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[mkgmap-dev] Bug in LocationHook?

From WanMil wmgcnfg at web.de on Sun Jan 8 21:17:25 GMT 2012

> Hi WanMil
>  > I remember that I tried the other strategy. I don't remember how I did
>  > organize the boundaries. But it was *magnitudes* slower (not just slower
>  > but magnitudes slower) so that I didn't started to improve my poor
>  > implementation.
>  >
> I tried it anyway and found some interesting results:
> Sometimes it is ~ 20% faster, sometimes it is much slower (maybe 100% ).
> So, I think it might be a good alternative if we can avoid the bad cases.
> I created a simple grid that stores all boundaries that intersect with
> each element (similar to the grid in splitter). This is done quicker
> than the creation of the quadtree.
> Using the grid, for each Coord I get a list of boundaries to test:
> ...
> Boundary b = currentBoundaries.get(blist.get(i));
> if (b.getBbox().contains(co)){
> if (b.getArea().contains(co.getLongitude(),co.getLatitude())){
> return b; // return the area that contains the point }
> }
> ...
> the performance problem is in the b.getArea().contains(...)
> For some boundaries, this test performs very slowly (> 1ms for one
> test), and it seems to be related to the number of points that form the
> shape of the boundary.
> Some areas are built with < 20 points, others with > 8000.
> So, what I need is a quicker contains() or some kind of tree that allows
> to avoid it.
> Any idea?

I think the problem does not exist in the current quad tree because the 
areas are splitted into subareas. This also reduces the number of points 
and makes it quicker and easier to test. You could get the number of 
points from the boundary and decide if an area should be splitted into 
subareas. It would also be possible to save the splitted subareas as 
precompiled bounds. If your grid always have the same dimension this 
might improve the handling.

You might also remove the merge step. For most tiles more than one 
precompiled file is loaded. The bounds are merged afterwards. This step 
sounds superfluous as the LocationHook only checks if one point of a way 
is in the boundary and not for all points. Therefore it is not necessary 
to have the boundary area as one complete area object.


> Ciao,
> Gerd
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