[mkgmap-dev] nearby-POI: What to do with several POI arranged on a circle?

Thu May 7 10:28:53 BST 2020

Hi Gerd

The bench in lake problem is avoided by the user not using the merge-at
-mid-point option. Possibly making the delete-poi option keep the most
central one and delete the rest.

Ticker 

On Thu, 2020-05-07 at 09:12 +0000, Gerd Petermann wrote:
> Hi Ticker,
> 
> I should have used amenity=bench in the example, this is a bit more
> realistic, but the default style doesn't generate a POI for that.
> 
> I've found a rather simple iterative algo to fix the problem, but
> what I really wanted to point out is that the result can look really
> wrong.
> Benches are often arranged around something, e.g. a small lake/pond.
> I think nobody wants a map that shows a bench in the middle of a
> lake.
> OTHO, bus stops typically come in pairs, but maybe 50m apart. It
> seems reasonable to merge them in the middle.
> 
> Gerd
> 
> ________________________________________
> Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag
> von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
> Gesendet: Donnerstag, 7. Mai 2020 10:21
> An: Development list for mkgmap
> Betreff: Re: [mkgmap-dev] nearby-POI: What to do with several POI
> arranged on a circle?
> 
> Hi
> 
> The problem is in the point grouping algo, rather than anything to do
> with the merge-at-mid-point option.
> 
> Although an interesting problem to solve, it seems to be getting
> excessive. The simple logic in the last versions seemed to solve most
> users's problems and make them happy.
> 
> Ticker
> 
> 
> On Thu, 2020-05-07 at 07:42 +0000, Gerd Petermann wrote:
> > Hi all,
> > 
> > while doing further tests I've found this edge case (see attached
> > file)
> > Draw a circle with a diameter of ~56m and tag all nodes
> > amenity=bank.
> > The default style has
> > amenity=bank [0x2f06 resolution 24]
> > 
> > With --nearby-poi-rules=0x2f06:30:merge-at-mid-point one might
> > expect
> > a single POI in the middle of the circle, but the result is
> > different:
> > Since there is no POI near the center of the circle the current
> > algo
> > finds 4 groups, all close to the edge of the circle.
> > 
> > I think for merge-at-mid-point I need a different algo. I'm looking
> > at https://en.wikipedia.org/wiki/Cluster_analysis now.
> > 
> > Gerd
> > 
> > 
> > 
> > _______________________________________________
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> > mkgmap-dev at lists.mkgmap.org.uk
> > http://www.mkgmap.org.uk/mailman/listinfo/mkgmap-dev
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