[Tilecache] TileCache, a fast Tile Server

[Paul Spencer]

Note that mapserver no longer has a hard limit on the size of the  
image compiled.  The default size is 2048x2048, but you can override  
this in your mapfile using:

MAXSIZE [integer]
Sets the maximum size of the map image. This will override the  
default value. For example, setting this to 2048 means that you can  
have up to 2048 pixels in both dimensions (i.e. max of 2048x2048).

We have experimented with rendering meta tiles up to 24 x 24  
(6144x6144 pixels) with good success.  In general, rendering larger  
meta tiles takes longer, but the overall tiles/sec increases ...  
which was a little counter-intuitive to me, I assumed that it would  
actually start to get worse at some point.  But thinking about it, it  
does make sense that mapserver has somewhat less work to do because  
it can draw more with the same set of brushes, so the overhead of  
initialization of the individual renders becomes less of a factor.

I'm not sure if there is an upper limit on this, we stopped at 24x24  
because it was convenient to do so.  Also this assumes you are pre- 
rendering, not building the cache on the fly.  If you are building  
the cache on the fly, it becomes unacceptable to wait for such a  
large map draw for one tile request.

Cheers

Paul


On 29-Aug-07, at 8:36 PM, Christopher Schmidt wrote:

> Note that the default is 5,5 tiles per metatile. This is  
> configurable. However,
> MapServer has a compiled in limit of image size of 2048 x 2048, which
> means that hte maximum number of 256px square tiles is 7x7 (including
> the metaBuffer pushes it over the limit at 8x8). If you change the  
> limit
> in MapServer, I have heard reports that the performance for pre- 
> caching
> is great (though this was reported with ka-Map, rather than with
> TileCache specifically). In general, the bigger of an image you can
> provide, the less overlabelling you will see (due to shared  
> polygons and
> the like), and you'll get higher overall performance: 4 small 256x256
> image renders takes approximately 3 times as long as one big 512x512
> render in many simple rendering situations. (Of course, all of this is
> dependant on your specific data and cartographic rules.)

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|Paul Spencer                          pspencer at dmsolutions.ca    |
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|Chief Technology Officer                                         |
|DM Solutions Group Inc                http://www.dmsolutions.ca/ |
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