h a l f b a k e r y"Look on my works, ye Mighty, and despair!"
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I was reading about inertial navigation systems the other day and
it
occurred to me that the iPad (and technicaly the iPhone and
iTouch
too) has all the hardware required to make such a system. It has
a
three axis accelerometer, gyro, and magnetometer compass. I
would love to see somebody
write an app that would take data
from these sensors, apply some relatively simple physics
calculations, and have it return a location, speed, and direction.
How would this be useful? Well, the GPS system is said to be
overtaxed as it is and might not last much longer. It is also
prone to
interruption by solar flares and Chinese missiles. I realize that
the
accuracy would never be good enough for an auto navigation
system, but it would be great for pilots who can cross-reference
the
printed latitude and longitude with a map to figure out where
they
are, within a couple miles. Also, it would be really really cool to
be able to navigate a cessna the same way as Apollo 11 :)
I checked around on the internet and there has been a little
discussion of this but mostly people just decide it's pointless
and/or
impossible (it isn't) and move on. I was about to write
this app myself and then I realized that you need a Mac to write
iOS apps and I don't have one of those.
Not the first time this link has appeared here I know... such a cool technology!
http://en.wikipedia...Inertial_navigation
[DIYMatt, Jan 17 2011]
Accelerometer in JavaScript
http://www.mobilexw...er-websockets-html5
Retrieve accelerometer data in Safari on iOS 4.2 [iaoth, Jan 18 2011]
[link]
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I don't know a single private pilot, nor have I ever heard of a private pilot, with inertial navigation. And as far as I can tell all of the apps in that link just use GPS. |
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My N900 has just accelerometers, and I tried writing a program that would integrate their output - I can tell you that it's horribly innacurate. |
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This isn't a new idea. This is the reason they stuck gyros and a compass in the newer smartphones. |
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The reason it isn't done is the "gyro" in your phone stinks compared to the gyro that Apollo used. The MEMS gyros in your phone are rate change gyros. They are fine for short time intervals, but suffer drift VERY quickly. Excellent write-ups on this an other issues are available if you look at the Lunar Lander competitions. They solved it by switching to EXPENSIVE laser gyros which are way more accurate but are still rate change gyros and still not as good as real gyros. The solution as anyone who owns a Wii with the little Motion Plus add-ons knows it to frequently correct for drift, by using the accelerometers to sense the direction of gravity and assume that is down. This doesn't work in an accelerating vehicle, so you will quickly loose your sense of direction. |
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In any case this project is being worked on by UAV software people, but all use correcting mechanisms to limit drift, some use IR sensors to optically sense the direction of Earth, others use the Earth's magnetic field, but ALL use GPS for error correction. |
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You don't need a Mac if you just want access to the
accelerometer data. See link. There's also a
geolocation API in JavaScript available since iPhone
OS 3.0. |
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I'm curious how the GPS system is supposed to be
"overtaxed", anyway. It's not a two-way system. |
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Satellites transmit data packets over and over. Receivers on the ground pick them up. Each satellite
transmits the same thing, regardless of there being
one receiver on the ground or one million receivers. |
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