[mkgmap-dev] patch to write polygons in decreasing order

Mon Nov 7 22:24:22 GMT 2016

Hi Gerd

I've been looking at ShapeSplitter and clipping to a rectangle
algorithms generally. I don't feel I know enough about how to use the
java.awt.geom package to implement this effectively, and so I'd rather
keep to using Java2DConverter and .intersect(), even though it is most
likely much less efficient.

Ticker

On Sat, 2016-11-05 at 23:33 -0700, Gerd Petermann wrote:
> Hi Ticker,
> 
> Gerd Petermann wrote
> > Alternative would be to implement a clipper which doesn't need
> > area.intersect(). I've once coded the "Sutherland-Hodgman
> > algorithm" but
> > ways or concave shapes producing spikes, but I still think this
> > would be a
> > great improvement. See attached (out-aged) patch and the wiki
> > https://en.wikipedia.org/wiki/Sutherland%E2%80%93Hodgman_algorithm
> > for further details.
> 
> I just noticed that the algo is already used in
> ShapeSplitter.clipSinglePathWithSutherlandHodgman(),
> the comment says
> "Clip a single path with a given rectangle using the Sutherland
> -Hodgman
> algorithm. This is much faster compared to the area.intersect method,
> but
> may create dangling edges." 
> I think these danling edges are now removed in the
> RemoveObsoletePointsFilter, so maybe it is worth 
> trying. 
> 
> Gerd
> 
> 
> 
> 
> --
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> -write-polygons-in-decreasing-order-tp5884038p5885439.html
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