[GIS] QGis Zonal Statistics Plugin NoData included in Calculations

pyqgispythonqgisstatisticszonal statistics

I have been trying to use the QGIS zonal statistics plugin. My raster has a nodata value of -99999 and all other values are positive. After computing the mean zonal statistics there are a number of features that have a negative mean indicating that the Zonal Stats plugin must be included nodata values in the calculations. Is there a workaround for this or am I doing something wrong:

from qgis.analysis import QgsZonalStatistics
vectorLayer = qgis.utils.iface.activeLayer()
rasterLayer = "path/to/my/raster/et_30.tif"
prefix = 'Test'
zoneStat = QgsZonalStatistics(vectorLayer, rasterLayer,prefix)
zoneStat.calculateStatistics(None)

Best Answer

It's not your fault. Here's the ticket for this issue: http://hub.qgis.org/issues/9349

Related Solutions

Zonal Statistics Tool for Median and Mode Raster Values

I haven't calculated mode values before (most frequently occurring value), but at least for quantile values you could try to use the plugin I coded (LecoS). Although not primarily intended for this use it is able to calculate some "zonal statistics" for polygon overlays.
How to:

Install numpy and scipy for your System and QGIS. On Windows choose the OSGEO4W advanced Install and select python-numpy and python-scipy. On Linux consult your linux package manager/compiler.
Download the experimental(!) LecoS plugin via the plugin downloader. The rest should be pretty self-explaining.

Please pay attention that the plugin is still experimental and calculation might fail sometimes! If you want a clear procedure suited for your needs than i would advise you to look into numpy and also R with the raster and sp packages. I am also happy to see detailed bug reports and i will do the best i can to fix them. However if the calculation fails for you, you better lookout for other tools as well.

[GIS] Automatisation of Zonal Statistics with python script

Soo I just found the solution for the 2)a) if someone once needs it, I added those lines :

from PyQt4.QtGui import *
from PyQt4.QtCore import *
from qgis.core import *
from qgis.utils import iface

Then it ran but nothing changed. After re-opening Python the column was created !!!

And one last thing : Be careful to Reload AND import again your script for each change (pretty heavy)

Best Answer

Related Solutions

Zonal Statistics Tool for Median and Mode Raster Values

[GIS] Automatisation of Zonal Statistics with python script

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