[GRASS-user] How does GRASS do tiled processing?

[Jonathan Greenberg]

Milton:

    Thanks, but I'm more curious in just the generic way GRASS does 
tiled processing (say, in mapcalc).  I assume there is a low-level 
processing layer GRASS uses (or no?).  I'm not doing a direct grass-to-R 
link, I'm doing the processing completely within R with rgdal, but I'm 
interested in various solutions to the tiled processing problem.

    That is a helpful suggestion, tho -- I used a similar approach when 
I "forced" r.sun to do tiled processing with a massive lidar image I had 
-- I ended up setting overlaps between each tile since its a spatial 
problem.  For pure pixel analyses, of course, there's no need to worry 
about boundaries...

--j

Milton Cezar Ribeiro wrote:
> Hi Jonathan,
>  
> When I need to do tiles processing of grass coupled R, I usually set a 
> list of bounding boxes on R (a list of x1, x2, y1, y2), and then I put 
> it on a for() looping. So, I set a new g.region using n= s= e= and w= 
> parameters using system() function of R (you can do it of other ways). 
> Just after the for() I reset g.region with -d.
>  
> *but* you need to be very careful with your processing, because some 
> of the results will be influenced by the boundary of new sub-regions.
>  
> Good luck
>  
> milton
> brazil=toronto
>
> 2009/7/8 Jonathan Greenberg <greenberg at ucdavis.edu 
> <mailto:greenberg at ucdavis.edu>>
>
>     GRASSers:
>
>       I was curious -- how is tiled processing realized in GRASS GIS?
>      Is there a fixed input tile size (in MB of RAM or # of lines)?
>      Is there some documentation buried on the GRASS site that
>     describes the algorithm?  I'm trying to replicate an efficient
>     tiled approach in R -- I was basing it off the ENVI approach
>     (precalculate the input data memory footprint per line of data,
>     read in as many lines as the memory cap allows, process, write
>     those lines, rinse, repeat), but I was curious if GRASS had a
>     different approach.
>
>     --j
>
>     -- 
>
>     Jonathan A. Greenberg, PhD
>     Postdoctoral Scholar
>     Center for Spatial Technologies and Remote Sensing (CSTARS)
>     University of California, Davis
>     One Shields Avenue
>     The Barn, Room 250N
>     Davis, CA 95616
>     Cell: 415-794-5043
>     AIM: jgrn307, MSN: jgrn307 at hotmail.com
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-- 

Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N
Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307, MSN: jgrn307 at hotmail.com, Gchat: jgrn307