[mkgmap-dev] [PATCH v1] Optimize filters for shapes

Fri Jan 18 07:51:17 GMT 2013

Hi WanMil,

> >
> 
> Reducing the img file size is a nice subeffect. As long as I don't know 
> for sure that spikes are not an error I would avoid to leave them in the 
> img.

I agree.

> 
> Sometimes the result of the RoundCoordsFilter is an invalid polygons, 
> which means the polygon might be self intersecting and/or contains 
> spikes and holes as it could be seen in my example. These invalid 
> polygons are forwarded to other filters.
> 
> To be honest: I haven't checked if my example polygon looks bad in the 
> map. But checking the code I see the following might happen:
> 1. RoundCoordsFilter creates an invalid polygon with hole
> 2. PolygonSplitterFilter might split the polygon because it is too 
> large. It converts the polygon to a java.awt.geom.Area object, splits it 
> into two halves and converts it back in the method 
> PolygonSplitterBase.areaToShapes(..) method. This method does not check 
> the orientation of the returned polygons and therefore converts the hole 
> to same type the polygon has - in other words the hole is removed.
> 
> Of course we could say this is an error of the 
> PolygonSplitterBase.areaToShapes(..) method (and we can fix it) but I 
> think it would be worthy to check and optimize the whole chain a polygon 
> goes through. Maybe we find needless steps we can remove, maybe we find 
> other errors we can fix and maybe we can improve some steps which will 
> improve the overall results. At the moment I guess nobody can say for 
> sure what really happens in the long chain.

Yes, I got the same impression. I started to add some 
createGPX calls to be able to compare the input 
coming from StyledConverter and the output that is written
to the img (if at all). 
I think the most obvious problem is the cutOutInnerPolygons()
method that creates the thin areas which are later deformed by the filters. 
I will focus on that.

Ciao,
Gerd

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