interpolation artifacts in gnuplot

Question

I am currently writing a paper for my Degree and I have a problem with 3 Graphs that I am trying to plot using Gnuplot.

I got some data points which look like this:

...
100.000000   0.120000   2.000000   0.052724 6682.801488 
100.000000   0.130000   2.000000   0.055570 6805.632674 
100.000000   0.140000   2.000000   0.058270 6912.462994 
100.000000   0.150000   2.000000   0.060815 7006.219537 
100.000000   0.160000   2.000000   0.063252 7098.284918 
100.000000   0.170000   2.000000   0.065541 7621.135706 
100.000000   0.180000   2.000000   0.067744 8383.880473 
100.000000   0.190000   2.000000   0.069822 9030.334374 
100.000000   0.200000   2.000000   0.071812 9574.679479 
100.000000   0.210000   2.000000   0.073712 10001.423400 
100.000000   0.220000   2.000000   0.075520 10324.290168 
100.000000   0.230000   2.000000   0.077267 10577.919498 
100.000000   0.240000   2.000000   0.078932 10731.859176 
100.000000   0.250000   2.000000   0.080537 10781.566931 
100.000000   0.260000   2.000000   0.082081 10687.175109 
100.000000   0.270000   2.000000   0.083562 10580.855944 
100.000000   0.280000   2.000000   0.085001 10526.856376 
100.000000   0.290000   2.000000   0.086381 10581.738511 
100.000000   0.300000   2.000000   0.087723 10731.950591 
100.000000   0.310000   2.000000   0.089018 10909.067948 
100.000000   0.320000   2.000000   0.090281 11099.323889 
100.000000   0.330000   2.000000   0.091511 11296.953911 
100.000000   0.340000   2.000000   0.092710 11499.793402 
100.000000   0.350000   2.000000   0.093879 11702.881224 
...

where the first column represents my x-values ranging from [100-1000] in steps of 10. The second column displays my y-values ranging from about [0-3] in steps of 0.01.

I am trying to plot the third column as a 2d color plot.

But for some reason I get these artifacts. I tried adjusting the grid size up and down. Here is my code:

### interpolate data with highlighted datapoints
reset session

#set terminal postscript eps enhanced color font 'Helvetica,10'

# ---------------------------------------------------------------------------------------
#set output './production/SpeedKraft.eps'

set title "" 

set xrange [100:1000]
set yrange [0.01:2.5]

set xlabel "" 
set ylabel "" rotate by 90

# ---------------------------------------------------------------------------------------


set palette grey
set grid
set size square
set view map
set pm3d at b
# set pm3d interpolate 2,2
set dgrid3d 1000,1000 qnorm 2
set table $DataInterpolated
    splot "SpeedNeu.dat" u 1:2:3 
unset table
unset dgrid3d

set format y "%.1f"
set format x "%.0f"



splot $DataInterpolated u 1:2:3 w pm3d palette notitle, \
    #  "Speed.dat" u 1:2:3 w p pt 1 lw 2 lc rgb "black" notitle

### end of code

I am very happy if someone could help me out on this one!

Regards Finn

Answer 1

Using dgrid3d to create an interpolated 3D surface seems more likely to obscure the data structure by overfitting than it is to enlighten. Have you tried the much simpler

plot "SpeedNeu.dat" using 1:2:3 with image

or even

plot "SpeedNeu.dat" using 1:2:3 with points pt 5 lc palette

Edited to show handling of missing points and space between points

set pointsize 7.2   # exact size found by experimentation
                    # I left a tiny gap so you can see it, 7.3 would remove it
set size square
set colorbar user origin 0.9,0.2 size 0.05,0.6
unset border; unset tics; unset key
plot "fake.data" using 1:2:3 with points pt 5 lc palette