[mkgmap-dev] removal of parallel lines

Tue Mar 9 07:06:51 GMT 2021

Hi Mike,

the detection of parallel lines isn't easy. The housenumber code contains code to detect this but it fails in some situations (and it works with the high precision points, not with the results of the heavy rounding at lower levels. On the other hand it has to cope with sidewalks and service roads going parallel to main roads, so for your special case it might be possible to do better calculations.
The main problem for me was that a road is split into several OSM ways, and the housenumber code has to cope with the fragments that are written to NET.
In your case you can try to combine all motorways first and calculate a replacement line for the non-routable overview levels.

Reg. the zig-zagging lines I think it isn't the Douglas-Peucker filter, it's the rounding that causes trouble. So, the points of the replacement lines should be calculated in a way that produces stable results for the different levels of rounding.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Mike Baggaley <mike at tvage.co.uk>
Gesendet: Dienstag, 9. März 2021 00:54
An: 'Development list for mkgmap'
Betreff: [mkgmap-dev] removal of parallel lines

Hi all,

At low resolutions I would like to be able to remove parallel lines so that
(for example) only a single motorway carriageway or railway track is shown
instead of  two or (in the case of the West Coast Main Line) four lines,
which due to different Douglas Peucker line simplifications end up crossing
each other, look messy and add unnecessary lines to the overview.

Has anyone done this before or have any ideas about how I might go about it?

Cheers,
Mike

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