[gdal-dev] Projecting images with HTML5 Canvas in the web-browser

[Klokan Petr Přidal]

Hi everybody,

on Saturday during the Code Sprint of the FOSS4G 2009 conference in
Sydney we have made quite interesting step forward in the web
cartography.
With the help of other open-source developers I put together a
prototype of the client-side map reprojection implemented only in
JavaScript (using HTML5 Canvas tag and the Proj4js JavaScript
library).

An image as JPEG, PNG or GIF is with JavaScript in a web-browser
warped into a different map projection.
The example is reprojecting the world image into the Spherical
Mercator (map projection of Google Maps), into the map projection used
in US National Atlas, into Canada LCC and into the Mollweide
projection (used by National Geographic for thematic mapping).

To try it you need any web browser which supports HTML5, it means the
latest version of Firefox, Chrome, Safari or Opera.

Have a look at the demo:
http://examples.maptiler.org/map-reprojection-html5-canvas/

It is just a prove of concept in this moment, but I am sure practical
applications will follow.

The most typical use could be the client-side warping of raster data
(weather forecast, ..) into the correct image overlay of Google Maps
and similar online maps.
Any WMS sever providing only EPSG:4326 can now correctly overlay
Google Maps, if somebody use this technique to prepare the mash-up. Of
course the speed can be an issue in this moment, but there is plenty
of space for improvement in the warping code, and it can be done in a
separate computing thread, which is possible with HTML5 Web Workers...

Best,

Klokan Petr Pridal
-- 
http://blog.klokan.cz/
http://www.maptiler.org/
http://www.oldmapsonline.org/