Hi Fred, thanks for the hints, A and B sound interesting - PostGIS is not an option here.
One more question, because you already used these workarounds. What solution A or B should be more usable (faster) from your opinion, if I need to calculate the mean while moving the mouse over the map canvas? Regards Otto Am Tue, 2 Jul 2013 18:05:10 +0100 schrieb Fred Lehodey <leho...@gmail.com>: > Hi, > > Not sure it's the best way but I did something similar with these > workarounds: > > A - with gdal: > 1 - the user click and you get your buffer. (already done) > 2 - use gdalwarp with "-cutline" and "*-*crop_to_cutline" options to > extract a new raster. (python subprocess) > 3 - read the created raster in a numpy array to do all the statistics you > need. > > B - with matplotlib: > 1 - with the buffer: create an array of the vertices > 2 - read the raster into another numpy array > 3 - use the "points_inside_poly" function of "matplotlib" lib to create a > numpy mask. > > Not tried but postgis raster should do the job. > > Hth, > Fred > > > On Tue, Jul 2, 2013 at 1:12 PM, Otto Dassau <das...@gbd-consult.de> wrote: > > > Hi, > > > > for a qgis 1.8 plugin I would like to query the mean of pixel values of a > > raster layer within a defined buffer for the current mouse position (not > > for > > an existing point layer). > > > > For the buffer it works: > > > > ... > > feat.geometry().asPoint() > > (3.5176e+06,5.4062e+06) > > buff_geom = feat.geometry().buffer(1000, 5) > > buff_geom.asPolygon() [[(3.5186e+06,5.4062e+06), > > (3.51855e+06,5.4059e+06), (3.51841e+06,5.40562e+06), > > (3.51819e+06,5.4054e+06), (3.51791e+06,5.40525e+06), > > (3.5176e+06,5.4052e+06), (3.51729e+06,5.40525e+06), > > (3.51701e+06,5.4054e+06),...]] > > > > but now I try to find a solution to query the raster pixels within the > > buffer zone and calculate the mean, but I don't know how and if this is > > possible in QGIS 1.8 at all. I found QgsZonalStatistics, but that doesn't > > work for my task. > > > > Does anybody have a solution for this or a better idea, how to solve > > this? > > > > Thanks > > > > Otto > > _______________________________________________ > > Qgis-developer mailing list > > Qgis-developer@lists.osgeo.org > > http://lists.osgeo.org/mailman/listinfo/qgis-developer > > -- Geoinformatik Büro Dassau - http://www.gbd-consult.de FOSSGIS consulting , training , support and analysis Ackerstrasse 144c , D - 40233 Düsseldorf , Germany Tel: +49-(0)211-47468178 , Mobil: +49-(0)171-4687540 -- Community Advisor - QGIS Project Steering Committee _______________________________________________ Qgis-developer mailing list Qgis-developer@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-developer
