[mkgmap-dev] Multipolygon artificial tagging

Wed Feb 17 21:49:10 GMT 2010

Hi WanMil,

> the patch for the mp code does not remove any tags from the source
> polygons and lines. Instead it tags all mp-source lines and polygons
> with mkgmap:mp_source=yes.
> 
> All artificially created polygons during the mp processing are tagged
> with mkgmap:mp_created=yes.
> 
> Example:
> Polygon A - natural=water, role=outer
> Polygon B - landuse=grass, role=inner
> 
> Result after mp processing
> Polygon A - natural=water, role=outer, mkgmap:mp_source=yes
> Polygon B - landuse=grass, role=inner, mkgmap:mp_source=yes
> 
> Polygon A1 - natural=water, mkgmap:mp_created=yes
> Polygon A2 - natural=water, mkgmap:mp_created=yes
> Polygon B1 - landuse=grass, mkgmap:mp_created=yes
> 
> Maybe you could play a bit with this and post any new ideas how to
> improve the tag handling in the mp code.

How would this remove the bogus boundary lines in Germany? (Germany  
uses multipolygons for administrative boundaries.) I believe that for  
those to work, the multipolygon code should be disabled by a style  
rule, e.g., use the MP code only if type=multipolygon & boundary!=*.  
Someone who wants to render boundaries as multipolygons would enable  
the MP processing of the boundaries. Or would we make this by an  
option, something like mkgmap --disable-multipolygon='boundary=*'?

An alternative to disabling MP processing would be to set  
mkgmap:mp_created only on the line segments that were created when  
splitting A to A1 and A2, but I suppose that polygons and lines are  
wholly different entities in mkgmap, and thus you cannot have  
differently tagged line segments within a polygon.

	Marko