[Qgis-developer] Geom collection and QGIS (was QgisLogger can be a serious bottleneck)

Sat Jul 5 11:10:03 PDT 2014

Is wrong.
The geos return a collection when the collectionis the right result.

if the result is a collection like:
collection (multipolygons, multilinestrings, multipoint)

why it should remove the lines and points.

It could be useful to the client.
The fact that the client is capable to understand only point/line and
polgons is a problem of the client , not of the geos.

If the invoker is not capable to understand collection, but it want do
operation that could return collection.
The invoker (the client) should increase him matematics capability ,
not decrease the capability of geos.
:)

In postgis and spalite is easy manage this kind of situation even if
the table is not a collection.

With a  "ExtractFromCollection(ForceToCollection(geometry)..)"
you can easily to resolve the problem on postgis/spatialite.

If this capability is not available in qgis is a problem of qgis not of geos.

:)

A.

2014-07-05 17:23 GMT+02:00 G. Allegri <giohappy at gmail.com>:
> (I changed the topic)
>
> Geometry collections in QGIS must be treated at the GEOS level.
> There isnt a QGIS::wkbType for geometry collections, so if GEOS return a
> collection they must be managed as GEOS geometries, before "moving them up"
> to QgsGeometry.
>
> Correct me if I'm wrong.
>
> giovanni
>
>
> 2014-07-05 17:17 GMT+02:00 Andrea Peri <aperi2007 at gmail.com>:
>>
>> Thx GioHappy, this is imprtant for me to know.
>>
>> So is surely better to use the postgis or spatialite
>> because it allow you to extract from the collection the section with
>> the right type.
>>
>> If you do a difference beetwen two polygons is the result is a
>> collection with a polygon section and a point section.
>> You should extract the polygon and discard the point.
>> If the strategu is discard all the collection this mean that on qgis
>> the difference could lost domething of important and so potentially
>> the difference do a wrong result.
>>
>> Regards,
>> Andrea.
>>
>>
>> 2014-07-05 16:47 GMT+02:00 G. Allegri <giohappy at gmail.com>:
>> > 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
>> >> >> >>
>> >> >> >> _______________________________________________
>> >> >> >> Qgis-developer mailing list
>> >> >> >> Qgis-developer at lists.osgeo.org
>> >> >> >> http://lists.osgeo.org/mailman/listinfo/qgis-developer
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> >
>> >> >> > --
>> >> >> > Giovanni Allegri
>> >> >> > http://about.me/giovanniallegri
>> >> >> > Twitter: https://twitter.com/_giohappy_
>> >> >> > blog: http://blog.spaziogis.it
>> >> >> > GEO+ geomatica in Italia http://bit.ly/GEOplus
>> >> >> >
>> >> >> > _______________________________________________
>> >> >> > Qgis-developer mailing list
>> >> >> > Qgis-developer at lists.osgeo.org
>> >> >> > http://lists.osgeo.org/mailman/listinfo/qgis-developer
>> >> >>
>> >> >>
>> >> >>
>> >> >> --
>> >> >> -----------------
>> >> >> 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
>>
>>
>>
>> --
>> -----------------
>> 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
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