[mkgmap-dev] Problems with sea in overview map

Wed May 19 15:12:11 BST 2021

Hi Ticker,

I think ShapeMergeFilter could be part of the problem. It sometimes finds strange ways to merge shapes, esp. when many small parts can be merged. Maybe this can be improved by sorting so that it merges from top to bottom.

Gerd

________________________________________
Von: mkgmap-dev <mkgmap-dev-bounces at lists.mkgmap.org.uk> im Auftrag von Ticker Berkin <rwb-mkgmap at jagit.co.uk>
Gesendet: Mittwoch, 19. Mai 2021 14:14
An: Development list for mkgmap
Betreff: Re: [mkgmap-dev] Problems with sea in overview map

Hi Gerd

I've just been experimenting and looking at shapes and rounding-to-low
-resolution can easily cause self-intersections.

It isn't just a problem with sea, or even with multipolygon hole
cutting. GPSMapEdit reports over 1000 in my test area. This number
reduces only slightly when I disable DP for polygons. Generally these
are not noticeable - a little bit of wood missing when zoomed out isn't
obvious, but same is not true of sea.

Ticker

On Wed, 2021-05-19 at 11:43 +0000, Gerd Petermann wrote:
> Hi Ticker,
>
> no need to guess, I use GpxCreator in various places to visualize
> input and output of filters. I load the gpx files into JOSM and maybe
> convert to Data layer to understand what happens, e.g. where the
> start /end point is.
> Reg. self-intersection:
> Think of a merged sea shape with several islands in it. The rounding
> may result in only three or four different nodes, visitied in a more
> or less random order while the correct shape would be a triangle or
> rectangle.
> Not sure if this is only a problem with sea, probably not.
>
> Feel free to try other orders of the filters, or maybe different
> algos to set the preserved flag. There is definitely room for
> improvements. I've played with this very often and sometimes one area
> is improved and another is worsened.
>
> Gerd

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