We would like to intersect a 3D plot with a plane. The problem is not to get the two functions into a plot, but to get the two functions to visual intersect with each other, i.e the nearest surface is in the foreground.

This can’t be done automatically, unfortunately, since pgfplots can’t do z buffering between different addplot commands.

For this concrete application, you could construct the plot “by hand”, however:

First, you draw the part of the cone below 0, then you draw the plane and the circle, then you draw the part of the cone above 0.

I’ve used a polar coordinate system for this, since it makes the input of polar functions easier.

This code was written by Jake on TeX.SE.

\documentclass[border=10pt]{standalone} \usepackage{pgfplots} \pgfplotsset{width=7cm,compat=1.8} \begin{document} \begin{tikzpicture} \begin{axis}[grid=major,view={20}{40},z buffer=sort, data cs=polar] \addplot3 [surf, domain=0:360, domain y=5:10,samples=30, samples y=10] {-y+5}; \addplot3 [data cs=cart,surf,domain=-10:10,samples=2, opacity=0.5] {0}; \addplot3 [domain=0:360, samples y=0, samples=30, thick, z buffer=auto] (x,5.1,0); \addplot3 [surf,domain=0:360, domain y=0:5,samples=30, samples y=10] {-y+5}; \end{axis} \end{tikzpicture} \end{document}