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

Sun Jan 13 05:49:55 GMT 2013

WanMil wrote
> 2nd change: The RoundCoordsFilter does not care if an area is rounded to 
> a line which happens quite often. The patch tries to remove the line
> parts.

please check: the patch ignores preserved points, so I think it could break
routing.

WanMil wrote
> Anyhow I think there is more improvement possible. I have attached two 
> gpx files. Bye the way the patch contains some commented lines that 
> creates the GPX files for each polygon treated by the patch. 
> 11315_16_org.gpx is the input polygon to the RoundCoordsFilter and 
> 11315_16.gpx is the result (using the patch).
> 
> Some possible improvements:
> * Straight lines sometimes contain more that one point and it should be 
> easily possible to remove these additional points.
> * The filtered polygon sometimes still contains lines which are not 
> removed by patch because the overlapping lines do not contain the same 
> points. You can see this in the attached gpx in the upper middle of the 
> right polygon block.
> * The filtered polygon could be simplified and sometimes split into more 
> separate polygons which are now connected by a line.
> * Better resolution dependend filtering?

I would assume that straight lines are filtered by DouglasPeuckerFilter ?
(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. 

Gerd

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