[OSM-dev] Tiles at home Strange sea rendering

[spaetz]

On Wed, Aug 08, 2007 at 03:01:29PM +1000, Brent Easton wrote:
> The tile is 12-3762-2471

There are two sources of "blankness" in osma. One is completely blank tiles (land/sea) without anything on them. I am currently deleting a lot of redundant information about that in the t at h server data base, so I thought it might have been my fault.

But if you look the meta info up: http://tah.dev.openstreetmap.org/Tiles/info.php?x=3762&y=2471&z=12&layer=tile
 you will see that there is a tile and that it has been uploaded recently by you. If a file is found the blank tile data base is never consulted, so I am not at fault here, pheww. :-)

> It is a landlocked tile with no coastline whatsoever (verified with JOSM search facility). It previously rendered perfectly, but today, suddenly starts rendering with a Sea background (both by myself and by other clients).

The second source of blankness comes from that oceantiles_12-png file, of which the latest version is here, I think: http://svn.openstreetmap.org/applications/rendering/tilesAtHome/tools/png2tileinfo/
 (revision history from here: http://trac.openstreetmap.org/browser/applications/rendering/tilesAtHome/tools/png2tileinfo)

I am no expert oh how that file works, but looking up pixel:x=3762+1 y=2471+1 (I *think* there is one pixel offset, because my app starts counting at 1 and tiles start at 0), your tile would be a white one, ie marked as containing costline. I don't know how the renderer treats that case. But I am not too sure about that, somebody else might know.
 
> Checking the doco indicates something about checking a list of sea tiles, of which an index is maintained by Kleptog. There seems to be no working link to actually check the status of a tile.

Load that ocenatile file and compare pixels :-)

spaetz

p.s. I was an am not involved in the oceantile business so don't ask me questions about how it works :-).
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