# Tikz: get the point at the arc end

When I draw an arc I get, through the coordinate command, the point at the end of the arc (mypoint in the code below) for further drawing, but it does not correspond to the expected point.

See the drawing: the green circle should lay at the end of the red arc (where I have placed manually a blue circle), as expected in the code, but it lays some millimetres away.

How could I get the "right" point at the end of the arc for further drawing?

Here is my code:

\documentclass[tikz, border=0.3cm]{standalone}
\usepackage{tikz}

\begin{document}

\begin{tikzpicture}[scale=1.5]
%Ellipses centre
\newcommand{\xcent}{2}
\newcommand{\ycent}{2}

\newcommand{\myrotation}{20} %Ellipse rotation angle
\newcommand{\myangle}{30} %Angle before axis

\coordinate (center) at (\xcent, \ycent);

\path (center) ++({-90+\myrotation}:\yradius) coordinate (startpoint); %Starting point of red arc

rotate=\myrotation] coordinate (mypoint);  %Drawing red arc and getting the end point
\path [fill=green, radius=0.02] (mypoint) circle; %Drawing green circle

\draw [help lines] (center) -- +(\myrotation:{4*\xradius}); %Gray reference axis

\end{tikzpicture}

\end{document}


The following suggestions will work with both the current pgf version (3.0.1a) and the old version 2.10.

Use rotate=\myrotation as option for the whole path:

\documentclass[tikz, border=0.3cm]{standalone}
\begin{document}
\begin{tikzpicture}[scale=1.5]
%Ellipses centre
\newcommand{\xcent}{2}
\newcommand{\ycent}{2}

\newcommand{\myrotation}{20} %Ellipse rotation angle
\newcommand{\myangle}{30} %Angle before axis

\coordinate (center) at (\xcent, \ycent);
\draw [color=red,rotate=\myrotation] (startpoint)
coordinate (mypoint);
\draw [help lines] (center) -- +(\myrotation:{4*\xradius});
\end{tikzpicture}
\end{document}


Or using a scope for the rotation:

\documentclass[tikz, border=2pt]{standalone}
\begin{document}
\begin{tikzpicture}[scale=1.5]
%Ellipses centre
\newcommand{\xcent}{2}
\newcommand{\ycent}{2}

\newcommand{\myrotation}{20} %Ellipse rotation angle
\newcommand{\myangle}{30} %Angle before axis

\coordinate (center) at (\xcent, \ycent);

\begin{scope}[rotate=\myrotation]
\draw [color=red] (startpoint)
coordinate (mypoint);
\draw [help lines] (center) -- +({4*\xradius},0);
\end{scope}


• Amazing! the trick of using rotate=\myrotation for the whole path did it. Thanks again @esdd! By the way, nice suggestion of creating a scope for the rotation, that's what I'll use! :) – loved.by.Jesus Dec 9 '15 at 11:54