AW: AW: Re: Fwd: [Qgis-user] QGIS "Near"

Ziegler Stefan Stefan.Ziegler at bd.so.ch
Tue Oct 26 09:25:22 PDT 2010


Hi 

I'm also quite sure there is some unexpected behaviour in the QgsSpatialIndex.nearestNeighbor() method. The two screenshots look a bit like it has something to do with the bounding box? 

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.





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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