[OSM-talk] tiles at home 404 handler, and assumed seas

Frederik Ramm frederik at remote.org
Tue May 15 11:29:14 BST 2007


Hi Joerg,

>> Meanwhile level-7 tiles were created that showed half of Europe under
>> water, which I found somewhat less than ideal. With no information on
>> whether the problem was known to OJW or whether he would want my help
>> in fixing it, and without write access to the relevant database, I
>> resorted to creating a list of those level-12 tiles that are "known
>> land" from Martijn's data, removing all existing tiles from the list,
>> and then uploading a 67-byte level-12 tile for the remaining tile
>> areas. I did all this for Europe only, resulting in the upload of
>> 250k tiles (don't worry, they are not stored on the server, each tile
>> upload is effectively only an INSERT to the empty-tile database with
>> 1000% overhead).
>
> What about creating a point in the middle of each tile which says  
> "this is
> land" and uploading it to the OSM-Main server. This way every  
> renderer could
> use this information and everyone can correct it in case it has  
> some minor
> bugs left.

This is a wholly different subject. You are talking about how to find  
out whether a tile is land or sea during the rendering stage. This is  
currently handled (for tiles at home) like this:

* if there is any coastline on the tile, draw the coastline and water  
on the right side (small bug here that Dutch reported recently, if  
coastline does not intersect the tile boundary it doesn't work  
properly, but we'll fix that)
* if there is no coastline, resort to the tile index file to  
determine wheter the background should be blue or white.

You are proposing a change to the second step, replacing the tile  
index file by control nodes. This is definitely a good idea for other  
large areas (woodland etc.) as soon as we upgrade close-areas.pl to  
handle those; I am not 100% convinced that it is a good idea for the  
land/sea thing because that would mean inserting at least 3 million  
extra nodes into the database.

The whole tiles at home extra database business, with 67-byte and 69- 
byte tiles and so on, is about how to deal with the information  
whether a tile is land or sea *after* this has been determined by the  
renderer; this is not affected by your suggestion.

Bye
Frederik

-- 
Frederik Ramm  ##  eMail frederik at remote.org  ##  N49°00.09' E008°23.33'






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