# Concentric Cylinders with tikz

I am trying to draw two concentric cylinders with tikz to show the change in volume with respect to radius, while the height remains fixed. The left ilustration below is the first drawing, where the height changes with fixed radius. Much of this code was borrowed from here. The illustration at the right is where I have questions. 1) Is there a way to shade the region between the two top bases? I know how to do this for a regular 2-d illustration using tikz rules between regions, but I can't quite reference these two separate bases.

2) This illustration isn't ideal, obviously, so would there be a more efficient way to generate it where the cylinders appear truly concentric? Perhaps manually draw a similar ellipse inside the outer cylinder and experiment with placement?

the MWE is:

\documentclass[border=5pt]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,snakes,backgrounds,patterns,shapes.geometric,calc}

\begin{document}

\begin{tikzpicture}[scale=1]
\node [draw, cylinder, cylinder uses custom fill, cylinder body fill=lightgray!20,
cylinder end fill=lightgray!20, shape aspect=4, rotate=90, minimum width=3cm] (c1) at
(0,1.8){};

\coordinate(dhtop) at ($(c1.after top)!-1*.1!(c1.before top)$);
\coordinate(dhbot) at ($(c1.before bottom)!-1*.1!(c1.after bottom)$);
\coordinate(dhlabel) at ($(dhtop)!.5!(dhbot)$);
\draw[|-|] (dhbot)--(dhtop);
\path (dhlabel) node[right, outer sep = 2pt] {$dh$};

\node [draw, cylinder, shape aspect=4, rotate=90, minimum height=4cm, minimum
width=3cm] (c) {};

\coordinate(htop) at ($(c.before top)!-1*.1!(c.after top)$);
\coordinate(hbot) at ($(c.after bottom)!-1*.1!(c.before bottom)$);
\coordinate(hlabel) at ($(htop)!.5!(hbot)+(c.north)!.9!(c.center)$);

\draw[|-|] (hbot)--(htop);
\path (hlabel) node[left] {$h$}; %Modify height label here

\coordinate (center) at ($(c.before top)!0.5!(c.after top)$);
\filldraw (center) circle (1pt);

\coordinate (rlabel) at ($(center) !0.5!(c.after top)$);
\coordinate (rtop) at ($(center)!-1*.1!(c.after top)$);

\coordinate (rend) at ($(c.mid east)!0.5!(c.after top)$);
\draw[-, shorten >=-10] (center) -- (rend);
\path (rend) node[outer sep = 5pt, left] {$r$};
\end{tikzpicture}

\bigskip

\begin{tikzpicture}[scale=1]
\node [draw, cylinder, shape aspect=6, rotate=90, cylinder uses custom fill, cylinder
body fill=lightgray!20, minimum height=4cm, minimum width=4cm] (c1) at (0,0){};

\coordinate(htop) at ($(c1.after top)!-1*.1!(c1.before top)$);
\coordinate(hbot) at ($(c1.before bottom)!-1*.1!(c1.after bottom)$);
\coordinate(hlabel) at ($(htop)!.5!(hbot)$);
\draw[|-|] (hbot)--(htop);
\path (hlabel) node[right, outer sep = 2pt] {$h$};

\node [draw, cylinder, shape aspect=5, rotate=90, minimum height=3.9cm, minimum
width=3cm] (c) {};

\coordinate (center) at ($(c.before top)!0.5!(c.after top)$);
\filldraw (center) circle (1pt);

\coordinate (rlabel) at ($(center) !0.5!(c.after top)$);
\coordinate (rtop) at ($(center)!-1*.1!(c.after top)$);

\coordinate (rend) at ($(c.mid east)!0.5!(c.after top)$);
\draw[-, shorten >=-10] (center) -- (rend);
\path (rend) node[outer sep = 5pt, left] {$r$};
\end{tikzpicture}

\end{document}

• If you create a path which goes around one arc 360^\circ and back the other arc 360^\circ to form a closed path, you should be able to shade it. Or, you could shade the big ellipse then fill the inner ellipse with color=white to erase it again. Oh, and you need to maintain the same ratio of x to y radii for both ellipses. – John Kormylo Oct 8 '14 at 2:38
• The cylinders are generated as one "piece" - perhaps I can reference the built in anchors to create the ellipses? – Abbas Jaffary Oct 9 '14 at 13:12

In Metapost, you can shade an annulus by filling the outer circle with the shade and then filling the inner circle with the background. Here's an attempt at your figure, which might give you a starting point. prologues := 3;
outputtemplate := "%j%c.eps";

beginfig(1);

path c, d, r, h;

p = 89; q = 34;
c = fullcircle xscaled p yscaled q;
d = c scaled 1.4;

fill d withcolor .9 white;
fill c withcolor white;

forsuffixes $=c,d: draw$;
draw point 4 of $-- subpath (4,8) of$ shifted (0,-p) -- point 0 of $; draw subpath (0,4) of$ shifted (0,-p) dashed withdots scaled .4;
endfor

r = origin -- point 1 of c;
draw r; label.ulft(btex $r$ etex, point 0.5 of r);
fill c scaled 1/25;

h = (point 0 of d -- point 0 of d shifted (0,-p)) shifted 20 right;
ahangle := 180; ahlength := 3;
drawdblarrow h; label.rt(btex $h$ etex, point 0.5 of h);

endfig;
end.

• Thank you this is a perfect drawing. Thank you also for the link, I haven't used Metapost but will start learning. – Abbas Jaffary Oct 9 '14 at 13:16