# tikz-3dplot: How can I recover the x,y,z components of a previously defined coordinate?

Specifically, in order to use the \tdplotsetcoord command to define coordinates and then use the \tdplotdefinepoints(Vx,Vy,Vz)(Ax,Ay,Az)(Bx,By,Bz) command that requires the x,y,z components of the three points to be known prior to calling the \tdplotdrawpolytopearc command to draw an arc between two vectors.

Can anyone help me fix my approach or demonstrate another method that works?

% drawing the axes
\draw[very thick,->] (0,0,0) -- (8,0,0) node[anchor=north east, very thick]{$y$ (West)};
\draw[very thick,->] (0,0,0) -- (0,8,0) node[anchor=north west, very thick]{$x$ (South)};
\draw[very thick,->] (0,0,0) -- (0,0,8) node[anchor=south, very thick]{$z$ (Zenith)};

% defining the origin
\coordinate (O) at (0,0,0);

% ploting sun vector and angles
\tdplotsetcoord{P}{8}{40}{60}
% draw a vector from origin to point (P)
\draw[-stealth,thick,color=red] (O) -- (P);

% plotting vector of the sky element
\tdplotsetcoord{Q}{8}{40}{-15}
% draw a vector from origin to point (Q)
\draw[-stealth,thick,color=blue] (O) -- (Q) node[thick,above] {se};

% plotting vector of the collector normal
\tdplotsetcoord{R}{8}{46}{115}
% draw a vector from origin to point (R)
\draw[-stealth,thick,color=nrkgreen] (O) -- (R) node[thick,above] {cn};

\tdplotdefinepoints(O)(P)(R) % problem in code is here!!!
\tdplotdrawpolytopearc[<->]{2}{anchor=north west}{$\theta$}