11 ms·

With functioning clocks, Galileo is accurate to within a metre, according to this article. That's crazy - I had no idea it was that accurate.

by jblok 10y ago

digi_owl 10y ago
Apparently they wanted to make it even more accurate, but got pushback from USA before they feared it would be used by hostile forces.
- Klathmon 10y ago
  What's the fear with more accuracy? From my (completely layman) perspective once you've got a meter or so of accuracy, you've got what you need for weapons. What's further accuracy get you that some nations are against everyone having?
  - nathancahill 10y ago
    A similar thing happens with commercial imagery satellites. Companies are forced to downsample their high resolution govt-only images to 30cm for the general public.
    - deleted 10y ago
      [deleted]
    - blackaspen 10y ago
      My understanding is that it's not exactly "by force" but rather a condition of funding. The U.S. Government is probably Digital Globe's largest customer.
      - blackguardx 10y ago
        No, it is by force. It is similar to ITAR regulations. If you break that rule, your management team is probably going to jail. It would be akin to spying for a foreign power. Source: I used to do some consulting for a satellite imagery company.
    - maxerickson 10y ago
      That's slightly different though, better imagery makes it possible to resolve more features. With the improved positional accuracy it's a 2 meter circle vs a 1 meter circle. What tactics does a 1 meter circle enable that the 2 meter circle does not enable? Also, DigitalGlobe only has 30 cm capability: https://en.wikipedia.org/wiki/WorldView-4 https://en.wikipedia.org/wiki/WorldView-4 Who is downsampling (DigitalGlobe/GeoEye was downsampling earlier 40 cm imagery for Google, to 50cm)?
  - michaelt 10y ago
    There's no fear about accuracy - the plan is that Galileo will charge for high precision services. Indeed, you can buy centimeter-precision GPS services right now for applications like surveying and precision farming [1] - those are small markets, of course; self-driving cars are the real prize. The objection from the US amounted to the fact an early Galileo design would have reduced their ability to degrade satellite navigation in war zones. Later the design was changed, so the US can jam Galileo - which avoids the US objection, but makes Galileo less useful as a backup. [1] http://www.trimble.com/Positioning-Services/Trimble-RTX.aspx http://www.trimble.com/Positioning-Services/Trimble-RTX.aspx
- madez 10y ago
  I'm very disappointed that the EU bowed to their demands. It is the second clear sign I know that Europe dances to the USA's pipe; the other one was the grounding of the bolivian presidents plane in 2013. I hope that Europe eventually stops giving in to demands by the USA. [0] https://en.wikipedia.org/wiki/Evo_Morales_grounding_incident https://en.wikipedia.org/wiki/Evo_Morales_grounding_incident
  - trimbo 10y ago
    Or maybe the European team simply agreed with the concern?
    - madez 10y ago
      Now, that is a valid concern. So far the first I read. Maybe some countries in Europe also wanted to see Snowden catched.
      - dogma1138 10y ago
        You do understand that the security concerns of Europe and the US are mostly overlapping right?
        madez 10y ago
        Exactly, mostly. I think Europe should have efficient and effective measures to ensure it's safety also when they don't align.
    - dmichulke 10y ago
      Would there be a reason why GPS with 10m accuracy is OK but Galileo with 1m is not?
      - nickpsecurity 10y ago
        GPS has better than 10m accuracy in another operating mode. Only the military is allowed to use that one, though. Then they don't want Galileo being 1m accurate? Probably same military reasons.
- drzaiusapelord 10y ago
  This is actually untrue. The US didn't like that the EU was using bands close to GPS so if there was a conflict where the Russians or Chinese were using Galileo to target American troops, the US would have no choice but to shoot down or otherwise disable Galileo satellites by force. No one wants this, so the EU chose a different frequency that could be jammed without jamming GPS. Accuracy was never a concern. Galileo can't do better than a meter for many reasons, not the least of which is number of satellites, clock accuracy, and cost. https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)#Tension_with_the_United_States https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)...
  - madez 10y ago
    Then Europe should treat shooting down of Galileo satellites as an act of war and react as such. It's not Europes business to make it easy for the USA to wage war.
    - drzaiusapelord 10y ago
      Europe is part of NATO and has major incentives to cooperate with the US. In the scenario where the US would have to shoot down Galileo sats, would most likely be one where the US is protecting Europe from China or Russia as we're talking WWIII. I imagine this little story is little more than a tempest in a teapot designed to enrage Euro nationalists. The reality is that when you're in a shared defense agreement, your weapons systems, including nav systems, need a high level of cooperation. A frequency shift isn't the tragedy you're making it out to be.
      - madez 10y ago
        In the scenario you mentioned Europe could turn off Galileo if deemed necessary, no need for the USA to shoot it down. The solution taken just makes it easier for USA to wage war against Europes interests.
        drzaiusapelord 10y ago
athenot 10y ago
With India, China and Russia launching their own positionning systems, I wonder if it would be possible to interpolate an even higher precision by listening to all 5 signals at the same time. (I don't know enough about signal processing to know if that's a possibility or not.)
- ekimekim 10y ago
  (warning: armchair expert, I've just read a bunch of wikipedia pages) I believe there's still sources of systemic error that would affect all the signals similarly, such as atmospheric interference, so even taking (for example) the average of the reported position from all the services may not improve accuracy that much. https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_... is a good read.
  - maxerickson 10y ago
    The typical approach seems to be to consider all the visible satellites together (rather than solving for the position indicated by each constellation and averaging them). So in practice having more satellites means that a good position measurement is possible more of the time.
  - kittenmittens 10y ago
    You can also reduce some of the atmospheric interference by modeling it using both the L1 and L2 signal.
- jessriedel 10y ago
  Not only is it possible, it's already done in many (most?) smartphones made over the past few years, at least for the Russian GLONASS system. As China's BeiDou and Galileo become operational, those will presumably be incorporated too. However, I'd guess that most of the improvement in user experience comes from the higher reliability than higher accuracy. Even if the errors from all systems were completely uncorrelated (which they are not), averaging the location reported by four systems gives you at most a factor of 2 in improved accuracy. On the other hand, if your chance of being able to lock onto enough satellites (within a given number of seconds) for one system is 80%, the chance that you can lock on to at least one of the four systems becomes 99.8%.
nickysielicki 10y ago
Anyone around here know details on the encryption used by Galileo, Beidou, and GPS? Google does not turn up much. It would be interesting to hear about how they're doing this. With the constraints that they have (receivers not necessarily always online to receive key updates, extremely low bandwidth to work with, systems depend heavily on this information, fast locks are important) it would not surprise me if the encryption scheme has big holes in it. On the other hand, some of these constraints can be dealt with by making receivers fall back to the unencrypted signal until they're locked long enough to get their new keys. And given that this is military, they might err on the side of security rather than accessibility. So who knows.
Waterluvian 10y ago
To me that's surprisingly inaccurate. With a corrected system, no ground reference data, we can get 10cm RMS, no?
- scblock 10y ago
  With appropriate ground corrections 5 cm is pretty easy with the current US satellites. Sub-meter in real time is also fairly easy with the help of WAAS broadcasts and good receivers. But if consumer hardware (like a typical $200 Garmin receiver) could reliably have sub-meter accuracy that would be a big improvement. But I'm no expert on the actual math of GPS.

