[webmap-discuss] OGC and google style tiling

Stephen Woodbridge woodbri at swoodbridge.com
Thu Apr 27 10:22:53 EDT 2006

Steven M. Ottens wrote:
> Paul Spencer wrote:
>>there are a couple of very good reasons for this (in my opinion).  The
>>approach you suggest is actually the first one I tried because I was
>>focussing on the client side code at the time.  It became obvious that
>>it would not actually work in a real world situation because:
>>1) every request to mapserv starts the CGI, loads the map, renders the
>>map and returns it.  This takes a substantial amount of time, even if
>>your map file and data are highly optimized.  For instance, my test
>>cases would take about 1-2 seconds per tile, with a HUGE load on the
> The idea is to get serverside cache, we have caching working on
> mapserver.cgi requests, which means it can can deliver lots and lots of
> tiles in a second. The reason I'm developing tiling is because our
> current setup can only handle 20 concurrent users and we need 300. If we
> can server from cache we can do that, and tiling is a way to make sure
> identical images are served to users and as such can be served from cache.
> Also in your situation you need to run a tile.php, a mapserver.cgi and a
> gd (why btw?) image process. If you multiply this 300 times it's also
> quite a load on the server. I prefer to keep as much load on the client
> side as possible.


You mentioned that you can use apache to handle caching of mapserver 
CGI, so this could also be done for tile.php.

Also I would consider, you mod_rewrite to convert the tile.php request 
into a direct file hit first and only if the file does not exist, then 
call tile.php to generate. This would significantly improve performance. 
There are also tools with ka-map to pre generate all the tiles into the 
tile cache.

-Steve W

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