Originally Posted by ACCORDKID

HOLY COLLEGE COURSES BATMAN!

whatever you do for a living i hope you make a lot of money. i was litteraly laughing reading that because of the technicality of what you said. but well put.

Originally Posted by Fabrik8

I'm just a hopeless nerd like that. I'm back in school, finally getting a degree at 31. And I'm broke because of it. Trust me, knowledge and money don't always go together..

Originally Posted by Brock Obama

LOL

The real number is classified.

Originally Posted by Fabrik8

Normal, fairly constant speed isn't that hard, it's an sampled average vs. time, so if your speed isn't rapidly changing, it can pretty well calculated from the GPS position. Rapid changes in speed are hard because the calculations either have to wait for the next GPS position and until then use dead reckoning based on the derivative of the speed (which is acceleration). Also, by the time the GPS position is calculated, you're not there anymore and you're moving at a non-constant speed.

Help, I can't shut my brain off.
Your speed is a vector, and so is your position. But vectors are straight lines, so when you reach the next datapoint, you may not be going that same speed, and you may not have traveled on a straight line. So at that next datapoint you aren't where the software thought you'd be. All of these things add up to a lot of guessing, which is a lot of cumulative error (most of which is compensated, but that has error too), and then add in the position error, etc..



1/4 mile accuracy gets worse because the position of the GPS isn't generally good for more than about 15 meters, which is roughly 50 feet. This could also be as good as 1 to 5 meters, but how do you actually know what the accuracy is at any given time or position when you're moving?
So that's +/-50 feet where you're starting, and +/-50 feet where you end. So it could be up to +/-100 ft off of a 1/4 mile, plus the obvious speed error too. SO every time you get a datapoint from the GPS, the software tries to correct what it guessed based on what it now knows. But what it now knows has some error..

I'll just end this boring lesson by saying that even if your software is perfect, you can still only be as good as the hardware, and that's limited by the global system. If we could use the military GPS data, then you could get position down to about 30 cm (that was the last I heard; might have changed).

Can you tell I used to have to interface with (aftermarket) GPS hardware at a former employer?

Originally Posted by tangoDelta

No, its not. This information is taught to many service members, including those without security clearances. It is also available on the internet from many different sources.

The PLGR is a very commonly used military GPS system so lets try that one out.

ftp://ftp-fc.sc.egov.usda.gov/NE/Out...plgrappx_c.pdf - States < 1 meter accuracy.


http://www.ion.org/museum/files/PLGR-9~1.PDF - States < 1 meter accuracy.


If its good enough for a M198 then its good enough for me! The key (no pun intended) is to have the crypto-key, otherwise the PLGR, DAGR and any other military used GPS only has the accuracy of a civilian GPS. None of this is OPSEC so don't try to nail me on that one