How I can easily draw the direction cosines using TikZ?enter image description here

  • 1
    Welcome. What have you tried so far? Consider adding a minimal working example (MWE). – hola Aug 4 '14 at 2:38
  • I draw the vector but I don`t know how I can put the angles – alejandro muñoz Aug 4 '14 at 3:03
  • \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]{$x$}; \draw[thick,->] (0,0,0) -- (0,1,0) node[anchor=north west]{$y$}; \draw[thick,->] (0,0,0) -- (0,0,1) node[anchor=south]{$z$}; \tdplotsetcoord{P}{\rvec}{\thetavec}{\phivec} \draw[-stealth,color=red] (O) -- (P) node[above right] {$P$}; \end{tikzpicture} – alejandro muñoz Aug 4 '14 at 3:05
  • @alejandromuñoz Have a look at the example in chapter 3.5.1 tdplotdrawarc in the tikz-3dplotdocumentation – Dan H. Aug 4 '14 at 6:45

This is a 3D solution via tikz-3dplot. Two inputs are required (1) Euclidean coordinate (\ax,\ay,\az) and (2) its Euclidean 2-norm/distance \r.

The code below basically does the following

  1. Draw coordinate systems
  2. From input, one gets the P point, then extended to V point via external extention skill.
  3. Draw angles from P to 3 axes in the first quadrant, respectively via tdplot-define-points command which requires 3 inputs (the origin, P, and a point in axis) to form a triangular polytope
    and then draw the each arc via tdplot-polytope-arc.

enter image description here



%  ---- draw coordinates
\def\r{0.7}               %{0.655} %  2-norm of (x,y,z)
\coordinate (O) at (0,0,0);  

(0,0,0) -- (1.3,0,0)node[anchor=north east]{$\mathbf{V_x}$};   
\draw[thick,->,orange] (0,0,0) -- (0,1.3,0)node[anchor=north west]{$\mathbf{V_y}$}; 
\draw[thick,->,orange] (0,0,0) -- (0,0,1.3)node[anchor=south]{$\mathbf{V_z}$};

(0,0,0) -- (1,0,0)node[above]{$\mathbf{e_x}$}; 
\draw[thick,->,blue]  (0,0,0) -- (0,1,0)node[below]{$\mathbf{e_y}$}; 
\draw[thick,->,blue]  (0,0,0) -- (0,0,1)node[right]{$\mathbf{e_z}$};   
% ---- start from P to draw angles a, b, c
\coordinate [] (P) at (\ax,\ay,\az){}; 
\draw[-stealth,thick] (P) -- ($(P)!-0.3cm!(O)$) coordinate (V)node[above]{$V$};

{     %define 3 points 0,A,B for angle c
\draw[fill=cyan](0,0,\r) --(0,0,0)--(\tdplotbx,\tdplotby,\tdplotbz);
\tdplotdrawpolytopearc[vector]{\r}{anchor=south}{$c$}     % draw arc arrow
{     %define 3 points 0,A,B for angle a
\tdplotdrawpolytopearc[vector]{\r}{anchor=south}{$a$}     % draw arc arrow
{     % define 3 points 0,A,B for angle b
\draw[fill=cyan](0,\r,0) --(0,0,0)--(\tdplotbx,\tdplotby,\tdplotbz);
\tdplotdrawpolytopearc[vector]{\r}{anchor=west}{$b$}      % draw arc arrow
| improve this answer | |

A simple 2-D solution:

\definecolor{corange}{rgb}{0.93, 0.57, 0.13}
\begin{tikzpicture}[>=latex,scale=0.7,inner sep=2pt]
\path coordinate (o) at (0,0)
coordinate (x) at (220:4)node(X) at($(o)!.9!(x)$)[label=below right:$\textcolor{corange}{V_x}\textcolor{blue}{e_x}$]{}
coordinate (y) at (0:6) node(Y)  at($(o)!.9!(y)$)[label=below:$\textcolor{corange}{V_y}\textcolor{blue}{e_y}$]{}
coordinate (z) at (90:6)node(Z)  at($(o)!.9!(z)$)[label=right:$\textcolor{corange}{V_z}\textcolor{blue}{e_z}$]{}
coordinate (v) at (50:5)node at($(o)!1!(v)$)[label=right:$V$]{};

\draw [fill=green,->]($(o)!.42!(y)$)to (o) to($(o)!0.5!(v)$) to [bend left] node[right]{$b$}($(o)!.42!(y)$);
\draw [fill=green,->]($(o)!.37!(z)$)to (o) to($(o)!0.4!(v)$) to [bend right] node[above]{$c$}($(o)!.37!(z)$);
\draw [fill=green,->]($(o)!.3!(x)$)to (o) to($(o)!0.25!(v)$) to [bend right] node[above left]{$a$}($(o)!.3!(x)$);
\draw  (o) edge [->,corange] (x) edge [->,thick,blue] (X)
           edge [->,corange] (y) edge [->,thick,blue] (Y)
           edge [->,corange] (z) edge [->,thick,blue] (Z)
           edge [->,thick] (v); 

The result is like this:

enter image description here

| improve this answer | |

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