# Cylinders in LaTeX the Easy and Correct Way

Drawing cylinders in vector graphic is a common task. It is less trivial as it looks at first glance, due to the challenge of finding a proper projection. In this post, I share a simple and robust recipe using the tikz-3dplot package of LaTeX. As opposed to many examples shared online, this approach automatically identifies the boundary of a cylinder, under a given perspective. The trick is to identify edges using the azimuth angle in cylindrical coordinates 馃挭.

\documentclass{standalone}
\usepackage{tikz,tikz-3dplot}
\begin{document}

\def\rotx{70}
\def\rotz{110}
\tdplotsetmaincoords{\rotx}{\rotz}
\begin{tikzpicture}[tdplot_main_coords]
\tikzstyle{every node}=[font=\small]
\draw[ultra thin,-latex] (0,0,0) -- (6,0,0) node[anchor=north east]{$x$};
\draw[ultra thin,-latex] (0,0,0) -- (0,6,0) node[anchor=north west]{$y$};
\draw[ultra thin,-latex] (0,0,0) -- (0,0,6) node[anchor=south]{$z$};
\draw [thick](0,0,4) circle (3);
\begin{scope}[canvas is xy plane at z=0]
\draw[thick, dashed] ([shift=(\rotz:3)] 0,0,0) arc (\rotz:\rotz+180:3);
\draw[thick] ([shift=(\rotz:3)] 0,0,0) arc (\rotz:\rotz-180:3);
\end{scope}
% manual edges
\draw [dotted, red](1.9,-2.34,0) -- (1.9,-2.34,4) node[midway, left]{};
\draw [dotted, red](-1.9,2.35,0) -- (-1.9,2.35,4);
% automatic edges !
\pgfcoordinate{edge1_top}{ \pgfpointcylindrical{\rotz}{3}{4} };
\pgfcoordinate{edge1_bottom}{ \pgfpointcylindrical{\rotz}{3}{0} };
\draw[thick] (edge1_top) -- (edge1_bottom);
\pgfcoordinate{edge2_top}{ \pgfpointcylindrical{\rotz+180}{3}{4} };
\pgfcoordinate{edge2_bottom}{ \pgfpointcylindrical{\rotz+180}{3}{0} };
\draw[thick] (edge2_top) -- (edge2_bottom);
\end{tikzpicture}

\end{document}

And we can enjoy this output, comparing with manual edges adapted from this post: