[mkgmap-dev] Testing inter-tile routing with mapsource

Fri Feb 20 12:56:29 GMT 2009

Using maps generated with r915 I've spent a while trying to route to
places all over the UK. Places within my start tile work fine as expected.

Inter-tile routing works but I have the following observation

If you route to somewhere just inside the adjacent tile then the route
selected is usually fine. If you route to somewhere deep inside the
adjacent tile then the route chosen is far from optimal. It's as though
motorways are being avoided until you are out of your starting tile
after which the route takes the shortest path to a motorway and proceeds
as expected. This seems to happen if travelling North, South or East
(I'm not in a position to test West)

Similarly routing to places beyond adjacent tiles is not optimal but
presumably this is due to the above e.g. going from Manchester to
Taunton doesn't hit the M6 until near Stoke. After that it leaves the M5
north of Bristol, goes through the middle of Bristol and then rejoins
the M5 but this is near the NW corner of one tile and the SW corner of
another so I would expect oddities at this point.

The work that's been done so far on inter-tile routing is fantastic and
I don't want anyone to think I'm having a go I just thought the info
would be useful

Thanks

Paul

Mark Burton wrote:
> I have spent quite a while crawling around a 13 tile map using mapsource
> and, so far, I can route anywhere that's actually connected. N/S/E/W it doesn't
> seem to care.
> 
> Sometimes, it will just draw a straight line but if you break the route down
> into smaller pieces it can route.
> 
> It seems like that it's a complexity thing. It just gives up when it
> thinks the route is too tough to compute (computer says no).
> 
> Felix's point about the OSM data being not perfectly connected is
> interesting but we can't control how the gps behaves and we can't just
> go around linking up roads that look close enough to be connected but
> aren't actually. So I don't know if we can do much about that.
> 
> Cheers,
> 
> Mark
> 
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