Putting a circle with pm3d map

Question

I made a density plot using pm3d map. The plot is great (as expected) but now I need to put a circle (a circumference I mean) with centre at the origin and a given radius (three in my case).

I tried defining the function: f(x)=sqrt(9.-x**2) and adding to the plot: splot 'file.dat' u 1:2:3 with pm3d, f(x),-f(x) but the result is disastrous (as I suspected). Is there any way to add a circle to the plot without distorting it ???

Many thanks.

Answer 1

Have a look at set object:

set object circle at 0,0 size 1
plot x