Gnuplot zrange change with pm3d

Question

I have a data, when I plot with a line plot I get the correct minima and zrange. Depicted below LINE plot with correct zrange

set ticslevel 0
spl 'surf_laplace3.dat' w l 

However, when I use pm3d the range automatically changes and so the minima. pm3d plot

set pm3d
set dgrid3d 300,300
set ticslevel 0
splot 'surf_laplace3.dat' w pm3d 

if I use less thatn 300,300 in dgrid3d.. the density map is even low dat file is here Can anyone help me out ?

Answer 1

This has nothing to do with pm3d, but is caused by dgrid3d. This option will cause gnuplot to interpolate the data on a 300x300 grid. Depending on the interpolation function this will change your data points.

Because your data points already form a complete grid you should not use dgrid3d at all. All you need to do is to make clear to gnuplot when a new row in your data starts (i.e., when the x-value changes). You can do this by adding a blank line every 301 lines in your data file. Then you get the right result simply from

splot "surf_laplace3.dat" w pm3d