With functioning clocks, Galileo is accurate to within a metre, according to this article. That's crazy - I had no idea it was that accurate.

by jblok 10y ago

With functioning clocks, Galileo is accurate to within a metre, according to this article. That's crazy - I had no idea it was that accurate.

digi_owl 10y ago

Apparently they wanted to make it even more accurate, but got pushback from USA before they feared it would be used by hostile forces.

Klathmon 10y ago
What's the fear with more accuracy? From my (completely layman) perspective once you've got a meter or so of accuracy, you've got what you need for weapons. What's further accuracy get you that some nations are against everyone having?
- nathancahill 10y ago
  A similar thing happens with commercial imagery satellites. Companies are forced to downsample their high resolution govt-only images to 30cm for the general public.
  - deleted 10y ago
    [deleted]
  - blackaspen 10y ago
    My understanding is that it's not exactly "by force" but rather a condition of funding. The U.S. Government is probably Digital Globe's largest customer.
    - blackguardx 10y ago
      No, it is by force. It is similar to ITAR regulations. If you break that rule, your management team is probably going to jail. It would be akin to spying for a foreign power. Source: I used to do some consulting for a satellite imagery company.
  - maxerickson 10y ago
    That's slightly different though, better imagery makes it possible to resolve more features. With the improved positional accuracy it's a 2 meter circle vs a 1 meter circle. What tactics does a 1 meter circle enable that the 2 meter circle does not enable? Also, DigitalGlobe only has 30 cm capability: https://en.wikipedia.org/wiki/WorldView-4 https://en.wikipedia.org/wiki/WorldView-4 Who is downsampling (DigitalGlobe/GeoEye was downsampling earlier 40 cm imagery for Google, to 50cm)?
- michaelt 10y ago
  There's no fear about accuracy - the plan is that Galileo will charge for high precision services. Indeed, you can buy centimeter-precision GPS services right now for applications like surveying and precision farming [1] - those are small markets, of course; self-driving cars are the real prize. The objection from the US amounted to the fact an early Galileo design would have reduced their ability to degrade satellite navigation in war zones. Later the design was changed, so the US can jam Galileo - which avoids the US objection, but makes Galileo less useful as a backup. [1] http://www.trimble.com/Positioning-Services/Trimble-RTX.aspx http://www.trimble.com/Positioning-Services/Trimble-RTX.aspx
madez 10y ago
I'm very disappointed that the EU bowed to their demands. It is the second clear sign I know that Europe dances to the USA's pipe; the other one was the grounding of the bolivian presidents plane in 2013. I hope that Europe eventually stops giving in to demands by the USA. [0] https://en.wikipedia.org/wiki/Evo_Morales_grounding_incident https://en.wikipedia.org/wiki/Evo_Morales_grounding_incident
- trimbo 10y ago
  Or maybe the European team simply agreed with the concern?
  - madez 10y ago
    Now, that is a valid concern. So far the first I read. Maybe some countries in Europe also wanted to see Snowden catched.
    - dogma1138 10y ago
      You do understand that the security concerns of Europe and the US are mostly overlapping right?
      - madez 10y ago
        Exactly, mostly. I think Europe should have efficient and effective measures to ensure it's safety also when they don't align.
  - dmichulke 10y ago
    Would there be a reason why GPS with 10m accuracy is OK but Galileo with 1m is not?
    - nickpsecurity 10y ago
      GPS has better than 10m accuracy in another operating mode. Only the military is allowed to use that one, though. Then they don't want Galileo being 1m accurate? Probably same military reasons.
drzaiusapelord 10y ago
This is actually untrue. The US didn't like that the EU was using bands close to GPS so if there was a conflict where the Russians or Chinese were using Galileo to target American troops, the US would have no choice but to shoot down or otherwise disable Galileo satellites by force. No one wants this, so the EU chose a different frequency that could be jammed without jamming GPS. Accuracy was never a concern. Galileo can't do better than a meter for many reasons, not the least of which is number of satellites, clock accuracy, and cost. https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)#Tension_with_the_United_States https://en.wikipedia.org/wiki/Galileo_(satellite_navigation)...
