[mkgmap-dev] [PATCH] route recalculation sensitivity

Fri Apr 3 13:06:56 BST 2009

On Thu, Apr 02, 2009 at 11:53:07PM +0100, Mark Burton wrote:
> Had a chance to try out 0x110301 on a couple of bicycle rides and it
> appears to work OK on my etrex. The etrex recalculates after only a few
> tens of metres when I don't follow the route. I didn't spot it
> recalculating when it did not need to.

I took a bike trip today and can confirm this.

In a railway underpass, the signal was so weak that the Edge 705
recalculated.  Had the destination been 30 km away, this would have
"blindfolded" me for tens of seconds.  Not nice when you are in an unknown
neighbourhood.  This time, I knew the route and the recalculation (some
2 km distance) only took some seconds.

For what it is worth, the route near the tunnel has quite many turns:

* down the ramp (north), then turn 90 degrees left (west)
* ride through the tunnel http://www.openstreetmap.org/browse/way/25813501
* up the ramp (west), then turn 270 degrees left (north)

In the tunnel, the Garmin must have thought that I jumped to one of the
roads that run on the surface.  Back in Februray or so, when I was testing
a routable map, the device almost crashed in this tunnel when I was riding
the other way (southbound).  It didn't stop recording the track, but it
didn't display any map either until a power cycle.  I can't see anything
weird in the map data.

> I would have thought that changing to 0x110301 from 0xd0401 is probably
> worth doing anyway but as was suggested by some others, perhaps some
> further investigation would yield the "meaning" of those bits. I'm now
> quite busy with real work so I don't think I will be doing that.

If the meaning is ever deciphered, it might be better to reduce the
sensitivity a little bit, so that tunnels won't cause trouble.

	Marko