[mkgmap-dev] bugreport for new splitter

Mon Aug 10 10:52:35 BST 2009

Hey Steve

> OK, if that is the case I was thinking that the overlap might be
> better as a percentage of the size of the area.  In areas where there
> is a straight road that continues for miles and miles nodes might be
> widely spaced, but that is unlikely in densely mapped areas.

Makes some sense, though I don't suppose we'll know what it affects until 
we try. My suspicion is that it will introduce other problems (like dropping 
too many overlap nodes from just outside dense areas, or including far too 
many overlap nodes in a sparse area if a dense area falls just outside it). 
And even with a percentage based approach it is still possible (though less 
likely?) to see this problem.

If I implement special handling for 5+ areas per node as described (perhaps 
with an upper limit/warning on the number of these special nodes) the problem 
goes away anyway.

Another option might be to set the overlap in each of the 4 directions to 
Math.min(2000, smallestAdjacentTile<Width|Height> / 2 - delta). That should 
ensure a node can't fall into more than 4 areas.

> The Garmin units have different sizes depending on direction and
> latitude, but 2000 is over 4km(?) and that might be too much in any
> circumstances.

Given that it's only when a relatively low number is given for --max-nodes 
that we run into any trouble, maybe it's best to leave at 2000 for now. Is 
there a reason why people would want to use such a low number? Smaller tiles 
so more flexibility about exactly what they upload to their Garmin perhaps?

>> Here's an example of a node that wants to be in 5 areas:
>> 
>> <node id="447665000" lat="46.0753181" lon="13.1930056" version="1"
>> 
> That is an interesting area, as it appears that buildings are mapped
> so there is a much higher node density than normal, but only the main
> roads are there.

Yeah I saw that (and compared the area with what Google maps has). I suppose 
someone traced the buildings off some other source but not the streets for 
whatever reason.

Chris