## DEV Community # SVG, Geometry — and a dash of JavaScript

I'm currently reading Science Illustration — A History of Visual Knowledge from the 15th Century to Today. Highly recommended! Great books on science and/or design, are always a source of inspiration for me. The book is a treasure trove of great illustrations — and some of them are just meant to be coded in `<svg>`! ... like this one (sorry for the bad quality, picture taken with my phone): Luckily, it's not overly complex to do in `<svg>`.

We just need a bit of Math and JavaScript.

``````<svg viewBox="0 0 1000 1000"></svg>
``````

Now, we need some data!

The `viewBox` has a `size` of 1000, and we need 16 points around the circle:

``````const size = 1000;
const radius = size / 2;
const numOfPoints = 16;
``````

Next, let's create an array of points:

``````  const data = [...new Array(numOfPoints)].map((_a, index) => {
const angle = 360 / numOfPoints;
const radian = angle * (index + 1);
})
``````

We need a small helper-method, `polarToCartesian`, to get the coordinates of our 16 points:

``````const polarToCartesian = (r, degrees) => {
const radians = degrees * Math.PI / 180.0;
}
``````

A method like this typically needs `x` and `y` as well, but since these are the same as `radius` (in this case), we can go for a simpler version.

Cool, now we have an array of arrays:

``````[
[961.9397662556433, 691.3417161825449],
[853.5533905932738, 853.5533905932737],
...etc,
]
``````

For each point, we need to draw a line to all the other points, feeding in the `X` and `Y`of the current point:

``````const renderLines = (X,Y) => {
return data.map(entry => {
const [x,y] = entry;
if (X !== x && Y !== y) return `<line x1="\${X}" y1="\${Y}" x2="\${x}" y2="\${y}"></line>`
})
}
``````

Now, the only thing remaining is to call that method and set the returned string as `innerHTML` of our `<svg>`:

``````svg.innerHTML = data.map(entry => {
const [x,y] = entry;
return renderLines(x,y).join('');
})
``````

Let's see what we've built: Looks great, but a bit dull! Let's add a method for generating random values between a `min` and a `max`-range:

``````const random = (max, min = 0) => Math.floor(Math.random() * (max - min) + min);
``````

... and then use it to create random colors and stroke-widths:

``````const stroke = `hsl(\${random(360)}, \${random(100, 50)}%, \${random(90, 30)}%)`;
const strokeWidth = random(30, 3) / 10;
`````` Much better! Let's try to change the `numberOfPoints`-variable to a much lower value: Or perhaps a much higher value? Wow! Almost like a kaleidoscope. Or a rubber-ball!

## Demo

I hope this little post inspired you to do some creative things with `<svg>`.

Below is a Pen, where you can drag the "points"-slider to in- or decrease the number of points. Vincent A. Cicirello

Cool demo. If you want another category of graph to try something similar, you might take a look at generalized Petersen graphs. Could make another cool SVG demo. Here's a wikipedia page about them. Generalized Petersen graph

In graph theory, the generalized Petersen graphs are a family of cubic graphs formed by connecting the vertices of a regular polygon to the corresponding vertices of a star polygon. They include the Petersen graph and generalize one of the ways of constructing the Petersen graph. The generalized Petersen graph family was introduced in 1950 by H. S. M. Coxeter and was given its name in 1969 by Mark Watkins. Cool, thanks for sharing Karthik G Krishnan

OMG it's so cooooll!! 