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Mads Stoumann
Mads Stoumann

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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.

Science Illustration

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):

Interconnecting lines

Luckily, it's not overly complex to do in <svg>.

We just need a bit of Math and JavaScript.

To start with, we need a canvas:

<svg viewBox="0 0 1000 1000"></svg>
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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;
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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);
    return polarToCartesian(radius, radian)
  })
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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;
    return [r + (r * Math.cos(radians)), r + (r * Math.sin(radians))]
  }
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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,
]
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For each point, we need to draw a line to all the other points, feeding in the X and Yof 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>`
    })
  }
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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('');
  })
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Let's see what we've built:

BW Interconnecting Lines

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);
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... 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;
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Colour Interconnecting Lines

Much better! Let's try to change the numberOfPoints-variable to a much lower value:

Fewer points

Or perhaps a much higher value?

Many points

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.

Top comments (8)

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cicirello profile image
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.

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.

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madsstoumann profile image
Mads Stoumann

Cool, thanks for sharing

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devton_86 profile image
dev-ton

Awesome, inspiring article, for creative coders. :) thanks

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madsstoumann profile image
Mads Stoumann

Thanks!

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sergeyieffe profile image
Sergey Ieffe

Amusing book and nice math.

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kaarthikrishna profile image
Karthik G Krishnan

OMG it's so cooooll!!

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madsstoumann profile image
Mads Stoumann

Thank you!

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