[gdal-dev] Zonal Grid Statistics

[Nicolas Cadieux]

Hi,

I am currently using the SAGA Zonal Grid Statistics found here: 
http://www.saga-gis.org/saga_tool_doc/7.0.0/statistics_grid_5.html (both 
Zonal and Continuous Data are Rasters with the same extent and pixel 
posting). It works well but SAGA load both grids into memory.  Since my 
grids are the size of Canada , I am running out of memory.  Zones are 
land cover type but can also be Aspect and Slope (in 5 degree 
implements).  My continuous data (my grid to analyse) are basically DEM 
height errors.  So the general idea is to get the min, max, mean... 
error by land cover type (or slope Aspect...)

Is there a GDAL utility that can do this (with two raster files) without 
loading the raster into memory?

If not, is there a python code that you know of can help me calculate 
MIN MAX MEAN STDEV SUM by Zone.

If not, I was thinking the best way to do this would be to read both 
rasters one pixel at a time and then to make a python dictionary 
(defaultdict) with the Zonal data being the Dictionary Keys and the 
Dictionary values being the height errors.  This way, I could get my 
stats by dictionary key (zones).  If there is method to this madness?

To giving you an idea of the scope of the problem, I have 5 zonal layers 
and 50 height error raster in my study so speed is of essence.  A 
typical raster has.  284401 x 28801 pixels.

Thanks

Nicolas