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The vehicle correlates elevation raises and drops
measured
against their location via due north to create yet another
metric to navigate with.
So the unit takes a sample, it's at 25 feet above sea
level.
After driving 2 minutes at 60 miles per hour north plus 23
degrees it's now at 48
feet above sea level.
By the time you have a 4th or 5th
sample you've drawn a pretty distinct terrain pattern and
can
make a pretty good assumption of where you are.
This can be done with barometric pressure readings or
accelerometers measuring up and down motion the same
as exercise wrist bands telling you if you've gone up or
down stairs.
[link]
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You're going to need some pretty sensitive altimetry to pinpoint your height to within, say, 10 feet. If you use a pressure-based altimeter, the variation due to barometric variations will be way bigger than that. |
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Of course, you could always get your height from the GPS... |
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Yes, but the relative elevations between 3 or 4
points
wouldn't change due to weather conditions and
that's
what you'd be measuring. |
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Even apparently flat
landscape is pretty lumpy and it's sort of like Earth
fingerprints. You get a big enough group of sample
points with a particular compass location it's a
pretty safe bet you'd know where you were. |
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I think electronic barometers are pretty sensitive. |
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But fine, measure the variation between points
with accelerometers which is how I think they have
those exercise measurement wristbands tell if
you're going up the stairs. |
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So here's how it words. You're driving from point A
to point B and you turn this thing on. It says "Ok,
you're at level X." Let's start measuring your up and
down / speed / compass location and draw a 3d
line. Doesn't matter what the starting elevation is.
It says: "Compass location Y, 60 miles per hour to
Y1 after 5 minutes elevation is X+2, after 5 more
minutes Y2, X-4," etc till you have a nice little
unique picture of this particular path, you compare
that 3d path to the 3d paths in the database and
find your location. |
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I suppose you could even measure tilt of the
vehicle. Tilted down 2 degrees and drove for 5
minutes then tilted up 5 degrees for 3 minutes etc. |
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So yea, barometer might be a bit sketchy but there
are plenty of other ways you could do this. |
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Relative altitude? Just measuring the car going up and down? Ah, I get it. Big potholes. |
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It's all about the potholes, I tell you! |
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Hang on. You'd need a correction factor as global warming -> sea level rise, and everything's height is measured against sea level. |
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Also there's an upper limit, as according to my calculations on the 22nd of January 2089 - at about tea-time - the very tip of Mt Everest will be finally and permanently under the waves. |
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And then where will be, eh eh? Tell me that! |
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I'm steering more towards the "angle of car / attitude
determined by accelerometer / speed calculation /
relationship to due north /" model as being
impervious to such issues as apocalyptic weather
changes and such. |
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That being said, by the time Mt Everest is under
water all my designs
are no longer under warranty, expressed or implied. |
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//You'd need a correction factor as global warming -> sea level rise// |
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I believe the factor is 3.3mm per year, and has been since 1880 (and probably before that). The sea is smarter than we give it credit for: it started rising in anticipation of anthropogenic CO2 emissions. |
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