How to get mean of pixel values within a buffer zone around current mouse position in QGIS

Question

for a qgis 1.8 python plugin I want to query the mean of all pixel values of a raster layer within a defined buffer around the current mouse position, not for an existing point layer.

For the buffer sth like this should work:

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 all 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.
All I found is 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.

Answer 1

finally with some help from Anita I found following solution working for QGIS 1.8. Maybe useful for others:

import qgis.analysis
from PyQt4.QtGui import *

vpoly = QgsVectorLayer("Polygon", "pointbuffer", "memory")
feature = QgsFeature()
feature.setGeometry(QgsGeometry.fromPoint(QgsPoint(3517601,5406205)).buffer(10000,5))
provider = vpoly.dataProvider()
vpoly.startEditing()
provider.addFeatures( [feature] ) 
vpoly.commitChanges()
stats=qgis.analysis.QgsZonalStatistics(vpoly,"/path/to/corine2006_z0_test_gk3.tif")
stats.calculateStatistics(None)
allAttrs = provider.attributeIndexes()
provider.select(allAttrs)
provider.nextFeature(feature)
attrs = feature.attributeMap()
for (k,attr) in attrs.iteritems():
  if k==2:
    MessageBox.information(qgis.utils.iface.mainWindow(),'Info',attr.toString())

This is a solution for QGIS 2.0:

    vpoly = QgsVectorLayer("Polygon", "pointbuffer", "memory")
    feature = QgsFeature()
    feature.setGeometry(QgsGeometry.fromPoint(QgsPoint(3517601,5406205)).buffer(10000,5))
    provider = vpoly.dataProvider()
    provider.addFeatures( [feature] )
    vpoly.commitChanges()
    stats = qgis.analysis.QgsZonalStatistics(vpoly,"/path/to/corine2006_z0_test_gk3.tif")
    stats.calculateStatistics(None)
    allAttrs = provider.attributeIndexes()       
    for feature in vpoly.getFeatures():
        mean_value = feature.attributes()[2]
        MessageBox.information(qgis.utils.iface.mainWindow(),'Info',str(mean_value))