111–120 of 191 posts
Earlier quoted context omitted.
It also has the potential to greatly increase the accuracy of the instant pace, which is a lot more volatile than the total distance
I mean, how erratically are you running? My pace wouldn't vary much over a typical 200m.
15cm GPS accuracy has been available commercially since about 2002. Trimble and Novatel both sold units. But you had to get a subscription to a service which had a network of ground stations measuring propagation errors through the atmosphere. The correction signals came in from a geosync satellite. You also had to be able to see about five satellites.
Wow, it's within a few cm. I wonder if Google Maps and those guys actually move the buildings around due to seismic events?
Earlier quoted context omitted.
>The military has better precision, only because they buy better hardware. That's not true. Military receivers can use the Y Code which is encrypted for military use only. There are some really fancy civilian receivers out there that can leverage Y code to a limited extent without knowing the encryption key but full accuracy is only possible on a military receiver that can decrypt and use the Y code.
By the way, has anybody tried to crack P(Y) code using a kind of "rainbow table"? (I'm not advocating that ofc, just curious...) I mean, it gets it's security because the parameters to its generating function are not known. But the function repeats after about a week, and presumely can't be changed due to the large numbers of legacy devices in the field. So you could just record the whole signal for a week (I did a b…
Semi-codeless receivers can use it anyways. The reason is that the W code has a much lower data-rate (500KHz I think).
Take the incoming signal, correlate with the aligned P code. The resulting signal will be a MHZ wide signal, bandpass to it, and square the result. The squaring wipes off the residual W code. Because you bandpass filtered before the squaring you don't get so much squaring loss. Lock the resulting carrier, and use RTK signals and long observations to resolve integer ambiguities.
For a dual frequency rx you can exploit that P(Y) is the same on both frequencies and correlate them against each other to find the ionospheric delays.
Wow, it's within a few cm. I wonder if Google Maps and those guys actually move the buildings around due to seismic events?
Earlier quoted context omitted.
Copenhagen Suborbitals has a blog-post about those limits: By default all GPS units have some built-in limits (so-called COCOM limits) that prevents them from providing any data if the velocity exceeds 515 m/s at altitudes above 18 km. These artificial limits are built into GPS receivers to prevent bad guys from using them in missiles and other nasty stuff. ... and proceed to figure out a way around ... https://copen…
> to prevent bad guys from using them in missiles and other nasty stuff I was confused. So here's a translation: Bad guys = US enemies or non-allies. Not bad guys in any moral sense.
Or at least that's how I always understood it.
Why was "oil and gas exploration" an early adopter here? Can anyone connect the dots for me? I wouldn't expect interesting oil/gas pockets to have <5m lateral diameter, but then again I know very little about that industry.
There's a ton of money in oil/gas, and any technology that can give a slight edge is often worth it. For example, oil and gas companies were some of the first to use Iridium (worldwide satellite internet at ridiculous prices), and I'd bet that they are the biggest users of the Iridium network to this day. This goes for inventions in tons of fields.
For example, new breakthrough in diving: great, you can use that to work on underwater parts of drilling rigs. New breakthrough in robotics? Great, you can replace the expensive and dangerous dive crews with underwater ROVs. New breakthrough in geology? Cool, you can use it to find oil.
If anyone works in the field, I'd be interested in how this dual signal (L1/L5) chip interacts with the RTK/CPGPS [1] (which improves accuracy down to 1-3cm already (at the cost of using multiple GPS units)). RTK is commonly used in survey drones, and kits are available for about $1K. [1] https://en.wikipedia.org/wiki/Real_Time_Kinematic
RTK uses a fixed base station, ideally you know exactly where it is so that you know the exact location of your mobile unit (else you will at least get a pretty good relative position). With the new chips, Broadcom, u-blox and others are bringing to market now you are no longer dependend on a base station to get cm-level accuracy. Instead they exploit the different properties of the L1/L5 frequencies to infer stuff a…
Earlier quoted context omitted.
>The military has better precision, only because they buy better hardware. That's not true. Military receivers can use the Y Code which is encrypted for military use only. There are some really fancy civilian receivers out there that can leverage Y code to a limited extent without knowing the encryption key but full accuracy is only possible on a military receiver that can decrypt and use the Y code.
is there any reason to be even more accurate than a 5 meter radius? I mean, if you are targeting a person in a building, i can't see why it has to be more accurate than that. Navigation of a drone that is less than 5 meters in size may require higher accuracy, i suppose...
Earlier quoted context omitted.
>The military has better precision, only because they buy better hardware. That's not true. Military receivers can use the Y Code which is encrypted for military use only. There are some really fancy civilian receivers out there that can leverage Y code to a limited extent without knowing the encryption key but full accuracy is only possible on a military receiver that can decrypt and use the Y code.
is there any reason to be even more accurate than a 5 meter radius? I mean, if you are targeting a person in a building, i can't see why it has to be more accurate than that. Navigation of a drone that is less than 5 meters in size may require higher accuracy, i suppose...