- madez 10y ago
  Then Europe should treat shooting down of Galileo satellites as an act of war and react as such. It's not Europes business to make it easy for the USA to wage war.
  - drzaiusapelord 10y ago
    Europe is part of NATO and has major incentives to cooperate with the US. In the scenario where the US would have to shoot down Galileo sats, would most likely be one where the US is protecting Europe from China or Russia as we're talking WWIII. I imagine this little story is little more than a tempest in a teapot designed to enrage Euro nationalists. The reality is that when you're in a shared defense agreement, your weapons systems, including nav systems, need a high level of cooperation. A frequency shift isn't the tragedy you're making it out to be.
    - madez 10y ago
      In the scenario you mentioned Europe could turn off Galileo if deemed necessary, no need for the USA to shoot it down. The solution taken just makes it easier for USA to wage war against Europes interests.
      - drzaiusapelord 10y ago

athenot 10y ago

With India, China and Russia launching their own positionning systems, I wonder if it would be possible to interpolate an even higher precision by listening to all 5 signals at the same time. (I don't know enough about signal processing to know if that's a possibility or not.)

ekimekim 10y ago
(warning: armchair expert, I've just read a bunch of wikipedia pages) I believe there's still sources of systemic error that would affect all the signals similarly, such as atmospheric interference, so even taking (for example) the average of the reported position from all the services may not improve accuracy that much. https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_Positioning_System https://en.wikipedia.org/wiki/Error_analysis_for_the_Global_... is a good read.
- maxerickson 10y ago
  The typical approach seems to be to consider all the visible satellites together (rather than solving for the position indicated by each constellation and averaging them). So in practice having more satellites means that a good position measurement is possible more of the time.
- kittenmittens 10y ago
  You can also reduce some of the atmospheric interference by modeling it using both the L1 and L2 signal.
jessriedel 10y ago
Not only is it possible, it's already done in many (most?) smartphones made over the past few years, at least for the Russian GLONASS system. As China's BeiDou and Galileo become operational, those will presumably be incorporated too. However, I'd guess that most of the improvement in user experience comes from the higher reliability than higher accuracy. Even if the errors from all systems were completely uncorrelated (which they are not), averaging the location reported by four systems gives you at most a factor of 2 in improved accuracy. On the other hand, if your chance of being able to lock onto enough satellites (within a given number of seconds) for one system is 80%, the chance that you can lock on to at least one of the four systems becomes 99.8%.

nickysielicki 10y ago

Anyone around here know details on the encryption used by Galileo, Beidou, and GPS? Google does not turn up much. It would be interesting to hear about how they're doing this. With the constraints that they have (receivers not necessarily always online to receive key updates, extremely low bandwidth to work with, systems depend heavily on this information, fast locks are important) it would not surprise me if the encryption scheme has big holes in it. On the other hand, some of these constraints can be dealt with by making receivers fall back to the unencrypted signal until they're locked long enough to get their new keys. And given that this is military, they might err on the side of security rather than accessibility. So who knows.

Waterluvian 10y ago

To me that's surprisingly inaccurate. With a corrected system, no ground reference data, we can get 10cm RMS, no?

scblock 10y ago
With appropriate ground corrections 5 cm is pretty easy with the current US satellites. Sub-meter in real time is also fairly easy with the help of WAAS broadcasts and good receivers. But if consumer hardware (like a typical $200 Garmin receiver) could reliably have sub-meter accuracy that would be a big improvement. But I'm no expert on the actual math of GPS.