Tiling

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This page belongs to the tiling mailinglist which has been initiated after the Foss4g 2010 BoF on tiling. At the BoF it became clear that there is a need for more advanced cache management in the various tile-cache programs.

Problems

  • Tiling produces too many files to handle
  • There is need for usage-statistics on tiles
  • A smarter way for seeding is needed
  • A smarter way for deleting tiles is needed
  • GetFeatureInfo is needed (mainly bypass the requst to the backend)

Possible solutions

GeoWebCache uses a paging algorithm to manage the statistics of the tiles. Tiles are grouped in page-files and the deeper the zoomlevel the more files are in the page file. Usage statistics are handled at the page-file level, not per tile.

OSM uses special PNG files where 8x8 tiles are grouped with a special header to locate the individual tiles. This way the number of files are reduced. It is not clear of 8x8 is optimal.

Empty/single color tiles should be recognised and linked to one file. Mapproxy uses a color lookup algorithm to check if there is only one color per tile.

Use polygons as input for tileseeding.

To optimise I/O on the mapserver, use depth traversing tileseeding.