput
dx = STATS_min_x/2.
dy = STATS_min_y/2.

set palette rgb 33,13,10
set size ratio -1
set style fill solid 1.0
set key noautotitle

plot $Data u 1:2:(dx):(dy):3 w boxxy palette
### end of script

Result:

enter image description here

Addition:

Just for completeness, the automatic search for dx,dy>0 in the above script would fail with the data in the example below. The data below is (especially chosen) such that even if you (alternatively) compare the difference of two successive x (or y) values to find the minimum dx and dy it would fail. Hence you need a bit more effort.

  • plot the data into the temporary datablock $Temp by using the option smooth freqency (check help smooth frequency). With this you get unique values in ascending order. Do this for x-column and y-column.
  • since the sorted data for x and y in $Temp will be separated by two empty lines, you can address it via index (check help index).
  • use stats to calculate the difference between successive data points in $Temp and get the minimum in the variable STATS_min.

Script:

### 2D heatmap with boxxyerrors and automatic boxsize
reset session

$Data <<EOD
  1   3   1.5
  1   5   1.9
  3   1   3.1
  5   4   5.7
  5   1   5.1
  3   4   3.7
  1   4   1.7
  4   4   4.7
  4   1   4.1
  4   3   4.5
  4   5   4.9
  1   1   1.1
  5   3   5.5
  5   5   5.9
  3   3   3.5
  3   5   3.9
EOD

# find the smallest dx,dy > 0
set table $Temp
    plot $Data u 1:0 smooth freq
    plot $Data u 2:0 smooth freq
unset table
v1 = NaN
stats $Temp u (v0=v1,v1=$1,dv=v1-v0) index 0 nooutput
dx = STATS_min/2.
v1 = NaN
stats $Temp u (v0=v1,v1=$1,dv=v1-v0) index 1 nooutput
dy = STATS_min/2.

set palette rgb 33,13,10
set size ratio -1
set style fill solid 1.0 noborder
set key noautotitle

plot $Data u 1:2:(dx):(dy):3 w boxxy palette
### end of script

Result:

enter image description here

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2 Comments

Thanks! A very clever solution to a peculiar problem
@VoteAnthony You're welcome. Actually, I noticed that there might be special cases where this search procedure for minimal dx,dy will fail, because currently you are comparing distances only to the first datapoint. If this first point is "isolated", i.e. no data points in the adjacent row or column, the extracted dx,dy would be wrong. Maybe there is a smarter procedure which could account for that special case.
2

You may need to clarify exactly what you want, and what you know in advance about your data properties. For now I suggest you might try this and see if it comes close to what you intended:

set size ratio -1    # make sure that a square is really a square
unset key
set palette cubehelix negative
set pointsize 10     # adjust if needed to make the pixels touch
plot 'foo' using 1:2:3 with points pointtype 5 fillcolor palette

enter image description here

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