TeX - LaTeX Stack Exchange is a question and answer site for users of TeX, LaTeX, ConTeXt, and related typesetting systems. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

There's something strange going on with the animation at 135 degrees. I can't figure out what's going wrong.

enter image description here

Here's the MWE:


            \draw[fill]  (0,0) coordinate [label=180:Z] (Z) circle (2pt);           %% center of the picture
            \draw[fill]  (5,5) coordinate [label=135:Q] (Q) circle (2pt);           %% center of the circle
            \draw[fill]  (Q) -- +(  0:6)   coordinate [label=0:A] (A) circle (2pt); %% first point on the circle
            \clip[draw] (Q)  circle (4.5cm);
            \draw[help lines,blue!20,step=1] (0,0) grid (12,12);
            %% drawing the circle
            \draw[blue]  (A) 
                         let \p1 = ($ (A) - (Q) $) in

            \draw [line width=0.4pt,red]
                  let \p1 = ($(A) - (Q)$), \n1={veclen(\x1,\y1)} in
                  (Q) -- +(#1:\n1)
                  coordinate (B) circle (2pt);

            \draw[purple,line width=0.4pt] 
                  (B) -- +($  (0,0) ! 2em ! 0 : ($(B)-(Q)$)  $)  
                  coordinate [label=center:{\textbf{B:#1}}] (Bl) circle (2em);

                  ($ (B) ! 0.45 ! (Q) $) 
                  coordinate (tC) circle (2pt);

            \draw[line width=01.5em,->]
                  let \p1 = ($(tC) - (Q)$), 
                      \n1={atan2(\x1,\y1)}, %% start angle
                      \n2={\n1+90},         %% end angle
                      \n3={veclen(\x1,\y1)} %% radius
                      arc (\n1:\n2:\n3)
                      -- ++(\n2+80:1em)



share|improve this question
Hm, interesting. Anyway, why don’t you just use #1 for \n1? You probably could also simplify a lot more … – Qrrbrbirlbel Feb 17 '13 at 3:15
@GarbageCollector. What did you do to get the animation to work? – A.Ellett Feb 17 '13 at 3:41
@A.Ellett (You might remove the animating bit as it has nothing to do with problem.) The culprit seems to be the divide function of PGF math. Check the output of \pgfmathparse{33.19675/-33.19678}\pgfmathresult and vary the divisor’s last digit. It jumps from -1.0 (last digit: 5) to -0.1 (6 to 8) to -0.99998 (9). – Qrrbrbirlbel Feb 17 '13 at 5:22
@Qrrbrbirlbel This bug is fixed in the current CVS version of TikZ/PGF. – Paul Gaborit Feb 17 '13 at 8:32
@PaulGaborit You are right. The \pgfmathdivide@@ macro has been patched (with the help of a few others). Changelog of 2011-04-18. @A.Ellett Maybe it is time for you to update to the CVS version after all … – Qrrbrbirlbel Feb 17 '13 at 8:42

There is no angle discontinuity in PSTricks.

enter image description here


        (!1 \i\space 45 add PtoC){Head}
share|improve this answer
There is no TikZ in PSTricks. ;) – Qrrbrbirlbel Feb 17 '13 at 4:47
I love the answer, but unfortunately I already know how to do this in pstricks. My objective was to learn how to use tikz. Nevertheless, great answer! – A.Ellett Feb 17 '13 at 4:57
Actually, there's a bit of syntax in your answer I'm not familiar with. What are you doing when you write ([nodesep=2.8]{Tail}Q}{C}? Actually, I can see it's a translation, but where is it documented? – A.Ellett Feb 17 '13 at 5:52
@A.Ellett: It represents a node which is 2.8 apart from Q node in the direction of a vector from Q node to Tail node. It is documented in pstricks-doc.pdf on page 147. Use texdoc pstricks-doc to open the documentation. – kiss my armpit Feb 17 '13 at 6:44

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.