[worldKit-dev] thoughts on an image tiling tool for <wms>

[Mikel Maron]

Following on from some discussion on Zoomifying large images and the like,
 I wrote up some thoughts on alternative schemes for worldKit.
 -Mikel
.....

worldKit supports a tiling scheme with the wms option. WMS is a method to request 
geographic imagery via a URL. You can request any arbitrary geographic extent with WMS.
The worldKit  option configures worldKit to query a WMS server, but with a predictable tiling scheme. 
 
The generic scheme is to start with a lowest resolution image covering the 
entire extent of the map (-180,-90,180,90 for a worldwide image), and then tile 
by powers of 2. So the second level of tiles requested cover extents 
(-180,0,0,90) (-180,-90,0,0) (0,0,180,90) (0,-90,180,0). The third level 
consists of 16 tiles, and so on. 
 
You can see an example of this at http://onearth.jpl.nasa.gov/ (follow the 
worldKit browser link) 
 
worldKit's request for imagery don't necessarily need to be received by an 
actual WMS server. My thought is that the preparsed image tiles can be named 
according to their extents and be requested as simple image file requests. 
 
So, what's missing is a way to take some imagery and break it up into tiles 
matching this scheme. This is what the Zoomify tool does well, however I don't 
think it's difficult to replicate. For instance, GSV 
[http://mike.teczno.com/giant/pan/]  is a similar tool written in python. This 
"PowersOfTwo" library would only need adjustment to the  naming scheme. 
 
(It would even be possible to post-process Zoomify-ied or PowersOfTwo images -- 
iterating over each image and translating the tile coordinate into geographic 
coordinates) 
 
Zoomify and GSV only apply to a single image. With multiple images, covering 
different extents, there are a couple of options. All the images could be 
composted into one large image, and then tiled. Or each image could be tiled 
seperately, and assigned to a seperate  option in worldKit. <wms> doesn't 
currently support a custom geographic extent, though that could be added easily.