[postgis-users] PostGIS - server side optimization ( Split Data )

Markus Schaber schabios at logi-track.com
Thu Jan 13 05:51:23 PST 2005

Hi, Jordi,

On Wed, 12 Jan 2005 16:37:34 +0100
Jordi Ferran <jordi.ferran at gmail.com> wrote:

> Yes you're right, I misunderstand your comment. Using tables as
> "cache" for retrieving the "simplified" version instead of dynamically
> "simplify" it. You must take into consideration the cost:
> 1.- 650.000 geometries * 2 copies ( one simplified copy )

Depending on the zoom level, you do not have all copies in the table,
but only a few simplified ones. And in the detailed levels, you only
fetch a small part of the table.

> 2.- SQL select/update/delete, manage both tables simulatenously

Maintaining changes can be done with triggers or rules, but it slows
down this operations.

> 3.- the most important: you assume the simplify factor is fixed !

I'm shure he did not, you can use several simplified tables for
different zoom levels.

Then you can either "snap" your dynamic zoom level to the nearest
available level, or use the cache level that fits your dynamically best,
and have slightly suboptimal data.


markus schaber | dipl. informatiker
logi-track ag | rennweg 14-16 | ch 8001 zürich
phone +41-43-888 62 52 | fax +41-43-888 62 53
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