Wednesday, December 31, 2008

OpenLayers and Djatoka

For the last few weeks, I've been playing around with the new JPEG2000 image server released by the Los Alamos National Labs ( I never could get the image viewer released along with it to work, and I immediately thought of OpenLayers (, a javascript API for embedding maps. OpenLayers is like Google Maps in many ways, but Free. Besides maps, it works very well for any image, and provides a lot of tools developed for mapping, but also useful for displaying and working with any large image. I wanted to use OpenLayers support for tiled images in conjunction with Djatoka's ability to render arbitrary sections of an image at a number of zoom levels (the number of levels available depends on how the image was compressed).

After a lot of messing around and some false starts, I've developed a Javascript class that supports Djatoka's OpenURL API. I've been testing it on JPEG2000 images created with ContentDM in the UNC Library's digital collections, with a good deal of success. The results are not yet available online, because I don't have a public-facing server I can host it on, but the source code is up on github here.


Install Djatoka. Incidentally, in order to get this in the queue for installation on our systems, I had to make Djatoka work on Tomcat 6. The binary doesn't work out of the box, but when I rebuilt it on my system (RHEL 5), it worked fine.

Copy the adore-djatoka WAR into your Tomcat webapps directory. Follow the instructions on the Djatoka site to start the webapp.

Grab a copy of OpenLayers. Put the OpenURL.js file in lib/OpenLayers/Layer/ and run the script.

To just run the demo, copy the djatoka.html, the OpenLayers.js you just built, and the .css files from OpenLayers/theme/ and from the examples/ directory, as well as the OpenLayers control images from OpenLayers/img into the adore-djatoka directory in webapps. You should then be able to access the djatoka.html file and see the demo.

This all comes with no guarantees, of course. It seems to work quite well with the JPEG2000 images I've tested, and the tiling means that each request of Djatoka consumes an equal amount of resources. I've run into OutOfMemoryErrors when requesting full-size images, but this method loads them without any problem.

Update (2009-01-05 14:37): I've posted a fix to the OpenURL.js script for a bug pointed out to me by John Fereira on the djatoka-devel list. If you grabbed a copy before now, you should update.

Update: screenshots --