AW: Re: Fwd: [Qgis-user] QGIS "Near"
Giuseppe Sucameli
sucameli at faunalia.it
Thu Oct 28 08:29:11 PDT 2010
Hi Stefan,
On Thu, Oct 28, 2010 at 7:48 AM, Ziegler Stefan <Stefan.Ziegler at bd.so.ch>wrote:
> thanks for looking into this. Do you think it's worth filling out a bug
> report since the nearestNeighbor method does not the keep the promise or is
> this the normal behaviour of a spatial index based method?
>
I think we should fill a bug report because the nearestNeighbor doesn't work
as
expected.
I don't know if the QgsSpatialIndex can be improved to manage complex
geometries,
but AFAICS in the few inline comments within the code, in this moment it
manages only
Points, Lines and Regions (rectangles), so every polygonal geometry must be
converted to Regions.
This issue could take a lot of time to be fixed, but we can use the ticket
to require
the documentation about the QgsSpatialIndex class. In this moment it's
missing.
Cheers.
> ----- Originalnachricht -----
> Von: "Giuseppe Sucameli" <sucameli at faunalia.it>
> Gesendet: Mit, 27.10.2010 17:30
> An: "Ziegler Stefan" <Stefan.Ziegler at bd.so.ch>
> Cc: "Jim Hammack" <hammack at gotslack.org> ; qgis-user <
> qgis-user at lists.osgeo.org>
> Betreff: Re: AW: Re: Fwd: [Qgis-user] QGIS "Near"
>
> Hi Stefan,
> your workaround works fine in my case!
>
> I looked at the QgsSpatialIndex code and I have bad news... It uses the
> bounding box
> of the geometries!
> This means that your workaround can work in a lot of cases but not in all
> cases, e.g. if
>
>
> you have more than N geometries (10 considering your workaround), ones
> inside
> each other.
>
> Cheers.
>
> On Tue, Oct 26, 2010 at 6:47 PM, Ziegler Stefan <Stefan.Ziegler at bd.so.ch>
> wrote:
>
>
>
> Hi Giuseppe
>
>
>
> I wrote a little workaround. Could you please update to 0.0.6 and check it
> with your test case? Thanks.
>
>
>
> regards
>
> Stefan
>
>
>
> mit freundlichem Gruss
>
> Stefan Ziegler
>
>
>
>
>
> ----- Originalnachricht -----
>
> Von: "Giuseppe Sucameli" <sucameli at faunalia.it>
>
> Gesendet: Mon, 25.10.2010 14:09
>
> An: "Ziegler Stefan" <Stefan.Ziegler at bd.so.ch>
>
> Cc: "Jim Hammack" <hammack at gotslack.org> ; qgis-user <
> qgis-user at lists.osgeo.org>
>
>
>
> Betreff: Re: AW: Re: Fwd: [Qgis-user] QGIS "Near"
>
>
>
> 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.
>
>
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>
>
> 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"
>
>
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> Stefan,
>
>
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>
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> 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.
>
>
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> Thanks!
>
>
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>
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>
> Jim
>
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> On 10/20/2010 01:54 PM, Ziegler Stefan wrote:
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> Hi Zoran
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> 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:
>
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> http://www.catais.org/qgis/plugins.xml
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> regards
>
>
>
>
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>
>
> Stefan
>
>
>
>
>
>
>
>
>
>
>
> -----Ursprüngliche
>
>
>
> Nachricht-----
>
>
>
>
>
>
>
> Von: Zoran Jankovic [mailto:zoran.jankovic at zisis.hr]
>
>
>
>
>
>
>
> Gesendet am: Mittwoch, 20. Oktober 2010 19:21
>
>
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> An: qgis-user
>
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> Betreff: Re: Fwd: [Qgis-user] QGIS "Near"
>
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> Hi Joe,
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> On Wed, Oct 20, 2010 at 5:06 PM, Joe
>
>
>
> Larson <joelarso at gmail.com>
>
>
>
> wrote:
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> Does the function 'snapWithContext'
>
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> http://doc.qgis.org/head/classQgsVectorLayer.html#733b974dce13d587e05cf3d4fc24f208
>
>
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>
>
>
> which "Snaps to segment or vertex within given tolerance."
>
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> seem like
>
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> what you're looking for? I came across it while trying to
>
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> get Quantum
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> Navigator working recently...seemed relative, but I'm no
>
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>
> expert!
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> This is similar to the mentioned solution with
>
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> selecting by radius, or changing the tolerance of ID tool.
>
>
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> 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 :-).
>
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> I never got the word back from Carson, has he developed
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> anything along these lines, but I have to presume he
>
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> didn't...
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> 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
>
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> there'll even be some money involved :-).
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> Zoran
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> ~joe
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> On Tue, Oct 19, 2010 at 9:55 AM, Andreas Neumann
>
>
>
> <a.neumann at carto.net>wrote:
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> > Hi Zoran,
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> >
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> > I believe the infrastructure of what you want is
>
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> already wihtin the
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> > selection and identify tools in QGIS. Isn't this
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> almost implemented in the
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> > current identify tool?
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> >
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> >
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> It sort of is, but not completely. Identify will ID
>
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> all the features within
>
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> certain radios (percentage of extent), but it will ID
>
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> _all_ of the features
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> within this radius. I only need the nearest, no matter
>
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> how far away... Let
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> us say it is, for simplicity, within current extent.
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> > The current identify tool selects "near" or
>
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> "close by" features within a
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> > certain tolerance. This tolerance can be set in
>
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> "Options" --> "Map tools"
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> > "search radius". I believe it currently only
>
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> effects the identify tool. Do
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> > you want the same tolerance also be used for the
>
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> click-selection tool?
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> >
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> >
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> Look above. This could be useful, but it is not the
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> functionality I'm
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> currently looking after.
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> > Are you also aware that in QGIS 1.6 there are new
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> selection tools?
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> >
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> > * by click
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> > * by rectangle
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> > * by polygon
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> > * by freehand
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> > * by radius
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> Yup, these are great, but they all select _multiple_
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> features within radius,
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> rectangle, etc.
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> > Maybe this also helps to address your needs?
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> >
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> > Of course you can combine it with previous
>
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> selections by pressing the ctrl
>
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> > key.
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> BR,
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> ---
>
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> Zoran Jankovic
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>
> ZIS-Izrada softvera i savjetovanje / ZIS - Software
>
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> Development and
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> Consulting
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> http://www.zisis.hr
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> M: 00 385 98 682 902
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> T: 00 385 44 683 374
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> _______________________________________________
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> _______________________________________________
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> _______________________________________________
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>
> Qgis-user mailing list
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> --
>
> Giuseppe Sucameli
>
>
>
>
>
>
>
> --
> Giuseppe Sucameli
>
>
> _______________________________________________
> Qgis-user mailing list
> Qgis-user at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-user
>
--
Giuseppe Sucameli
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