Tikz: get the point at the arc end

Question

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]
\newcommand{\xradius}{0.22}
\newcommand{\yradius}{0.17}
%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 (center) circle [x radius=\xradius, y radius=\yradius, rotate=\myrotation]; %Drawing black ellipse

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

\draw [color=red] (startpoint) arc [x radius=\xradius, y radius=\yradius, start angle={-90}, delta angle={90-\myangle/2}, 
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}

Oh, yes, thanks in advance for the answers.

Answer 1

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]
  \newcommand{\xradius}{0.22}
  \newcommand{\yradius}{0.17}
  %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[rotate=\myrotation] (center) circle [x radius=\xradius, y radius=\yradius];
  \path[rotate=\myrotation] (center) ++(-90:\yradius) coordinate (startpoint); 
  \draw [color=red,rotate=\myrotation] (startpoint) 
    arc [x radius=\xradius, y radius=\yradius, start angle={-90}, delta angle={90-\myangle/2}] 
    coordinate (mypoint);
  \path [fill=green, radius=0.02] (mypoint) circle;
  \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]
  \newcommand{\xradius}{0.22}
  \newcommand{\yradius}{0.17}
  %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 (center) circle [x radius=\xradius, y radius=\yradius];
    \path (center) ++(-90:\yradius) coordinate (startpoint); 
    \draw [color=red] (startpoint) 
      arc [x radius=\xradius, y radius=\yradius, start angle={-90}, delta angle={90-\myangle/2}] 
      coordinate (mypoint);
    \draw [help lines] (center) -- +({4*\xradius},0);
  \end{scope}

  \path [fill=green, radius=0.02] (mypoint) circle;
\end{tikzpicture}
\end{document}

Answer 2

Compiling your MWE results in this:

Seems to me that the green spot is spot on!