Mapnik renderer fallback to OSM when network available

[GoogleCodeExporter]

I just had a thought that it might be possible to combine the OSM and mapnik 
renderers so that when it's possible to contact a tile server any zoom levels 
not preprocessed by mapnik become available from OSM. Perhaps it is possible to 
display the mapnik preprocessed tile of best fit then overlay it with the OSM 
downloaded tile when it is downloaded, effectively using the mapnik instead of 
the default grey background that is displayed until a tile downloads?

This might be rendered irrelevant if a vector renderer is implemented of course.

Also without looking at the specifics of the storage format, perhaps it's 
possible to over time allow storing any tiles downloaded in the same format as 
the mapnik preprocess step?

Original issue reported on code.google.com by mark%het...@gtempaccount.com on 20 Oct 2010 at 11:36

[GoogleCodeExporter]

Seems like a nice idea. My thoughts about this:

 * The downloaded tiles could be saved in the MapnikRenderer format, slowly filling the files. Loading tiles from a gradually filled file would be slower, though, as adjacent tiles are not necessarily adjacent in the file any more. The format would still require the index file to be initialized properly. Once a tile is written to the file it cannot be changed anymore.
 * Tiles from lower zoom levels could be upscaled until a replacement has been downloaded
 * It must be possible to switch off downloading tiles ( e.g. to avoid roaming coasts on a mobile device )
 * One problem I foresee is that accumulating tiles slowly could lead to inconsistencies in the displayed map.
 * A preprocessor plugin without Mapnik as a dependency should still be available as Mapnik is not easy to get / compile ( many dependencies ).

Original comment by veaac.fd...@gmail.com on 21 Oct 2010 at 12:32

• Changed state: Accepted
• Added labels: Type-Enhancement
• Removed labels: Type-Defect