[mkgmap-dev] shape merger in high-prec-coord branch

Wed Jan 15 20:06:02 GMT 2014

> Hi WanMil,
>
> WanMil wrote
>> The description of the algorithm sounds quite easy. I like it!
>> Maybe it could also be used to improve cutting in the Multipolygon class?
>> How do you avoid that two shapes connected with two edges and that
>> surround a hole are merged? I think many shapes cut by the
>> MultipolygonRelation have this characteristic.
>
> the trick is that the merge is done for one sub division. That means
> that I just have to make sure that the number of points < 250
> so that no further routine splits the shape.

Ah, that's the trick! Well done!

>
> It might be possible to move the merge higher up in the chain,
> for example after the clipping. In that case I have to make sure
> that I don't create shapes that PolygonSubdivSizeSplitterFilter would split.
>
> I know that this is a bit risky, but maybe I can get rid of all
> Java2DConverter methods that convert to double and back to int.
>
> Gerd
>

I am thinking about if it makes sense to add a kind of sudden merging in 
the multipolygon cut routines. The idea is as follows:
If the cut of an area returns more than 2 areas, two of the areas can 
safely be merged if their common edges (1 edge is the connection of two 
points) are all connected.

This would result in less cut artifacts. Maybe it is also possible to 
remove points synthetically added by the cut.

What do you think?

WanMil