How can I use LaTex to mark my delta y and my delta x?

Question

I know it is possible to use curly brackets (braces) in both vertical and horizontal orientation in Latex. Can I somehow use this to mark my change in y and my change in x on a Coordinate plane?

Here's an image of what I am trying to accomplish.

This graphic is produced in Geogebra 4.2 and as you can see it's a very simple idea. But I had to use the pen tool to draw the curly bracket and I used Latex to typeset the delta y and delta x. Why not use Latex for both of these?

Here's another image where I actually used Latex commands \rbrace and \underbrace to produce the brackets.

It worked out pretty good in this case. But had the slope of this line been bigger and I wanted to mark a larger distance the bracket would not be long (or high) enough. What I have done with these two is I have increased it's "size" to make it bigger. But this results in a much thicker lines. Can I control the width and length of the bracket by some argument?

What is the syntax and what are the possible arguments for the \underbrace command? Is there any official resource page where I can look this up? Like a command catalog?

Answer 1

You can use decoration={brace, amplitude=5pt} from decorations.pathreplacing library of tikz.

\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.pathreplacing}
\begin{document}
\begin{tikzpicture}
\draw[dashed, thin,gray!50] (0,0) grid (12,12);
\draw[very thick, -latex](-1,0) -- (12,0);
\draw[very thick, -latex](0,-1) -- (0,12);
\draw[thick, ](0,0) -- (11,9);
\draw[very thick, ](8.5,6.95) -- (8.5,3);
\draw[very thick,rotate=0,decorate, decoration={brace, amplitude=5pt}] (8.7,6.95)--(8.7,3);  %%%  <----Puts the vertical brace
\draw[very thick, ](8.5,3) -- (3.7,3);
\draw[very thick,rotate=0,decorate, decoration={brace, amplitude=5pt}] (8.5,2.8) -- (3.7,2.8);  %%% Puts the horizontal brace.
\node at (9.4,5) {\Large $\Delta y$};
\node at (6.1,2.36) {\Large $\Delta x$};

\node at (3.5,3.2) {\Large A};
\node at (8.4,7.25) {\Large B};
\node at (8.7,2.7) {\Large C};

\foreach \x in {1,2,...,11} { \draw[thick] (\x,0) -- (\x,-0.2); }
\foreach \y in {1,2,...,11} { \draw[thick] (0,\y) -- (-0.2,\y); }

\foreach \x in {1,2,...,11} { \node [anchor=north] at (\x,-0.3) {\x}; }
\foreach \y in {1,2,...,11} { \node [anchor=east] at (-0.3,\y) {\y}; }
\node at (-0.5,-0.5) {0};

\end{tikzpicture}

\end{document}

For more details type: texdoc pgfmanual from command prompt, or goto www.texdoc.net and search for pgfmanual. You can draw your graph entirely with tikz and/orpgfplots. If you find it difficult, draw the graph in geogebra, export it as tikz code and use the lines that produce the braces with appropriate co-ordinates (The lines are pointed to by comments in code).

Answer 2

You could use TikZ for this thing. Position your image inside a tikzpicture environment like so:

\documentclass{standalone}
\usepackage{tikz}
\usepackage[demo]{graphicx} % Do not use demo in your code!!!

\begin{document}
\begin{tikzpicture}
    \node (pic) at (0,0) {\includegraphics{test.pdf}};
    \coordinate (A) at (3,4); % Play arround to get the coordinates by hand
    \coordinate (B) at (8,4);
    \coordinate (C) at (8,8);
    % Use the code from the Question mentioned bellow and use the defined coordinates
\end{tikzpicture}
\end{document}

Then use the tip described in Draw Curly Braces in TikZ.

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You could also use pgfplots and then position the nodes at some specific (x,y) coordinates and this would help you avoid manual fidling when searching for proper A, B and C coordinates.

There are some answers related to node positioning in PGF plots here:

• Label plots in pgfplots without entering coordinates manually
• pgfplots: Placing node on a specific x-position

The pgfplots manual can be found here.