

Paradise lost: SatNav "destroys" local knowledge - RiderOfGiraffes
http://news.bbc.co.uk/1/hi/magazine/8133890.stm

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RiderOfGiraffes
I submit this for a few reasons.

The first is that when I use SatNav I arrive at my destination having no real
idea where I am. I remember in a science fiction book reading a statement like
"We claim to have explored space, but in truth, we have explored the small
bubbles that surround individual planets. Of the great depths of true space we
have no knowledge." I feel a little like that now when driving longer
distances with the SatNav.

Secondly, it's interesting how often the SatNav produces "obviously" sub-
optimal routes. The Travelling Salesman Problem is well-known to be NP-
Complete, so it's not surprising, but some of the foibles are
incomprehensible. It's no wonder some people distrust them, and quite
surprising that others seem to have complete faith in them.

Finally, stop for a moment to consider the miracle that is the modern SatNav.
Despite its short-comings it contains a device to tell you where you are to
within a fathom, maps that know where you are and where you're going, enough
power to compute a sensible (if not always optimal!) route between the two, a
suer interface that non-technical people can usually drive, and all for the
cost of a few hours work.

Addendum: GPS works by computing varied flight times of radio pulses. Light
travels about a foot per nano-second, so a GPS receiver has to work with time
differences less than a typical clock cycle (for the on-board computer). If
you have a 1GHz computer, light cannot travel across the motherboard in a
single clock-cycle.

Stunning.

PS: Yes, I do know the details, and I know the inaccuracies in the above.

~~~
wlievens
What does the Traveling Salesman Problem have to do with typical GPS
navigation? Typical use of a GPS device involves a start and an end point, and
every once in a while a couple points in between, that ideally you may want in
optimal order (though I doubt typical devices can do that for you). But
there's nothing intractable about the scale of that.

~~~
RiderOfGiraffes
Sorry, you're right. My recent work has involved pathological cases of dynamic
spanning trees, and I've recently proved that a sub-class is NPC, and I mis-
spoke myself here. The SatNav problem is obviously easier. Given the power of
the processor, limited memory, and complexity of streets (in the places I
typically deal with) I still find it surprising.

But you're right. Dijkstra's algorithm clearly solves this problem simply
enough in _O((|E|+|V|) log |V|)_ for the sparse case.

Apologies.

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jcdreads
I think this is an interface design problem, not something intrinsic to GPS
navigation.

Provided that I set the unit to show my position on an always-north-facing
map, I arrive at my destination knowing _exactly_ where I am. If, by contrast,
I leave it in its default mode of rotating the map around an always-up-
pointing car, then I get completely confused.

I also never use the spoken directions, precisely because I want to know where
I'm to go, not when to perform atomic actions like turning; and the map shows
me where to go. If I need to get on I-93 N, and the map shows me as being near
I-93 N, then I'm smart enough to follow the signs and to reckon when to be in
which lane, which are more likely to be correct than the map in the GPS unit.

A constantly changing, map-like rendering of what I see out the windshield
accompanied by context-free commands is not helpful. A map that magically
shows me my current position and direction is.

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Luc
Pffft... GPS. All you need for navigation is a South-Pointing Chariot:
<http://odts.de/southptr/>

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yardie
I can't really complain about them. I used one this weekend and it saved me
from having to buy a very expensive train ticket. In normal instances the
shortest route between 2 points is a straight line. Which would have taken me
through a very busy downtown. The Satnav had me drive 5 minutes out of my way
to find an artery and saved me 30 minutes. I arrived at the station with 10
minutes left.

If I had chosen the logical route I might still be waiting for the next train.

Also, if you are in unfamiliar territory local knowledge is useless. And if
you are local then the navigation is barely useful.

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stcredzero
_The technology for sat-nav, in other words, was around for several years
before it was developed. All these different inventions simply needed to be
brought together._

The computer revolution hasn't happened yet. It's still in progress. In any
tech revolution, culture lags tech. Galois fields were around for well over a
century before we figured out the practical use for them. The electric arc was
discovered in 1802, and we still might find additional uses for it.
(Relatively low-tech high-impulse+thrust drives using electric arcs to
superheat hydrogen.)

