Hi Steve/anyone,
Can someone please clarify exactly how DivisionParser.round(Area) is supposed
to behave? My understanding is that it is taking the area passed in and
rounding
the edges *outwards* to the nearest multiple of 0x0800. ie, the area should
get a little bit bigger in each direction. If that is true, then I think
there are a couple of bugs in the rounding up code, especially when dealing
with negative values.
Here's the output from some logging I put into DivisionParser.getTotalArea():
details=(41.23698949813843,-73.50664615631104) to
(42.888779640197754,-69.93184089660645)
minLat=1d52f7
maxLat=1e7faa
minLon=ffcbba86
maxLon=ffce454c
Rounded bounds=(41.220703125,-73.564453125) to (42.890625,-69.9609375)
minLat=1d5000
maxLat=1e8000
minLon=ffcbb000
maxLon=ffce4000
As you can see, the min/max latitudes are both rounding 'outwards' and make
the area bigger, as does the min longitude (though I think it should go to
0xffcbb800 not 0xffcbb000). The max longitude is rounding the other way and
is making the area slightly smaller. This in turn leads to the following
assertion failure (when processing massachusetts.osm with default settings
and assertions enabled):
Found val=1dc1ce42 lon=ffce4200 left=ffcbb000 right=ffce4000
Exception in thread "main" java.lang.AssertionError: -3259904
at
uk.me.parabola.splitter.AreaSplitter.splitHoriz(AreaSplitter.java:101)
at uk.me.parabola.splitter.AreaSplitter.split(AreaSplitter.java:74)
at uk.me.parabola.splitter.Main.calculateAreas(Main.java:180)
at uk.me.parabola.splitter.Main.split(Main.java:95)
at uk.me.parabola.splitter.Main.main(Main.java:78)
Another potential corner-case is when rounding the value 0 down. Because
the check is for val > 0 rather than >= 0, it ends up being rounded down
to 0xfffff800 rather than just being left as 0. Is that intended (not that
I think that case matters so much)?
Assuming my understanding above is correct, here's how I think the rounding
methods should be implemented to give the correct rounding in all situations:
private int roundDown(int val) {
return val >> SHIFT << SHIFT;
}
private int roundUp(int val) {
return (val + (1 << SHIFT) - 1) >> SHIFT << SHIFT;
}
I've tested this change successfully with several files including
massachusetts.osm.
What do you think, is it the right thing to be doing?
Chris
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