[OSM-dev] [PATCH] Lowzoom: don't delete almost blue tiles

[Jeroen Dekkers]

Lowzoom has a check that it deletes a tile when the size is smaller
than 1000 bytes. The problem is that there are almost blue tiles like
http://osm-tah-cache.firefishy.com/~ojw/Tiles/tile.php/12/2102/1330.png
(only a very small piece of land in the lower right corner) that are
smaller than 1000 bytes. This results in the white squares that you
can currently see in the north of the Netherlands. Putting the check
at 500 byes should avoid the problem, because a fully blue tile is 571
bytes big. See the patch.

Jeroen Dekkers

Index: tools/lowzoom/lowzoom.pl
===================================================================
--- tools/lowzoom/lowzoom.pl	(revision 2675)
+++ tools/lowzoom/lowzoom.pl	(working copy)
@@ -90,7 +90,7 @@
   $Status->downloadCount($Layer,$X,$Y,$Z,$Size);
   
   # Don't bother storing blank or invalid tiles
-  unlink $f2 if($Size < 1000);
+  unlink $f2 if($Size < 500);
 }
 # Create a supertile, by merging together 4 local image files, and creating a new local file
 sub supertile(){