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

[Lorenzo Bottaccioli]

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.

Ciao,

Lorenzo

2018-06-14 13:20 GMT+02:00 Stefan Blumentrath <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 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> On Behalf Of Moritz
> Lennert
> Sent: torsdag 14. juni 2018 13:05
> To: Lorenzo Bottaccioli <lorenzo.bottaccioli at gmail.com>; GRASS developers
> list <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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