[mkgmap-dev] Question regarding overlap in splitter and mkgmap

Sun Oct 28 19:02:20 GMT 2012

> Hi,
>
> I am again working on an algorithm for splitter that detects all incomplete
> ways and rels.
> It works fine with input like finland.osm.pbf (~100MB) and -Xmx1000M, but it
> probably would fail
> to process europe on a 32bit machine.
> Up to now, we use the overlap value to reduce the likelyhood of incomplete
> ways and rels.
> Now, I wonder what exactly splitter should do with a way that has only
> points in this overlap.
> To make it easier, let's assume that this way is not a member of a relation.
> Is such a way used in mkgmap or is completely ignored?

AFAIK yes - it's completely ignored.

> If it is completely ignored, I think splitter should not to write it, else
> it should try to
> write it with all nodes.

Yes, that would be great. It would avoid a lot of problems with 
incomplete multipolygons.

>
> In other words: If splitter could make sure that every way and relation that
> a) has a node within the real bbox
> b) may enclose the real bbox
> c) may cross the real bbox
> is written to the tile with all related elements (nodes of ways, members of
> relations),
> would we still need the overlap?

I think the overlap is superfluous if splitter can guarantee a) to c).

If splitter can handle a) to c) you will have the complete country 
boundaries in each tile. Not a problem for Luxembourg but maybe in 
Russia, Canada or similar big states it will blow up each tile. Maybe 
this growth is worthy to check once during your development.

> I remember an algorithm in mkgmap that searches the nearest city. Would this
> algorithm "see"
> a city that is in the overlap ?

No, this algorithm runs after all elements have been cut to the bbox.

>
> ciao,
> Gerd
>

If you manage to implement that you will solve a long outstanding 
problem of splitter/mkgmap so I cross my fingers that you are successful!

WanMil