zonal statistics

[flo]

A zonal statistics plugin would be great. It would allow to extract raster statistics with a vector layer : mean raster value for each vector features (polygon, line or point), and also standard deviation, median...

[lutra]

meanwhile you have zonal statistics trough the GRASS plugin.

[flo]

Replying to lutra:

meanwhile you have zonal statistics trough the GRASS plugin.

Thank you for your answer, I use also Grass. However, I think it's an "usual" GIS task, and it would be more convenient if it could be directly done in Qgis, without Grass. Moreover, I think the zonal stat in Grass takes a lot of time to compute statistics (in comparison with Arcgis).

[borysiasty]

Could you please add this idea to ​http://www.qgis.org/wiki/Python_Plugin_Ideas ? We set that page over a year ago, so let's start using it! :)

[mhugent]

There is a zonal statistic function in the analysis library (analysis/vector/qgszonalstatistics.cpp/.h). I've wrote the function and a plugin because GRASS was too slow for my needs. However, also the function in the analysis lib is still far from optimal performance and follows a 'naive' approach. That's why I didn't commit the (GUI) plugin to trunk.

If you are interested in using the plugin, go to ​http://www.sourcepole.com/2010/12/16/zonal-statistics-plugin-for-qgis and download the source. It is explained on the page how to recompile.

Regards, Marco

[lutra]

Hi Marco, is really that bad? ;)

I would not mind to have even a sub optimal solution in QGIS and then have it upgraded when possible in the future...

[flo]

Thank you for this function. I've tested it and it seems to work fine ! Couldn't it be by default in Qgis ?