AW: Re: Fwd: [Qgis-user] QGIS "Near"
Giuseppe Sucameli
sucameli at faunalia.it
Mon Oct 25 05:09:32 PDT 2010
Hi all,
two days ago I wrote a similar plugin for a LD talk in Pisa.
I was unaware of the QgsSpatialIndex class (seems there's no documentation
about it in the online QGis API pages or maybe I missed it) so I wrote a
simple
loop to find the closest feature.
Now I tried also the Nearest plugin and they are different behavior!
See the scheenshots [1] [2].
AFAICS, Nearest select a wrong polygon.
I see the plugin's code and I think it could a QgsSpatialIndex bug, but it
could be
also the normal behaviour (I didn't found its documentation on the API pages
so I don't know).
I'm going to add my plugin (ClosestFeatureFinded) to the Faunalia repo so
you
can try it and check the different behavior.
I hope this can help to find the bug (if any).
If you confirm it, I'll fill a bug report.
Cheers.
[1] http://img87.imageshack.us/img87/3232/nearest.jpg
[2] http://img64.imageshack.us/img64/2066/closest.jpg
On Fri, Oct 22, 2010 at 9:19 AM, Ziegler Stefan <Stefan.Ziegler at bd.so.ch>wrote:
> there is some strange behaviour when using it with polygon features (at
> least I think it's a bit strange): sometimes when you click into a polygon I
> would expect that it selects the polygon I clicked into but it selects an
> adjacent polygon. This is probably due to the nearestNeighbor method of the
> spatial index. Since the two neighboring polygons share a common border the
> distance would be equal but the spatial index does not check if the
> coordindates of the mouse click lies within one of the two polygons.
>
> regards
> Stefan
>
> mit freundlichem Gruss
> Stefan Ziegler
>
>
> ----- Originalnachricht -----
> Von: "Jim Hammack" <hammack at GotSlack.org>
> Gesendet: Don, 21.10.2010 19:20
> An: "Ziegler Stefan" <Stefan.Ziegler at bd.so.ch>
> Cc: qgis-user <qgis-user at lists.osgeo.org>
> Betreff: Re: AW: Re: Fwd: [Qgis-user] QGIS "Near"
>
>
> Stefan,
>
>
>
> I was looking for the same functionality as Zoran so have
> also been working with your "Nearest" plugin. It is exactly
> what I need and seems to work well.
>
>
>
> Thanks!
>
> Jim
>
>
>
> On 10/20/2010 01:54 PM, Ziegler Stefan wrote:
>
>
> Hi Zoran
>
>
>
> I had some time left, took all
> my code snippets and also the one from Carson. Please try
> the plugin "Nearest" that should cover your example 1:
>
>
>
> http://www.catais.org/qgis/plugins.xml
>
>
>
> regards
>
> Stefan
>
>
> -----Ursprüngliche
> Nachricht-----
>
> Von: Zoran Jankovic [mailto:zoran.jankovic at zisis.hr]
>
> Gesendet am: Mittwoch, 20. Oktober 2010 19:21
>
> An: qgis-user
>
> Betreff: Re: Fwd: [Qgis-user] QGIS "Near"
>
>
>
> Hi Joe,
>
>
>
>
>
>
> On Wed, Oct 20, 2010 at 5:06 PM, Joe
> Larson <joelarso at gmail.com>
> wrote:
>
>
> Does the function 'snapWithContext'
>
>
> http://doc.qgis.org/head/classQgsVectorLayer.html#733b974dce13d587e05cf3d4fc24f208
>
> which "Snaps to segment or vertex within given tolerance."
> seem like
>
> what you're looking for? I came across it while trying to
> get Quantum
>
> Navigator working recently...seemed relative, but I'm no
> expert!
>
>
>
>
>
>
>
> This is similar to the mentioned solution with
> selecting by radius, or changing the tolerance of ID tool.
> Close, but no cigar. Since this is not very urgent, I've
> decided to continue pursuing that outlined solution Carson
> gave, and write a plugin i Python based on that. Since I
> actually never used Python before, it may take a while,
> but hey, I get to learn sth. new :-).
>
> I never got the word back from Carson, has he developed
> anything along these lines, but I have to presume he
> didn't...
>
> Anyone interested in joning me, or even earning some
> money, is still invited to jump on board. My GIS
> implementation project is well on the way, and it seems
> there'll even be some money involved :-).
>
>
>
> Zoran
>
>
>
>
>
> ~joe
>
>
>
> On Tue, Oct 19, 2010 at 9:55 AM, Andreas Neumann
> <a.neumann at carto.net>wrote:
>
>
>
>
> > Hi Zoran,
>
> >
>
> > I believe the infrastructure of what you want is
> already wihtin the
>
> > selection and identify tools in QGIS. Isn't this
> almost implemented in the
>
> > current identify tool?
>
> >
>
> >
>
> It sort of is, but not completely. Identify will ID
> all the features within
>
> certain radios (percentage of extent), but it will ID
> _all_ of the features
>
> within this radius. I only need the nearest, no matter
> how far away... Let
>
> us say it is, for simplicity, within current extent.
>
>
>
>
>
> > The current identify tool selects "near" or
> "close by" features within a
>
> > certain tolerance. This tolerance can be set in
> "Options" --> "Map tools"
>
> > "search radius". I believe it currently only
> effects the identify tool. Do
>
> > you want the same tolerance also be used for the
> click-selection tool?
>
> >
>
> >
>
> Look above. This could be useful, but it is not the
> functionality I'm
>
> currently looking after.
>
>
>
>
>
> > Are you also aware that in QGIS 1.6 there are new
> selection tools?
>
> >
>
> > * by click
>
> > * by rectangle
>
> > * by polygon
>
> > * by freehand
>
> > * by radius
>
> >
>
> >
>
> Yup, these are great, but they all select _multiple_
> features within radius,
>
> rectangle, etc.
>
>
>
>
>
> > Maybe this also helps to address your needs?
>
> >
>
> > Of course you can combine it with previous
> selections by pressing the ctrl
>
> > key.
>
> >
>
> >
>
>
>
> BR,
>
>
>
>
>
> ---
>
> Zoran Jankovic
>
> ZIS-Izrada softvera i savjetovanje / ZIS - Software
> Development and
>
> Consulting
>
>
>
> http://www.zisis.hr
>
>
>
> M: 00 385 98 682 902
>
> T: 00 385 44 683 374
>
>
>
> A. Senoe 4
>
> 44320 Kutina
>
> Croatia
>
>
>
>
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--
Giuseppe Sucameli
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