[GRASS-user] Searching for technical details on how v.rast.stats calculates means and other statistics

[RichardCooper]

Hi,

I'm trying to determine the specifics of how v.rast.stats calculates means
and other statistics, for which I have a couple of queries. 

I apologise in advance if this information exists online, but I couldn't
find all the details in module guidelines or related documents and scripts.

I understand that v.rast.stats uses v.to.rast and r.univar for determining
means and statistics.

Qu. 1. Raster cells are only created (by v.to.rast) if their centre point is
within the area boundary ?
I'm using a vector area layer, and my observation after rasterizing, is that
this is the case, and cells are not created if their centre point lies
outside the area boundary.

Qu. 2. If a single cell representing a unique category in the zones layer
(generated previously by v.to.rast) overlays four cells in the input raster,
how is the mean calculated. Is it a simple sum of the four cell values
divided by n number of cells (four in this case), or is the value weighted
in some way? Not being a expert programmer, I can't really tell from the
r.univar script, and it doesn't appear from my observation to be a simple
mean calculation.

Many thanks for your comments,

Richard


GRASS version: 7.0.0svn                                                         
GRASS SVN Revision: 64042                                                       
Build Date: 2015-01-10                                                          
Build Platform: i686-pc-linux-gnu                                               
GDAL/OGR: 1.11.1                                                                
PROJ.4: 4.9.0                                                                   
GEOS: 3.4.2                                                                     
SQLite: 3.7.9                                                                   
Python: 2.7.3                                                                   
wxPython: 2.8.12.1                                                              
Platform: Linux-3.2.0-31-generic-pae-i686-with-LinuxMint-13-maya                



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