[Qgis-developer] Approximate reprojection for vectors

[Marco Hugentobler]

Hi Martin

> btw. the feature cache from #3200 is based on R-tree.

Wow, cool!
One question to the feature cache patch (didn't yet look into the code in 
detail, so maybe a silly one):

Reading the usage notes of the QgsFeatureCache class, it seems to me the 
implemented strategies are optimised for desktop scenario where user loads a 
scene and then zooms in.
In a wms server scenario, it would be nice to cache features in the tiles most 
viewed by visitors (e.g. parts of the city rather than countryside), but the 
zoom-in scenario is less likely in a webgis. Is the code in the patch  already 
optimised for the web-scenario or is it necessary to implement a new 
mode/strategy?

Regards,
Marco



+ * Last currently implemented mode/strategy is called "heuristics". This 
strategy
+ * compares the currently cached region with the requested one - and in case 
its
+ * much bigger, the cached area is downsized to free it's (probably) unused 
parts.
+ * This heuristics is based on the idea that user mostly starts editing with 
a big
+ * map and he zooms-in afterwards, editing only a small part of the whole 
map.
+ * This means he mostly doesn't need all the data in memory...

Am Dienstag, 1. November 2011, 14.50:20 schrieb Martin Dobias:
> On Tue, Nov 1, 2011 at 9:38 AM, Marco Hugentobler
> 
> <marco.hugentobler at sourcepole.ch> wrote:
> >> > Martin I just found that you proposed a patch to allow speed up vector
> >> > rendering
> >> > 
> >> > http://hub.qgis.org/issues/3200
> >> > 
> >> > maybe this can be tested again and added in time for 1.8?
> >> 
> >> Giovanni,
> >> porting and testing the patch would need quite a lot of time.
> >> Definitely not something that could be released soon.
> > 
> > A propos feature caching: there was an interesting presentation at foss4g
> > 2007 about feature caching:
> > 
> > http://2007.foss4g.org/presentations/viewattachment.php?attachment_id=131
> > 
> > The idea to use r-Tree entities as data blocks sounds reasonable. Would
> > be cool to have something like this in QGIS.
> 
> Hi Marco
> 
> btw. the feature cache from #3200 is based on R-tree.
> 
> Martin


-- 
Dr. Marco Hugentobler
Sourcepole -  Linux & Open Source Solutions
Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
Technical Advisor QGIS Project Steering Committee