[OSM-dev] Sea tiles to database

OJW streetmap at blibbleblobble.co.uk
Wed May 2 19:12:58 BST 2007


Unless there are any other suggestions, I propose:

1) database:
* creating a database of "all-sea" tiles
* populating it with the list of z-12 tiles
* deleting the images

That will save a few multiples of 1024 bytes (maybe 13,000,000 of?)

2) database access in 404 handler
* search on disk first for real tile
* if none found, use database to search for a sea tile
* if no sea-tile found, return white

3) optimise sea database
if someone has a workable idea for binary files to store the sea in, it can be 
exported regularly from the database into that format, to allow faster 
lookups while retaining the versatility of a database.

if not, we can still do things like
* merge 4 adjacent sea tiles into one at a 'lower' zoom level
* delete sea tiles whose parent is also sea (see hierachical database message)

As a first pass, this will only affect existing tiles.  The next step will be 
for upload handler to create sea tiles directly instead of storing them as 
images. (discussion for a different email thread maybe)

.  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  

To locate the z-12 sea tiles, I've extracted the data from today's 
oceantiles_12.dat file on svn[1].  I've generated an image[2] showing the 
results. These are the files that will get deleted, so shout if you can see 
any errors in the data or methods used to extract it (source code online[3])

[1] 
http://svn.openstreetmap.org/applications/rendering/tilesAtHome/oceantiles_12.dat
[2] http://dev.openstreetmap.org/~ojw/temp/seatiles.png
[3] http://dev.openstreetmap.org/~ojw/temp/


Regards,

OJW





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