Gnuplot how to plot a 3d surface given coordinates?

Question

3D

There is such a coordinate file. https://pastebin.pl/view/98a08e81

...
0 237 5
0 238 5
0 239 5
0 240 1
0 241 1
0 242 1
0 243 1
...

Where is the x, y, z coordinate. I want to get the view surface.



I do

gnuplot> set pm3d
gnuplot> splot "./res.txt"

I get



Plus another error:

Warning: Single isoline (scan) is not enough for a pm3d plot.
Hint: Missing blank lines in the data file? See 'help pm3d' and FAQ.

If you set

splot "./res.txt" with pm3d

That, it doesn't draw anything at all.

What am I doing wrong and how do I get a decent result with color changing depending on the z-height?