Overview
Super-Overlays are a form of KML in which data is broken up into regions. This allows Google Earth to refresh/request only particular sections of the map when the view area changes. Super overlays are used to efficiently publish large sets of imagery.
With super overlays, regions or tiles form a hierarchy. Each level of the hierarchy corresponds to a particular image resolution. Tiles that are lower in the hierarchy correspond to higher resolution. This allows Google Earth to progressively load higher resolution imagery as a user zooms in on the map.
GeoServer takes all the pain out of Super-Overlay creation, as it automatically creates the proper hierarchy and tiles the data. The only thing to be done is to add your data to GeoServer. It can tile vector data, but it truly shines with large raster data (GeoTiff, ArcGrid, GTOPO30, ImageFiles, and soon MrSID).
Consider the above tile which is at some level n of our hierarchy. As we zoom in we see higher resolution tiles for the next level n+1 are loaded.
Using Super Overlays
Getting GeoServer to return KML as a super overlay is easy. All one must do is append the parameter "superoverlay=true" to a KML request. For example:
http://localhost:8080/geoserver/wms/kml_reflect?layers=nurc:Img_Sample&superoverlay=true
In the current version we don't have a good 'lookAt' value, so Google Earth zooms you out. So you have to know where your layer is and zoom back in. In the future we hope to improve that.
Super Overlays and Tiling
GeoServer implements super overlays in a way that is compatible with the WMS Tiling Client Recommendation. Super overlays are generated in such a way that the regions of tiles of the super overlay are the same tiles that a WMS tiling client would request. The upshot of this is that one can use existing tile caching mechanisms and reap a potentially large performance benefit.
This tutorial walks through the process of setting up super overlays with tile caching.
 | Under Development Super overlays are still under active development. Please try it out and report any bugs in the issue tracker |
