[GRASS-user] How GRASS loads raster images into memory?

Benjamin Ducke benducke at fastmail.fm
Fri Aug 16 06:14:01 PDT 2013


Basically, GRASS reads rasters row-by-row.
But it is up to the individual module to
keep more than one row in memory to speed
up calculations. That is why some GRASS modules
have options for the user to adjust the amount
of raster data to be cached in memory.

The GRASS raster engine is very well documented
in the GRASS developers manual:


(for GRASS 6)



On 08/16/2013 03:08 PM, Andranik Hayrapetyan wrote:
> Good day,
> I would like to understand how GRASS loads raster images into memory to
> perform calculations on them.
> Does it load the entire image into memory and only then do the
> calculation on them, or it loads image into memory by portions sequentially?
> Or may be this depends on specific module?
> In particular I am interested in 2 modules: *r.mapcalc* and *r.patch*.
> In my experiments I had strong feeling that it loads image into memory
> by portions, because the usage of memory during the calculation was not
> big but the HDD I/O was continuous and quite aggressive...
> Any answer or links to documentation about this issue can help me a lot.
> Thanks in advance!
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Dr. Benjamin Ducke, M.A.
{*} Geospatial Consultant
{*} GIS Developer

   benducke at fastmail.fm

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