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

Sun Jan 13 09:14:50 GMT 2013

> >
> > please check: the patch ignores preserved points, so I think it could break
> > routing.
> 
> You cannot route over polygons. So I don't expect that removing a point 
> from a polygon can break routing?

The filter is also used in MapBuilder.processLines()

> 
> > I would assume that straight lines are filtered by DouglasPeuckerFilter ?
> 
> Probably not. Otherwise the file size of the img files should have been 
> the same.

I don't understand. Your patch doesn't change the number of points 
on straigth lines, does it?

> 
> > (at least now that I've committed the removeShortArcs patch)
> > I did already look for other algos, eg. the VW algo
> > http://www2.dcs.hull.ac.uk/CISRG/publications/DPs/DP10/DP10.html
> > sounds like a possible alternative to DouglasPeucker.
> > On the other hand, I assume that the input for the filters will change
> > with the intended mp_cut changes, so we may end up solving the same problem
> > at two different places.
> 
> Yes and no. The mp_cut changes will only affect how polygons are cut 
> when they are part of a multipolygon. But there are many polygons that 
> are not.
> On the other hand I also use the algorithm of the RoundCoordsFilter in 
> the mp_cut branch (not yet committed) and therefore observe exactly the 
> same problems. So improving the RoundCoordsFilter algo will also solve 
> problems in the mp_cut branch.

OK. The RoundCoordsFilter really looks a bit brutal ;-)

Gerd

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