Re: [JPP-Devel] Has anybody done a "Nearest N" tool yet?

[Michaël M. <mic...@fr...>]

Hi,

Interesting problem. Last time I had search nearest features around a 
feature f, I wrote a script doing the following
1) index the dataset to search with STRtree
2) initiate the search with a small distance d
3) search for features in a bounding box equals to bounding box of f + 
distance d in all directions
     if features are found, select the nearest of them (or k nearest) by 
a linear search
     else set d = 2d and reiterate 3)

Could be implemented as described above in OpenJUMP, but I suspect there 
are better algorithms which could take place in JTS itself

See also
http://en.wikipedia.org/wiki/Nearest_neighbor_search
and the interesting discussion started today on JTS list

Michaël

Le 20/04/2011 16:21, Rahkonen Jukka a écrit :
> Hi,
> I am just thinking what could be cool to have, I do not have any 
> immediate need right now myself. However, I would say that the answer 
> in both. I have some ideas about improving the OpenJUMP GPS extension 
> for making OJ into a nice vector based moving map program. N nearest 
> items from a point would suit that use case. I mean queries like Find 
> the closest gas station / restaurant / streetname / maxspeed limit 
> from my current GPS location etc.
> For more serious work with vector data sets, risk analysis and that 
> sort of things the N items nearest to selected item would probably be 
> more useful.  And of course the selected item can be a point as well.  
> Your description makes me think that you have a ready tool for the 
> latter use case. It would be interesting to test it.
> -Jukka Rahkonen-
>
>     ------------------------------------------------------------------------
>     Larry Becker  wrote:
>     Hi Jukka,
>
>       Do you want to find the N items nearest to a point or another
>     item?  I have a tool that looks out a specified distance from a
>     selected feature and creates a new layer containing lines with
>     arrowheads between all of the features.  It puts the length in an
>     attribute so you can use it as a label.  You can then sort by the
>     length attribute to get the N nearest.
>
>     regards,
>
>     Larry B.
>
>
>
>     On Wed, Apr 20, 2011 at 7:44 AM, Rahkonen Jukka
>     <Juk...@mm... <mailto:Juk...@mm...>> wrote:
>
>         Hi,
>         I can find nearest features by having a source layer and
>         a mask layer and doing a spatial query "is within distance" by
>         incrementally increasing the distance parameter. It would
>         be nice to have a tool or script for doing this
>         automatically.  Even better if the number of features to be
>         found could be given with another parameter and the actual
>         distance would be written into the attribute table of the
>         result layer. Has anybody done this yet?
>         The selection tool "Select Items by Circle from Selected
>         Layers" might be usable also if it could be done dynamic so
>         that user could click at the centre point and drag for giving
>         the radius before OJ performs the query.
>         I know I can do what I wand with PostGIS and I guess it is
>         doable in a similar way with Spatialite but sometimes it would
>         be handy to search nearest features from shapefiles simply
>         from OJ map window.
>         -Jukka Rahkonen-
>
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