[Qgis-developer] QgisLogger can be a serious bottleneck

Sat Jul 5 07:47:20 PDT 2014

AFAICS whenever a new feature needs to be created, geom collections are
discarded, because QGIS cannot manage them.

giovanni

2014-07-05 16:40 GMT+02:00 Andrea Peri <aperi2007 at gmail.com>:

> Ok, sorry.
>
> Just a my personal curiosity:
> The difference could give also a collection not empty.
> If the difference of two polygons is a collection with some polygons,
> some lines and some points.
> What happened to this collection in QGIS ?
>
> Thx,
> A.
>
>
> 2014-07-05 16:03 GMT+02:00 G. Allegri <giohappy at gmail.com>:
> > Hi Andrea, as I said above I'm not considering it an error.
> > The topic of this post is QGIS message logging.
> > The processing completes as expected, with the same results as Spatialite
> > and PostGIS. These simply do it silently :)
> >
> > giovanni
> >
> >
> >
> > 2014-07-05 15:59 GMT+02:00 Andrea Peri <aperi2007 at gmail.com>:
> >
> >> Hi GioHappy,
> >>
> >> the empty-collection is absolutelly not necessarylly a bug.
> >> It is the obviously result of an operation on a machine (like the
> >> computer) with a binary finite arithmetic.
> >>
> >> Usually the empty is due to a too low value to be describe with a
> >> finite binary arithmetic.
> >>
> >> If the dataset is small or it is topologically correct (this not mean
> >> only to be snapped).
> >>  the collection results never happened.
> >> Instead if the dataset is not topologically correct and is big the
> >> probability to have some collection result grow.
> >> We tipically have alway an 0.01% of collection on our results.
> >>
> >> I suggest you to use directly postgis or spatialite to do this kind of
> >> operations.
> >>
> >> In these products you have the useful tools to resolve the collections
> >> correctly.
> >>
> >> Regard,
> >>
> >> Andrea.
> >>
> >>
> >> 2014-07-05 12:40 GMT+02:00 G. Allegri <giohappy at gmail.com>:
> >> > Hi Jurgen,
> >> > I wouldn't call them errors. GEOSDIfference returned a lot of empty
> >> > geomcollections, which the QgsVectorFileWriter couldn't manage.
> >> > Consequently
> >> > it wrote a log message for each geometry it couldn't write [1].
> >> >
> >> > Surely the logging should be improved in this specific case. Anyway, I
> >> > think
> >> > the option to turn QgsMessageLog off could be useful anyway...
> >> >
> >> > giovanni
> >> >
> >> > [1]
> >> >
> >> >
> https://github.com/qgis/QGIS/blob/master/src/core/qgsvectorfilewriter.cpp#L1718
> >> >
> >> >
> >> > 2014-07-05 12:31 GMT+02:00 Jürgen E. <jef at norbit.de>:
> >> >
> >> >> Hi Giovanni,
> >> >>
> >> >> On Sat, 05. Jul 2014 at 10:27:24 +0200, G. Allegri wrote:
> >> >> > As I reported in a previous post, I was unable to conclude a
> >> >> > difference
> >> >> > operation on a vector because the tool was running in exponential
> >> >> > time.
> >> >>
> >> >> > Debugging pointed me to the problem: QgsVectoFileWriter was logging
> >> >> > tons
> >> >> > of
> >> >> > empty geometres with an incompatible type which will be discarded.
> >> >> > After commenting the line of logging the process completed in
> linear
> >> >> > time.
> >> >>
> >> >> > Shouldn't we offer the opportunity to turn QgsLogger off? This
> would
> >> >> > let
> >> >> > the user/developer to switch it off whenever he already knows
> what's
> >> >> > happening.
> >> >> > Is it already there and I missed it?
> >> >>
> >> >> What error message did you get and wouldn't it be better to kill them
> >> >> where it
> >> >> origins or to issue a final "%n empty geometries skipped" instead of
> >> >> logging
> >> >> individual errors.
> >> >>
> >> >> Alternatively we could issue a "last message repeated %n times" in
> >> >> message
> >> >> log
> >> >> to make it behave better - although that only works the error message
> >> >> are
> >> >> identical.
> >> >>
> >> >>
> >> >> Jürgen
> >> >>
> >> >> --
> >> >> Jürgen E. Fischer           norBIT GmbH             Tel.
> >> >> +49-4931-918175-31
> >> >> Dipl.-Inf. (FH)             Rheinstraße 13          Fax.
> >> >> +49-4931-918175-50
> >> >> Software Engineer           D-26506 Norden
> >> >> http://www.norbit.de
> >> >> QGIS release manager (PSC)  Germany                    IRC: jef on
> >> >> FreeNode
> >> >>
> >> >> --
> >> >> norBIT Gesellschaft fuer Unternehmensberatung und Informationssysteme
> >> >> mbH
> >> >> Rheinstrasse 13, 26506 Norden
> >> >> GF: Jelto Buurman, HR: Amtsgericht Emden, HRB 5502
> >> >>
> >> >> _______________________________________________
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> >> >
> >> >
> >> >
> >> >
> >> > --
> >> > Giovanni Allegri
> >> > http://about.me/giovanniallegri
> >> > Twitter: https://twitter.com/_giohappy_
> >> > blog: http://blog.spaziogis.it
> >> > GEO+ geomatica in Italia http://bit.ly/GEOplus
> >> >
> >> > _______________________________________________
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> >>
> >>
> >>
> >> --
> >> -----------------
> >> Andrea Peri
> >> . . . . . . . . .
> >> qwerty àèìòù
> >> -----------------
> >
> >
> >
> >
> > --
> > Giovanni Allegri
> > http://about.me/giovanniallegri
> > Twitter: https://twitter.com/_giohappy_
> > blog: http://blog.spaziogis.it
> > GEO+ geomatica in Italia http://bit.ly/GEOplus
>
>
>
> --
> -----------------
> Andrea Peri
> . . . . . . . . .
> qwerty àèìòù
> -----------------
>

-- 
Giovanni Allegri
http://about.me/giovanniallegri
Twitter: https://twitter.com/_giohappy_
blog: http://blog.spaziogis.it
GEO+ geomatica in Italia http://bit.ly/GEOplus
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