how to draw an arc using \coordinate-s?

[Goebel, Juergen, OPES27]

Hi,

the following example isn't working:

\documentclass{minimal}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
 \coordinate (W1) at (-5:3cm) {};
 \coordinate (W2) at (5:3cm) {};
 \draw (W1) arc (W2);
\end{tikzpicture}
\end{document}

Since the \draw-line doesn't follow the syntax that's not suprising.
But how can I achieve the wanted arc?

Regards,

Juergen

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[André Valentin-2]

Le 11 sept. 2009 à 15:04, Goebel, Juergen a écrit :

> Hi,
>
> the following example isn't working:
>
> \documentclass{minimal}
> \usepackage{tikz}
> \begin{document}
> \begin{tikzpicture}
>  \coordinate (W1) at (-5:3cm) {};
>  \coordinate (W2) at (5:3cm) {};
>  \draw (W1) arc (W2);
> \end{tikzpicture}
> \end{document}
>
> Since the \draw-line doesn't follow the syntax that's not suprising.
> But how can I achieve the wanted arc?

You must specify TWO angles:

  \draw (W1) arc (-5:5:3cm);




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[JL Diaz]

On Fri, Sep 11, 2009 at 3:04 PM, Goebel, Juergen
<juergen.goebel@...> wrote:
> \begin{tikzpicture}
>  \coordinate (W1) at (-5:3cm) {};
>  \coordinate (W2) at (5:3cm) {};
>  \draw (W1) arc (W2);
> \end{tikzpicture}
>
> Since the \draw-line doesn't follow the syntax that's not suprising.
> But how can I achieve the wanted arc?

Your wanted arc is not fully specified. You gave two points and want
an arc which pass through them, but.. what is the radius?

To specify an arc three points are needed (or two plus the center, or
two plus the radius, assuming negative radios mean the center at the
other side...)

Saludos,
--JL Diaz

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[Alain Matthes-2]

Le 11 sept. 2009 à 16:38, JL Diaz a écrit :

> On Fri, Sep 11, 2009 at 3:04 PM, Goebel, Juergen
> <juergen.goebel@...> wrote:
>> \begin{tikzpicture}
>> \coordinate (W1) at (-5:3cm) {};
>> \coordinate (W2) at (5:3cm) {};
>> \draw (W1) arc (W2);
>> \end{tikzpicture}
>>
>> Since the \draw-line doesn't follow the syntax that's not suprising.
>> But how can I achieve the wanted arc?

Hi

With O(0,0) I suppose you want the arc W1W2 with the center O.

The first solution is in the manual
\draw[red,thick] (W1) arc (-5:5:3 cm);

The second one is interesting but the angles
\AngleStart and \AngleEnd are not good : 355.08 and 4.91.
\tikzAngleOfLine is not correct perhaps the best solution would be
  to use fp.

\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{calc}

\newcommand{\tikzAngleOfLine}{\tikz@AngleOfLine}
\def\tikz@AngleOfLine(#1)(#2)#3{%
\pgfmathanglebetweenpoints{%
\pgfpointanchor{#1}{center}}{%
\pgfpointanchor{#2}{center}}
\pgfmathsetmacro{#3}{\pgfmathresult}%
}

\begin{document}
\begin{tikzpicture}
\draw[help lines] (0,0) grid (3,3);
  \coordinate (O) at (0 cm,0 cm);
  \coordinate (W1) at (-5:3cm);
  \coordinate (W2) at (5:3cm) ;
  \draw[red,thick] (W1) arc (-5:5:3 cm);
\end{tikzpicture}



\begin{tikzpicture}
\coordinate (O) at (0 cm,0 cm);
\coordinate (W1) at (-5:3cm);
\coordinate (W2) at (5:3cm) ;
\draw[->] (O)--(W1) (O)--(W2);
\tikzAngleOfLine(O)(W1){\AngleStart}
\tikzAngleOfLine(O)(W2){\AngleEnd}

\draw[red,thick] let \p1 = ($ (O) - (W1) $), \n2 = {veclen(\x1,\y1)}
    in   (W1) arc (\AngleStart-360:\AngleEnd:\n2);
\end{tikzpicture}
\end{document}

Best Regards

Alain Matthes
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[Flavio Costa]

The bottomline is that one CANNOT draw an arc using only coordinates, because the first parameter to arc operation is a coordinate but the second is not. I tried myself trying to automate some arc-drawing stuff, I could make it work by using the Math Engine and macros.

Flavio Costa



----- Mensagem original ----
De: Alain Matthes <alain.matthes@...>
Para: JL Diaz <jldiaz@...>
Cc: pgf-users@...
Enviadas: Sexta-feira, 11 de Setembro de 2009 13:03:53
Assunto: Re: [Pgf-users] how to draw an arc using \coordinate-s?

With O(0,0) I suppose you want the arc W1W2 with the center O.

The first solution is in the manual
\draw[red,thick] (W1) arc (-5:5:3 cm);

The second one is interesting but the angles
\AngleStart and \AngleEnd are not good : 355.08 and 4.91.
\tikzAngleOfLine is not correct perhaps the best solution would be
  to use fp.
...



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[Goebel, Juergen, OPES27]

Alain Matthes wrote:

> With O(0,0) I suppose you want the arc W1W2 with the center O.

Yes, you're absolutely right.  Sorry for the incomplete question.  

> The first solution is in the manual
> \draw[red,thick] (W1) arc (-5:5:3 cm);

ACK, but I'd like to use the two coordinates without repeating
the values.

> The second one is interesting but the angles
> \AngleStart and \AngleEnd are not good : 355.08 and 4.91.
> \tikzAngleOfLine is not correct perhaps the best solution would be
>   to use fp.

I'll have to see, if this is really necessary.

> \documentclass{minimal}
> \usepackage{tikz}
> \usetikzlibrary{calc}
>
> \newcommand{\tikzAngleOfLine}{\tikz@AngleOfLine}
> \def\tikz@AngleOfLine(#1)(#2)#3{%
> \pgfmathanglebetweenpoints{%
> \pgfpointanchor{#1}{center}}{%
> \pgfpointanchor{#2}{center}}
> \pgfmathsetmacro{#3}{\pgfmathresult}%
> }
>
> \begin{document}
> \begin{tikzpicture}
> \draw[help lines] (0,0) grid (3,3);
>   \coordinate (O) at (0 cm,0 cm);
>   \coordinate (W1) at (-5:3cm);
>   \coordinate (W2) at (5:3cm) ;
>   \draw[red,thick] (W1) arc (-5:5:3 cm);
> \end{tikzpicture}
>
>
>
> \begin{tikzpicture}
> \coordinate (O) at (0 cm,0 cm);
> \coordinate (W1) at (-5:3cm);
> \coordinate (W2) at (5:3cm) ;
> \draw[->] (O)--(W1) (O)--(W2);
> \tikzAngleOfLine(O)(W1){\AngleStart}
> \tikzAngleOfLine(O)(W2){\AngleEnd}
>
> \draw[red,thick] let \p1 = ($ (O) - (W1) $), \n2 = {veclen(\x1,\y1)}
>     in   (W1) arc (\AngleStart-360:\AngleEnd:\n2);
> \end{tikzpicture}
> \end{document}

Thanks a lot, that does the trick!

Juergen

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