Arguing with the SatNav

One of the things I did when I sorted out my laptop at the weekend was update the supporting software for my various Garmin GPS units. There were a couple of updates for my little StreetPilot i2, the first being an improved quality British voice for the unit – which does sound slightly different – and then one of the regular software updates.

Driving to and from the Wrexham area I noticed that one of the changes seemed to be that the unit was a lot more keen for you to follow it’s route than before. If that sounds a bit odd, I’ll explain.

If you’re heading anywhere north from here, the SatNav units and route planners will invariably go for the A34 from Newbury to Oxford heading onto the M40, then will always take the northern route around Birmingham, taking the M42 and M6. However I’d never consider using the A34 thanks to it being two lane all the way and congested with lorries heading north from the south coast ports, and will instead usually take the A404 and join the M40. Although slightly longer in terms of distance, being three lanes there are less delays with lorries. I’ll also tend to take the southern route around Birmingham too.

Coming back south today, I took my usual route, and carried on along the M40 at the A34 turn off. In the past the SatNav has usually switched to my usual route – the difference in time is minutes at most, but after this software update it appears to do things slightly differently. Instead it tried to take me around the south side of the Oxford ring-road, adding a good ten to fifteen minutes to the end time. As I again went past that turn it recalculated again and went for my normal route, and with a much lower finish time.

It’s fairly obvious that the system is not recalculating a full route when it recalculates, the primary reason I’m sure being speed. Most SatNav’s will not search every possible route between two points – the techniques they use to prune the search tree and to determine which routes are not worth searching are obviously the thing that differentiates the performance – check out this recent article comparing the routing engine performance of the three major brands for some examples. Anyway, what the latest update appears to be doing is trying to first guide you back onto it’s existing route. Thinking of some of the other points on the trip where I diverged, for example when I came off the M40 a couple of junctions early to enjoy the back road route home – great fun as long as you don’t get stuck behind a tractor – it doesn’t seem to do a full recalculate and is making much more effort to turn you around than it did before. Considering that by this point on the trip the SatNav is only really on to keep track of the safety cameras it’s a bit annoying that it starts arguing with the way I’m going!

Thinking about this, perhaps the ultimate improvement to a SatNav system would be one that learns. For example my back route home from the M40 is only a few minutes longer, and is a route I quite often take as thanks to the tank being pretty empty, and the car nicely warmed up it is a nice antidote to the usually miles of motorway cruising I’ve been doing – the ultimate system would remember previous patterns and not, as it did today suggest two routes to get me back to the motorway before finally fully recalculating.

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