[mkgmap-dev] Problems with sea in overview map

Wed May 19 13:14:17 BST 2021

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