h a l f b a k e r yWarm and Fussy
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Just as the vikings used a sunstone, presumably modern
phone or drone cameras could have multi-spectral sensors. |
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The notion of using imagery versus an image database (plus
gyroscopic inertia) does address clouds to some extent. |
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A truly hybrid navigation system (one that for instance
seamlessly uses cell tower triangulation, wifi routers with
known addresses, etc), would be quite resilient |
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Along with accelerometers, could we not build a GPS using magnetoreception to navigate the way that migrating birds do? |
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So, sort of "compass" type of thing? |
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Not a 'pole' detector, a field line proximity detector. |
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Why not just stay where you are ? |
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How do you get to Google Earth in the middle of the ocean
without a satellite? |
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1. Inflate airbed on beach. |
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2. Walk into sea carrying airbed. |
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well, you could have it on CD, simple enough, [pashute] :) |
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I was discussing GPS satellites, not all satellites. |
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//Not a 'pole' detector, a field line proximity detector.// |
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Sounds a lot like a dip compass, which aligns with the local field and tells you the local magnetic dip angle. |
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Fascinating. Never heard of a dip compass before.
I had assumed that the Earth's magnetic field lines were more uniform, after all the migrating wedges of Canadian Geese zig-zag as they migrate as though feeling individual lines, so I had also assumed that it would be possible to tell when crossing one latitudinally. |
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Bit of a snarled mess though isn't it? |
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Yes. And they're dynamic; the drift is rapid enough to make them useless as a navigational tool, primarily because it's not accurately predictable. |
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The chaotic* nature of the field means that aliasing is commonplace - not what's needed. If a navigational method yields, for example, three possible solutions, then this can often be resolved by reference to other factors, but where there are a dozen or more scattered in the same general area, it's useless. |
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*In the strict mathematical sense. |
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// I had also assumed that it would be possible to tell when crossing one latitudinally.// Uh, you do know that a field line is not actually a line? |
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But anyway, the general trend is for the field to align northish-southish, and to be horizontal at the equator whilst dipping down into the poles. But locally it's much more chaotic - basically a mess. |
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You can navigate pretty precisely if you have a good compass and dip-compass, and an up-to-date magnetic map. |
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Sturton (and this is, of course, completely irrelevant) navigates using alcomancy. Basically, he can tell how far he is from a pub in any given direction; triangulation and a comprehensive internal map of pubs allow him to pinpoint himself to within about 20 metres across most of the UK. |
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Of course, finding a pub that he hasn't been barred from for life is a little more of a challenge. |
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//Uh, you do know that a field line is not actually a line?// |
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I did not know that for myself no.
When looking at a magnetic field through a ferrocell or in home experiments, (my daughter got me a ferrous sand hourglass with a magnetic base and I've been playing with it), the filed lines seem well defined while turning a magnet.
Linear peaks and troughs at least. |
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If you put iron filings on or near a magnet (which I'm guessing is similar to your setup), they tend to form discrete chains or lines. But that is because of the way the individual filings distort and respond to the field. |
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The first filing to stick to the magnet acts as a little spike, concentrating the field around its tip. That, in turn, causes another filing to join it, which does the same thing again, and so on. So, the filings naturally "crystallize" into chains. Conversely, there's a weak repulsive force induced between adjacent chains, so they space themselves out. It's not the case that the magnet produces discrete "field lines". |
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If you take a single piece of iron (or a magnetometer or any other instrument that responds to a magnetic field), and move it around near a magnet, you will find that the field changes continuously, not discretely. |
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GPS is an acronym. Who knew |
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If you precisely arrange a phone so that it casts a
shadow on a pre-marked piece of paper, the phone
could use the camera, time and internal compass to
work out longitude and latitude.
Of course, if it is dark, the camera cannot see the
shadow.The built in LED flash-light solves this
problem. |
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It's that sort of genius thinking that's made Belgium what it is today ... |
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Baked: celestial navigation systems on satellites themselves
as well as aircraft astro-inertial nav systems, ala SR-71. |
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I think what you have invented is automatic celestial
navigation <link>. The SR71 had it, because it was high
enough to have untroubled access to star light, and fast
enough that they went 'round and 'round relatively quickly.
I've heard mention by exRAF V bomber pilots that there was
supposed to be an equivalent device that "never worked".
Probably cloud. |
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matt, you beat me to it! any idea how they worked? I'm at
a total loss as to how this could be done without digital
imaging and computing. |
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ICBM's use celestial navigation at apogee for course
correction because it's independent of the vulnerable GPS
networks. Must be pretty good too - Trident D5 has a CEP
of ~90m and uses celestial navigation correction at
separation. It must be extremely accurate to do that. |
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...But I'm pretty sure ICBM and SR71 celestial systems are
only suited to operation above most of the atmosphere.
Not sure how well you'd go down here amongst the dirt
and smog. |
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I reckon you could do a lot however. A very accurate
true (Rotational) south (within a couple seconds of arc,
accurate enough to set up a telescope for timelapse
photos) can be found anywhere in the southern
hemisphere where the southern cross and the pointers
are in view, although that's only 50% of the time of
course. I'm sure there are other bright stars that can be
reliably seen through light cloud, etc - of course you'll
need to know the time to within a good accuracy. It
would be fun to work on the algorithm... |
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I wonder if you could win one or more of the possibly now
expired longitude awards/prizes? |
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Wonder if frequencies other than visible reliably make it through cloud cover. |
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// could we not build a GPS using magnetoreception to navigate the way that migrating birds do? |
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It's probably just me, but that seems a bit ambiguous? I don't think avian tool-use is quite up to it. |
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Yes, the bubble I've lived in is popping very slowly... and by degrees. |
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We have been experiencing technical difficulties and apologise for any current or future inconvenience this may cause as internal systems are recalibrated/ upgraded for optimal efficiency.
Fry-Co thanks you in advance for your patience.
Normal operations will resume as soon as public safety issues are resolved. |
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hmm, it turns out DIY radioastronomy is a thing. It also
turns out that its fairly easy to spot the galactic plane.
Depending on the frequency used, cloud shouldn't be a
problem and using a couple of well chosen reference
frequencies you should be able to to pull out a signature of
the galactic plane and kind of overlay them for certainty.
Then, as it's well mapped and its movement known you
should be able to derive a couple of points at either end of
the night sky. Should be useful enough to navigate by. Big-
ish antenna though. |
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Everything now seems to be 'cloud'-based so maybe
this should be a system based on looking up at the
sky and comparing the shapes of clouds seen from your
location with their shapes seen from other people's
locations and determining your location based on this
comparison. |
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//looking up at the sky and comparing the shapes of clouds
seen from your location with their shapes seen from other
people's locations and determining your location based on
this comparison// |
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While I think I am in Philadelphia, the clouds appear
uniform and grey horizon to horizon. So I deduce that the
city I am in is actually Manchester, UK. Good to know,
might get a curry later. |
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// Everything now seems to be 'cloud'-based // |
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//It also turns out that its fairly easy to spot the galactic plane.// You can generally hear them going over. |
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