[mkgmap-dev] [PATCH v3] Mp merge: generate-sea: bugfix for generate-sea=multipolygon

Sun Jan 17 22:36:55 GMT 2010

>
> WanMil,
>
> Good news - I don't think it's your problem. I disabled the sea
> generation completely and the lines on the tile edges are still there.
>
> Haven't a clue what's causing them (and I don't care because they don't
> show up when I use generate-sea=polygons).
>
> One issue that I don't think you can do much about is that mapsource
> tends to show horizontal and vertical gaps between polygons when you
> zoom out. They are a bit weird because they come and go as you pan and
> zoom. Having polygons for sea (as opposed to having polygons for land,
> which is what I have been using) means that you get more
> artifacts visible when using mapsource. That's a shame but may well not
> be a problem when viewing the map on a real gps.
>
> Anyway, your new MP code is producing great results (and it's quick).
>
> Mark
>

Mark,

thanks a lot!

I did have a bad test... I generated a map of belgium with 
generate-sea=multipolygon,no-sea-sectors and whole belgium is flodded :-(

BUT I found out that some of the coastline segments are missing or are 
not completely contained in the OSM dump, so that's no shame for mkgmap.

I think it's a general problem that the osm dumps do not contain any 
detailed information about the shape that was used to cut out the OSM 
data. Without this shape we don't have a good chance to detect the edges 
and to close open polygons.
Maybe we can propose this to the next version of the API?

Another idea is to introduce a kind of ShapeDetector which tries to 
regenerate the original shape of a tile / OSM dump. I don't have a good 
idea how to do this and I have less idea how to do this in acceptable time.
Maybe we can use an java.awt.geom.Area object and add all lines with a 
dimension of 1 unit. At the end of reading the OSM file we could get the 
outer shape from the area object. But I don't think that this is quick.....

Anyhow the mp code of my patch is not the solution for all but at the 
moment it improves the handling of multipolygons very much compared to 
the current trunk. And after committing I think I will get some more 
feedback from other map generators which will help to improve things.

WanMil