h a l f b a k e r yAssume a hemispherical cow.
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a digital camera that does the work of the old compass/map
and astrolab and solar tracker combined with a watch...... to
provide the best possible position fix and heading.
of course, this won't work in cloudy weather, but-----it will be
robust to not depending on a gps system.
gps systems
only work at certain latitudes, glonas and
european gps work at more northerly lattitudes. but when you
look at the globe------------civilian location tracking is rather
limited.
GPS performance standard
http://www.gps.gov/...rmance-standard.pdf
2008 version [lurch, Apr 24 2014]
Well, somebody had to do it..
fake_20astronomical...d_20to_20navigation
[not_morrison_rm, Apr 25 2014]
cart that always points...in some direction
http://en.wikipedia...th-pointing_chariot
[not_morrison_rm, Apr 25 2014]
[link]
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Have you been following innocentive.com? There was a contest requesting ideas like this. |
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Shouldn't be too hard to bake. I know there are
systems that can do this on military aircraft for
example but an app would be nice too. |
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The position of planets should allow the app to automatically figure out roughly what year and month it is (based on predicted positions for the next several hundred years), then based on the position of the moon, the day (and if is accurate enough), the time as well. That way when you loose track of the time you can still navigate. |
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Of course that does make it orders of magnitude more complicated than an app that can pattern match one constellation in each hemisphere and take an acceleropmeter reading angle. |
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Practical matters: what's the typical accuracy of cell phone accelerometers for measuring angle? If the accuracy is 1 degree, then your navigation can be accurate to about 70 miles. |
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How hard is it for a cell phone camera to take photos of stars? I think you might need a tripod and a long exposure time. I seem to remember it being somewhat tricky, even with a good quality camera. |
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//How hard is it for a cell phone camera to take
photos of stars?// |
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Harder than it is to phone someone up and ask them
where you are. |
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//gps systems only work at certain latitudes// What
evidence is there for that? |
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//but when you look at the globe------------civilian
location tracking is rather limited.// |
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I didn't even notice this the first time I read the idea,
but this is totally wrong. Civilians GPS navigation is
accurate down to centimeters where WAAS is
available and down to less than a meter over the
entire world. |
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what evidence is ther for gps availability? |
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do you even know how triangulation works? and
range and angles? gps for civilians is severely limited. |
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as for calling someone on a phone? UM NO ---you are
NOT USING any connectivity to establish location. |
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also, the military , darpa have already developed
chips for dead reckoning of location, that are
probably more accurate than this system, but that
technology is pretty far advanced using special
hardware. the solution i'm suggesting probably
doesn't need any sophisticated hardware..... |
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buchanan for someone who knows a bunch about
space----gps is something you should know about.
you should know the major players, glonass russia
european systems, us dod gps |
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//gps for civilians is severely limited.// do YOU
know anything about the GPS system? you seem to
think this is still 1992 when civilian access was
limited. My iphone will be able to find my position
down to the meter literally anywhere on earth, as
long as I have a clear view of the sky. I still bunned
this idea because I think celestial navigation with my
phone would be cool, and a good backup for the rare
occasions when GPS satellites break. |
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//what evidence is ther[e] for gps availability?// |
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Well, that would probably be from the US
Department of Defense's Global Positioning
System (GPS) Standard Positioning Service (SPS)
Performance standard <linked>. |
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In particular, on page 19, the coverage standard
per satellite is given as 100% coverage of the globe
(usable signal assumed to require 5 degrees
elevation above the local horizon, coverage to the
full globe less local blockages), and on the next
page, coverage standard per constellation is given
as 100% coverage of the globe. |
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In other words, every satellite participates in
providing coverage to every part of the Earth, and
as a whole, every part of the Earth receives
adequate coverage from satellites to provide
positioning at all times. That's the operational
standard the US DOD sets for the GPS system. |
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OK, you say they don't provide that standard of
service. Prove it. |
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(Degradation of GPS triangulation capability at
high latitudes is not from lack of coverage. It
comes from two sources - 1) Increased VDOP
(vertical dilution of position) because there are no
satellites near the local zenith for the solution,
and 2) the GPS receiver itself may not adequately
correct for the change in signal refraction in the
shallower ionosphere nearer the poles. This is a
highly speculative source of error - most
commercial gps units model ionospheric refraction
quite well.) |
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//an acceleropmeter reading// I think this is a more sophisticated type of sensor that compensates for little jiggles in a handheld device? |
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//Harder than it is to phone someone up and ask
them where you are.// |
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[AusCan531] - let's start with the basics.
Where's the last place you remember being?
Where are you supposed to be?
Do you recognize anything you see?
Are you drunk?
Do you have your clothes on? |
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I'm not sure I got those in the right order... |
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Hmm, I'm guessing that as a plan B, you could have an app with an accelerometer that does the "cart your you pull along that always points home" thingy linky. |
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//this won't work in cloudy weather, |
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There goes the UK sales. Hmm, gives me an idea. See linkette. |
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I have been thinking about the error in an accelerometer. I wonder if one could correct for this 1: correlatively or 2:iteratively. |
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For example: the app takes 1000 pictures of the sky. Predicted location is compared to GPS location. If there is a consistent and nonrandom directional error in the accelerometer, build in a fudge factor. Whenever GPS is available, use that to calibrate the accelerometer / astrolab prediction. |
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Suppose the error is random. Several thousand measurements should converge around the correct location. |
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Taking this further, it could be implemented as a fake. You open the app, it quietly finds your location from GPS, then photograps the sky, then looks up what it ought to find, then draws lines connecting the stars it thinks it can see and then announces "based on the stars I can see I think you are here". Should convince 99% of punters. Many users would still believe in it even if you used it on an overcast day. |
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If you're going to fake it, might as well fake a Viking
sunstone. |
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We got up to astrobabe on the other topic, it's probably a bad sign. |
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Nobody signs up Sandra Bullock, debris magnet... |
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I love it, lurch! My submission to the Innocentive contest was a device similar to that proposed here, but incorporating a polarised lens to serve as a sunstone. |
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I would like someone to weigh in on the concept of iteration to control for random error because of imprecise measurements. |
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/Practical matters: what's the typical accuracy of cell phone accelerometers for measuring angle? If the accuracy is 1 degree, then your navigation can be accurate to about 70 miles./ |
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Could one improve on this by taking multiple readings? |
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