[Tilesathome] Memory requirement of T at H

[Brent Easton]

Hi Maciek,

This is known as the T at H Unrenderability theorem:

For any given computer system, there exists a set of tiles that are too complex for that system to render in real time.

There are a couple of approaches to this problem:

1. I have working with Dodi on reducing the size of the SVG files generated. The files are bloated out with a lot of extra stuff that is outside of the render box and so never get's rendered. It get's pulled in along with the place names to handle generation of names accross tile borders. The use of the smart-linecaps feature for nearly every single line generated also blows out the size and complexity by a factor of at least 2, especially in the lowzoom processing. If we can reduce the size of the generated SVG, then Inkscape will be better able to process it. Dodi seems to be tied up at the moment, so this work has stalled.

2. I have added the option to use Batik instead of Inkscape to render tiles. You may have better luck with Batik in extreme situations. Unfortunately, there is a bug in Osmarender that causes Batik to fail occasionally. Still working on this one also.

3. A more general solution is to use Osmosis to cut the dowloaded OSM file into smaller strips for processing the higher zoom levels. This will result in smalled SVG's. Since the higher zoom levels process the SVG's in strips anyway, nothing is lost. This requires a mod to Osmosis and much work on tilesgen.pl and I just haven't had a chance to work on it.


Hopefully, after Christmas, we can get something happening. Options 1 and 2 are in hand. Any assistance offered with option 3 would be appreciated.


Regards,
Brent.



*********** REPLY SEPARATOR  ***********

On 19/12/2007 at 1:13 AM mkalkal  wrote:

>Hi,
>
>   My computer has 1GB of RAM and 3GB of swap,but  when I was given to 
>render such tiles :
>Doing tileset 1171,1547 (zoom 12)
>Doing tileset 2103,1347 (zoom 12)
>inkscape was  killed with out of memory message. My current system is 
>Debian lenny and i686 kernel.
>I wonder if I should to switch to amd64 kernel in order to give inkscape 
>more virtual space ?
>Simply adding more swap may not work.
>What do you think ?
>
>
>Maciek Kaliszewski
>
>
>
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____________________________________________________________
Brent Easton                       
Analyst/Programmer                               
University of Western Sydney                                   
Email: b.easton at uws.edu.au