On 14/06/18 16:31, Lorenzo Bottaccioli wrote:
Hi Moritz,
No I mean to process in parallel the stats over many vector entities for
example areas. Immagine a large raster with many polygons that want to
know the mean or max value in the area.
Ok. As the module is a scripted fronted to r.univar, the question is
more for r.univar then. Parallizing that will probably be a bit more
complicated.
Moritz
Ciao,
Lorenzo
2018-06-14 13:20 GMT+02:00 Stefan Blumentrath
<[email protected] <mailto:[email protected]>>:
Yes, access to attributes would be a challenge / bottleneck for
parallelisation, esp. if you have many areas in your vector map.
Note that not only SQLite but also DBF is still supported (which
puts some limitations)...
Please note also: https://trac.osgeo.org/grass/ticket/3523
<https://trac.osgeo.org/grass/ticket/3523> for some suggestions for
speeding up v.rast.stats (without parallelisation).
Once multiple raster map input is supported, statistics could be
computed in parallel for each raster map and then finally uploaded
to the attribute table in one single process...
Yet, the region adjustment performed by v.rast.stats would then have
to be handled differently from current solution...
I would say it is worth a ticket...
If you want a text file, you could use r.univar directly, no?
Cheers
Stefan
-----Original Message-----
From: grass-dev <[email protected]
<mailto:[email protected]>> On Behalf Of Moritz Lennert
Sent: torsdag 14. juni 2018 13:05
To: Lorenzo Bottaccioli <[email protected]
<mailto:[email protected]>>; GRASS developers list
<[email protected] <mailto:[email protected]>>
Subject: Re: [GRASS-dev] v.rast.stats parallel process
On 14/06/18 12:24, Lorenzo Bottaccioli wrote:
> Hi all,
>
> There is any chance that the v.rast.stats will be paralellized?
You mean to treat several rasters at the same time ?
It shouldn't be too complicated to write a wrapper script for this.
I would imagine the biggest problem to be the handling of the access
to the attribute database file. Not sure that you can have
concurrent access to this file by several parallel processes. If
this is an issue, we would probably have to add the option to output
v.rast.stats results to text files and then load content of these
files into at the attribute table of the vector map at the end...
Moritz
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