[Tex/LaTex] Question on drawing arcs

graphicstechnical-drawingtikz-3dplottikz-pgf

I have a very quick and easy question about the command \tdplotdrawarc.

Basically I have a code that shows spherical coordinates reference frame and the only thing I would like to do is to mark the angle with \theta as the complementary of the one it is marked right now.

The problem is that I tried to figure out how such command works but after several attempts I guess that something is not clear to me.

Can anyone help me with this simple stuff and let me have a better understand on how \tdplotdrawarc works in this case?

Thanks in advance 🙂

\documentclass{article} 

\usepackage{tikz}
\usepackage{tikz-3dplot}

\begin{document}
\tdplotsetmaincoords{60}{110}
%
\pgfmathsetmacro{\rvec}{.8}
\pgfmathsetmacro{\thetavec}{30}
\pgfmathsetmacro{\phivec}{60}
%
\begin{tikzpicture}[scale=5,tdplot_main_coords]
    \coordinate (O) at (0,0,0);
    \draw[thick,->] (0,0,0) -- (1,0,0) node[anchor=north east]{$x_{1}$};
    \draw[thick,->] (0,0,0) -- (0,1,0) node[anchor=north west]{$x_{2}$};
\draw[thick,->] (0,0,0) -- (0,0,1) node[anchor=south]{$x_{3}$};
    \tdplotsetcoord{P}{\rvec}{\thetavec}{\phivec}
    \draw[-stealth,color=red] (O) -- (P) node[above right]{$\bf{e_{\sigma}}$};
    \draw[dashed, color=red] (O) -- (Pxy);
    \draw[dashed, color=red] (P) -- (Pxy);
    \tdplotdrawarc{(O)}{0.2}{0}{\phivec}{anchor=north}{$\phi$}
    \tdplotsetthetaplanecoords{\phivec}
    \tdplotdrawarc[tdplot_rotated_coords]{(0,0,0)}{0.5}{0}%
        {\thetavec}{anchor=south west}{$\theta$}


\end{tikzpicture}
\end{document}

enter image description here

Best Answer

Do I get the question right ?

The package documentation reads : 

\tdplotdrawarc[coordinate system, draw styles]
    {center}{r}{angle start}{angle end}{label options}{label}

Could it be any clearer ?

The output

enter image description here

The code

\documentclass[12pt,tikz]{standalone}
\usepackage{tikz}
\usepackage{tikz-3dplot}

\begin{document}
\tdplotsetmaincoords{60}{110}
%
\pgfmathsetmacro{\rvec}{.8}
\pgfmathsetmacro{\thetavec}{30}
\pgfmathsetmacro{\phivec}{60}
%
\begin{tikzpicture}[scale=5,tdplot_main_coords]
    \coordinate (O) at (0,0,0);
    \begin{scope}[thick,->]
      \def\l{.8}
      \draw (O) -- (\l,0,0) node[pos=1.15]{$x_{1}$} ; 
      \draw (O) -- (0,\l,0) node[pos=1.1]{$x_{2}$} ; 
      \draw (O) -- (0,0,\l) node[pos=1.05]{$x_{3}$};
    \end{scope}
    \tdplotsetcoord{P}{\rvec}{\thetavec}{\phivec}
    \draw[-stealth,color=red] (O) -- (P) node[pos=1.1]{$\bf{e_{\sigma}}$};
    \tdplotdrawarc{(O)}{0.2}{0}{\phivec}{anchor=north}{$\phi$}
    \tdplotsetthetaplanecoords{\phivec}
    \tdplotdrawarc[tdplot_rotated_coords,blue]
        {(0,0,0)}{0.5}{\thetavec}{90}{anchor=south west}{$\theta$}

    \draw[dashed, color=red] (O) -- (Pxy) -- (P) ;
    \tdplotsetcoord{Pp}{.5}{90}{\phivec}
    \draw[blue!30] (Pxy) -- (Pp);
\end{tikzpicture}
\end{document}
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