TikZ Challenge 1 - Geometrical Diagram

[I like Serena]

Who can make the most impressive, interesting, or pretty TikZ picture?

This first challenge is to create a geometrical diagram, like a triangle, that is somehow interesting or impressive.
We might make it a very complicated figure, or an 'impossible' figure, or use pretty TikZ embellishments, or use 'neat' $\LaTeX$ features, or... well... that's up to you!
If it's not immediately obvious, please mention what makes your picture special.

Please post your submission in this thread.
This thread will be closed after 2 weeks.
After that we will have 2 weeks to vote on what we think is the 'best' or 'prettiest' TikZ picture.

Only 1 submission of a picture is allowed, and it is not allowed to change the picture after submission.
It is allowed to add more information later to clarify what makes the picture special.
Any change to the picture itself will disqualify it.
See http://mathhelpboards.com/tikz-pictures-63/tikz-announcement-22140.html for more information on how to create and post TikZ pictures.
To help create pictures we can use this http://35.164.211.156/tikz/tikzlive.html.

 

[I like Serena]

To start things off, here is my submission:
\begin{tikzpicture}[blue]
\coordinate (A) at (0,0);
\coordinate (B) at (4,0);
\coordinate (C) at (4,3);
\draw[blue, ultra thick] (A) -- (B) -- (C) -- cycle;
\path (A) node[below left] {A} -- (B) node[below right] {B} -- (C) node[above] {C};
\path (A) -- node[below] {c} (B) -- node

{a} (C) -- node[above left] {b} (A);
\path (A) node[above right, xshift=12] {$\alpha$};
\draw[thick] (B) rectangle +(-0.4,0.4);
\draw[thick] (A) +(1,0) arc (0:atan(3/4):1);
\end{tikzpicture}

This picture is special because it's a basic shape that showcases:

1. Naming coordinates.
2. Drawing a closed polygon.
3. Embellishing with properties (for color and thickness).
4. Adding labels next to nodes and next to lines.
5. Specifying relative coordinates.
6. Drawing an arc.
7. Using a mathematical function (for the angle of the arc).

 

[Greg]

\begin{tikzpicture}[scale=2]
\usetikzlibrary{calc}
\coordinate (A) at (0,0);
\coordinate (B) at (1,2.5);
\coordinate (C) at (4,0);
\draw (A) -- (B) -- (C) -- cycle;
\draw (B) -- ($(A)!(B)!(C)$) ++(90:0.2) -- ++(0:0.2) -- +(-90:0.2);
\draw (A) -- ($(B)!(A)!(C)$) ++(-39.806:0.2) -- ++(50.194:-0.2) -- +(-39.806:-0.2);
\draw (C) -- ($(A)!(C)!(B)$) ++(68.2:-0.2) -- ++(-21.8:0.2) -- +(68.2:0.2);
\draw (A) node

{$A$} -- (B) node[above]{$B$}node[midway,above]{$c\quad$} -- (C)node

{$C$}node[midway,above]{$\quad a$} -- (A)node[midway,below]{$b$};
\node[align=center,font=\bfseries, yshift=2em] (title)
at (current bounding box.north)
{An illustration of the altitudes of a triangle, \\ intersecting at a single point called the orthocenter};
\end{tikzpicture}

This TikZ diagram includes a title.​

 

[MarkFL]

\begin{tikzpicture}
\draw[<->][red] (-5.5,0) -- (5.5,0) node

{$x$};
\draw[<->][red] (0,-5.5) -- (0,5.5) node[above] {$y$};
\foreach \x in {-5,-4.5,...,-0.5,0.5,1,...,5}
{
\foreach \y in {-5,-4.5,...,-0.5,0.5,1,...,5}
{
\def \angle {atan((3*\x*\y)/(2*(\x)^2-(\y)^2))};
\draw[thick,blue] ({\x + 0.1*cos(\angle)},{\y + 0.1*sin(\angle)}) -- ({\x + 0.1*cos(\angle + 180)},{\y + 0.1*sin(\angle + 180)});
}
}
\end{tikzpicture}

This TikZ diagram illustrates a direction field for a magnetic dipole, and utilizes the following:

• Nodes for the axis labels.
• Nested foreach loops.
• The definition of an angle (slope) based on coordinates.
• Parametric values for the endpoints of line segments.

 

[lfdahl]

[TIKZ][scale=3]
\draw[step=.5cm, gray, very thin] (-1.2,-1.2) grid (1.2,1.2);
\filldraw[fill=green!20,draw=green!50!black] (0,0) -- (3mm,0mm) arc (0:30:3mm) -- cycle;
\draw[->] (-1.25,0) -- (1.25,0) coordinate (x axis);
\draw[->] (0,-1.25) -- (0,1.25) coordinate (y axis);
\draw (0,0) circle (1cm);
\draw[very thick,red] (30:1cm) -- node[left,fill=white] {$\sin \alpha$} (30:1cm |- x axis);
\draw[very thick,blue] (30:1cm |- x axis) -- node[below=2pt,fill=white] {$\cos \alpha$} (0,0);
\draw (0,0) -- (30:1cm);
\foreach \x/\xtext in {-1, -0.5/-\frac{1}{2}, 1}
\draw (\x cm,1pt) -- (\x cm,-1pt) node[anchor=north,fill=white] {$\xtext$};
\foreach \y/\ytext in {-1, -0.5/-\frac{1}{2}, 0.5/\frac{1}{2}, 1}
\draw (1pt,\y cm) -- (-1pt,\y cm) node[anchor=east,fill=white] {$\ytext$};
[/TIKZ]

This TikZ picture is special, because it demonstrates:
- The very foundation of trigonometry
- Construction of a coordinate system
- Construction of a grid
- Coloring of line segments
- The making of tick labels
- How to fill in with colors
- How to use different line thickness
- How to position labels

 

[I like Serena]

Thank you everyone for your submissions!

I've created a http://mathhelpboards.com/challenge-questions-puzzles-28/tikz-challenge-1-voting-22273.html, which will be open for 2 weeks.
Please everyone, give your vote!

Closing this thread.