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

Thu May 7 10:12:59 BST 2020

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
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