probably A would be slow because of the external call to gdalwarp On Wed, Jul 3, 2013 at 8:58 AM, Fred Lehodey <leho...@gmail.com> wrote:
> Hi, > I have no idea in terms of performance but I would bet on B option in your > case. > Thanks to give feedback. > > Regards. > > > On Wed, Jul 3, 2013 at 8:36 AM, Otto Dassau <das...@gbd-consult.de> wrote: > >> 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 > >
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