[GRASS-dev] v.rast.stats parallel process

[Moritz Lennert]

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 
> <Stefan.Blumentrath at nina.no <mailto:Stefan.Blumentrath at nina.no>>:
> 
>     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 <grass-dev-bounces at lists.osgeo.org
>     <mailto:grass-dev-bounces at lists.osgeo.org>> On Behalf Of Moritz Lennert
>     Sent: torsdag 14. juni 2018 13:05
>     To: Lorenzo Bottaccioli <lorenzo.bottaccioli at gmail.com
>     <mailto:lorenzo.bottaccioli at gmail.com>>; GRASS developers list
>     <grass-dev at lists.osgeo.org <mailto:grass-dev at lists.osgeo.org>>
>     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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