[mkgmap-dev] [Patch] Improve boundary splitting

Sun May 6 19:56:48 BST 2012

Hi Gerd,

I decided not to include your patch.
The improvement is done only for the precompilation step. So it affects 
only a very few people that precompile the boundaries.
The patch itself adds another conversion step from Area to Shape format. 
In my point of view this is the breaking point where the source code 
will be no longer maintainable.

Before adding some special algorithms to improve performance it is 
necessary to overwork the boundary related classes and give them a clean 
structure. The current structure is the result of implementing a totally 
new function of mkgmap and improving and changing it completely for 
performance reasons (with a great result!). Now once it's working there 
is the time for some restructuring.

Sorry for that! I hope you understand my reasons.

WanMil

> Hi WanMil,
>
> attached is a patch that uses an optimized implementation of the
> Sutherland-Hodgman algorithm
>
> http://en.wikipedia.org/wiki/Sutherland-Hodgeman wikipedia
>
>
> which is much faster than the area.intersect. It is only used to create the
> precompiled boundaries.
>
> The improvements depend on the continent, for africa I see  130 secs with
> r2272 and 84 secs
> with the patched version. For asia, I see only a small improvement of ~ 10%
>
> On my machine, the precompilation of the boundaries is now quite often
> waiting for the disk.
>
> http://gis.19327.n5.nabble.com/file/n5670294/BoundarySplitter.patch
> BoundarySplitter.patch
>
> Gerd
>
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