[GRASS-dev] v.rast.stats parallel process
mlennert at club.worldonline.be
Thu Jun 14 07:38:57 PDT 2018
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
> 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?
> -----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...
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