[mkgmap-dev] Terraced/pixellated coastline with --precomp-sea

Sat Feb 18 11:29:06 GMT 2017

After playing around some more I think I found the reason for the problem. It
appears that there is a conflict between the --min-size-polygon= parameter
and sea generation from the precompiled files.

For larger Values of --min-size-polygon, the tearracing becomes worse. For
smaller values it becomes better. It seems that the generated sea polygons
are filtered one at a time by --min-size-polygon.

Which is probably a bug. With the default setting for --generate-sea or an
explicit --generate-sea=multipolygon, the sea is supposed to be generated as
a multipolygon. It does not make sense to filter out individual parts of a
multipolygon. Multipolygons on land are treated as a whole, and the same
should be true for generated sea polys.

But it looks like the --precomp-sea option creates many individual sea
polygons, not a multipolygon as described in the documentation.

I think the simple solution would be to not apply the --min-size-polygon
filter to generated sea at all. A coastline multipolygon usually extends
over large parts of the map, so it would be never filtered.

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