The document discusses various web standards for data visualization, including SVG, WebGL, HTML, and 2D canvas. It outlines the strengths and weaknesses of each standard based on different visualization needs, such as complexity, interactivity, and the number of elements. The author shares practical examples of rendering mobility flow data for France using these technologies.

1. Exploring Web
Standards for Data
Visualization
Nicolas Garcia Belmonte
@philogb
Thursday, February 28, 13

2. Nicolas Garcia Belmonte
@philogb
Thursday, February 28, 13

3. Why so many standards
for Graphics?
SVG WebGL
HTML 2D Canvas
CSS JavaScript
Thursday, February 28, 13

4. What is the right standard
for my Visualization?
SVG WebGL
HTML 2D Canvas
CSS JavaScript
Thursday, February 28, 13

5. Political Engagement Map
Thursday, February 28, 13

6. Tweet Histogram Choropleth Map
Visual Component
# of Elements Small (~40) Small (~50)
Complex: (Concave, Convex,
Shape Complexity Simple: (Rectangle)
Connected, Disconnected)
Interactive Yes Yes
Standard Chosen HTML SVG
Thursday, February 28, 13

7. HTML / SVG
Good for a small # of simple-to-complex shaped
interactive elements
Thursday, February 28, 13

8. Mobility Flow in France
Per State and County Mobility Data for France
Thursday, February 28, 13

9. Thursday, February 28, 13

10. Mobility Flow in France
Per State and County Mobility Data for France
Visual Component Choropleth Map
# of Elements Medium/Big: ~40.000. US has only ~3.000.
Complex: (Concave, Convex, Connected,
Shape Complexity
Disconnected)
Interactive Yes
Standard Chosen ?
Thursday, February 28, 13

11. Mobility Flow in France
Take 1
SVG
Thursday, February 28, 13

12. Use SVG to render the Map
Thursday, February 28, 13

13. Failed Attempt
Thursday, February 28, 13

14. Mobility Flow in France
Take 2
2D Canvas / CSS3
Thursday, February 28, 13

15. Mobility Flow in France
Take 2 - 2D Canvas / CSS3
• Use Layered Images to render the Map
• Canvas Color Picking for Interaction
• CSS Transitions / Transforms for Zooming /
Panning
Thursday, February 28, 13

16. Mobility Flow in France
Canvas / CSS3
Thursday, February 28, 13

17. Mobility Flow in France
Images to render the Map
outline data picking
Thursday, February 28, 13

18. Mobility Flow in France
Canvas Color Picking for fast Interaction
Each State and County is assigned a unique (r, g, b, a) tuple.
We can encode up to 256^4 -1 data elements.
Thursday, February 28, 13

19. Canvas
An HTML Element
<canvas id='map' width='500' height='500'></canvas>
In which you can paste images
1 var canvas = document.querySelector('#map'),
2 ctx = canvas.getContext('2d'),
3 img = new Image();
4
5 img.src = 'map.jpg';
6 img.onload = function() {
7 ctx.drawImage(img, 0, 0);
8 };
And then retrieve it’s pixels
var pixelArray = ctx.getImageData(0, 0, width, height);
Thursday, February 28, 13

20. 2D Canvas Color Picking for fast Interaction
Offline: Encode index to county data array in colors
3 counties.forEach(function(county, i) {
4 var r = i % 256,
5 g = ((i / 256) >>> 0) % 256,
6 b = ((i / (256 * 256)) >>> 0) % 256;
7
8 county.setAttribute('fill', 'rgb(' + r + ',' + g + ',' + b + ')');
9 });
Online: Decode RGB color to array index
1 //decode index from image
2 function getCounty(canvas, counties, x, y) {
3 var imageData = canvas.getImageData(),
4 width = imageData.width,
5 data = imageData.data,
6 index = (x + y * width) * 4, //RGBA components
7 r = data[index],
8 g = data[index + 1],
9 b = data[index + 2],
10 i = r + (g + b * 256) * 256;
11
12 return counties[i];
13 }
Thursday, February 28, 13

21. CSS3 for Zooming
CSS transition definition
1 .maps {
2 transition: transform ease-out 500ms;
3 }
4
Set CSS transform via JavaScript
2 var style = map.style;
3 style.transform = 'translate(' + dx + 'px,' + dy + 'px) scale(' + s + ')';
Thursday, February 28, 13

22. Mobility Flow in France
CSS Transitions for Zooming
• Not good for synchronized / responsive animations
• GPU compositing messes up images when scaling
Thursday, February 28, 13

23. Almost had it...
Thursday, February 28, 13

24. Mobility Flow in France
WebGL
•Same image tile principle
•More control on animations
•More control on GPU management
Thursday, February 28, 13

25. WebGL
Thursday, February 28, 13

26. How does WebGL work?
...and why is it so fast?
JavaScript
WebGL JS API
GLSL API Vertex Shader
GLSL API Fragment Shader
Thursday, February 28, 13

27. How does WebGL work?
The 3D scene
image source: http://computer.yourdictionary.com/graphics
Thursday, February 28, 13

28. How does WebGL Scale?
Examples using PhiloGL
Thursday, February 28, 13

29. Thursday, February 28, 13

30. Data Facts
• 1200 weather stations
• 72 hours of data
• 5 variables - latitude, longitude, speed &
wind direction, temperature
= 460.000 items
Thursday, February 28, 13

31. Thursday, February 28, 13

32. Going 3D
Thursday, February 28, 13

33. //Create application
PhiloGL('canvasId', {
program: {
from: 'uris',
vs: 'shader.vs.glsl',
WebGL / PhiloGL
fs: 'shader.fs.glsl'
}, Rendering
camera: {
position: {
x: 0, y: 0, z: -50
}
},
textures: {
src: ['arroway.jpg', 'earth.jpg']
},
events: {
onDragMove: function(e) {
//do things...
},
onMouseWheel: function(e) {
//do things...
}
},
onError: function() {
alert("There was an error creating the app.");
},
onLoad: function(app) {
/* Do things here */
}
});
Thursday, February 28, 13

34. When choosing a Standard for
your Viz you could start by
asking yourself about...
# of Elements Small, Large
Shape Complexity Simple, Complex
Interaction Yes, No
Animation Yes, No
Compatibility Desktop, Mobile, Browsers, etc.
Libraries d3js, three.js, etc.
Thursday, February 28, 13

35. Thanks
@philogb
http://philogb.github.com/
Thursday, February 28, 13