# How to draw \psellipticarc?

\documentclass[pstricks,border=12pt]{standalone}
\begin{document}
\begin{pspicture}[showgrid](-1,-1)(4,4)
\psellipticarc[showpoints]{->}(.5,0)(1.5,1){215}{0}
\psarc*[showpoints](1.5,1.5){1.5}{215}{0}
\end{pspicture}
\end{document}


Update:

\documentclass[pstricks,border=12pt]{standalone}
\begin{document}
\begin{pspicture}[showgrid](-1,-1)(4,4)
\psarc*[showpoints](1.5,1.5){1.5}{215}{0}
\psellipticarc[showpoints]{->}(.5,0)(1.5,1){215}{0}
\end{pspicture}
\end{document}


It produces true result

Question:

How to fix it?

How to the star version be more beautiful?

\documentclass[pstricks,border=12pt]{standalone}
\begin{document}
\begin{pspicture}[showgrid](-1,-1)(4,4)
%
\psellipticarc[linecolor=red,correctAngle=false]{->}(1,2)(1,2){215}{0}
\rput(1,2){%
\psset{linestyle=dashed}%
\psline(!1 2 215 PtoCab)(0,0)%
\psline(0,0)(!1 2 0 PtoCab)}
%
\psarc*(3,3){1}{215}{0}
\rput(3,3){%
\psset{linestyle=dashed}%
\psline(!1 215 PtoC)(0,0)%
\psline(0,0)(!1 0 PtoC)}
\end{pspicture}
\end{document}


# About correctAngle

An ellipse can be parameterized as x=a cos t and y= b sin t where t is a parameter that does not represent an angle relative to the x axis.

If you write, for example \psellipticalarc(0,0)(1,2){0}{45} with the default correctAngle=true then it draws an elliptical arc that starts from 0 degrees to 45 degrees.

However, if you write, for example \psellipticalarc[correctAngle=false](0,0)(1,2){0}{45} then it draw an elliptical arc that starts from 0 degrees to arctan(2) degrees. Here 45 does not represent an angle relative to the x axis.

Thus, correctAngle=true can be read as "make the parameter as a real angle".

With pstricks.tex from http://archiv.dante.de/~herbert/texnik/tex/generic/pstricks/

\documentclass[pstricks,border=12pt]{standalone}
\begin{document}
\begin{pspicture}[showgrid](-1,-1)(5,4)
\psarc[showpoints](0.25,0.5){1.5}{215}{0}
\psarc*(3.25,2){1.5}{215}{0}
\psarc(3.25,0.5){1.5}{215}{0}
\psarc*[showpoints](0.25,2){1.5}{215}{0}
\psellipticarc[showpoints,linecolor=red](0,3)(1.5,1){215}{0}
\psellipticarc*[showpoints,linecolor=red](0,4)(1.5,1){215}{0}
\psellipticarc[linecolor=red](3,3)(1.5,1){215}{0}
\psellipticarc*[linecolor=red](3,4)(1.5,1){215}{0}
\end{pspicture}
\end{document}


For correctAngle read http://mirrors.ctan.org/graphics/pstricks/base/doc/pst-news10.pdf section 3.4, page 8

• With \psarc*[showpoints](0.25,2){1.5}{215}{0} and \psellipticarc*[showpoints,linecolor=red](0,4)(1.5,1){215}{0} , it poduces dash line belong black area. Ugly. How to ignore it? – Trong Vuong Dec 29 '18 at 14:12
• It is obviously, that showpoints will draw the help lines. Do not use it if you do not want it! – user2478 Dec 29 '18 at 14:54
• @Herbert \psarc*(1.5,1.5){1.5}{215}{0} \psarc[showpoints](1.5,1.5){1.5}{215}{0} are more beautiful \psarc*[showpoints](1.5,1.5){1.5}{215}{0}. Are you ok? – Trong Vuong Dec 29 '18 at 15:04
• I already wrote: That are help lines to see where the origin is. If you want other lines then use \psline! – user2478 Dec 29 '18 at 16:16
• Yes, I see ah. :-) – Trong Vuong Dec 29 '18 at 16:28