5 ms·

Is this similar to how the US used to mandate that civilian use of GPS was off by a certain amount?

dmoy 3y ago
Yes, it's ostensibly still for defense purposes in China
Apes 3y ago
A bit different. The GPS restriction was to prevent GPS on a device moving over 400 mph (I think that's roughly the speed?), and to limit accuracy to within a few meters rather than a few centimeters. The restrictions were intended to prevent the use of civilian GPS systems in precision missiles. Not a lot of civilian uses require anywhere near that speed or accuracy. It's a lot harder to justify grossly inaccurate geographic data as not hurting civilian uses.
- deleted 3y ago
  [deleted]
- fragmede 3y ago
  you're referring to the CoCom Limits on GPS receives, which limits functionality when the device is moving faster than 1,900 km/h aka 1,200 mph) and/or at an altitude higher than 18,000 m (59,000 ft), so you can't build a home made ICBM with it. Technically it's supposed to be and and not or, and high altitude amateur aerial ballonists tend to hit that flight ceiling, and so have a list of chipsets they can use in their balloons that don't stop working when they get too high. https://en.m.wikipedia.org/wiki/Coordinating_Committee_for_Multilateral_Export_Controls https://en.m.wikipedia.org/wiki/Coordinating_Committee_for_M...
  - klabb3 3y ago
    I never understood how this works, at least effectively. Isn’t this just a device DRM? If you can build an ICBM you can probably hack a gps receiver, or build an unlocked one, no? If that encryption key is in every gps device, surely it must be available on eg darknet. And thus you could use existing gps infrastructure (ie avoid the expensive part of launching your own satellites). What am I missing?
    - userbinator 3y ago
      There's no encryption, it's just a limit in the firmware. What am I missing? The collective intelligence --- or lack thereof --- of the bureaucracies that come up with these laws.
throwway120385 3y ago
It wasn't a pre-set error, rather each satellite was originally configured to broadcast a low-precision coarse signal and a high-precision signal and the high-precision signal could only be decoded using an encryption key. They later released the encryption key when civilian applications took off.
- froh 3y ago
  iirc there still are several signals broadcast, a rare public high precision signal (for land surveyors), a high precision stream (military) and a high enough precision stream (public navigation)
connicpu 3y ago
Sort of. It uses a pre-defined transformation that doesn't interfere with street navigation. If you're on a street it will precisely reflect that value as well as any other GPS. But it makes it difficult to perform purely GPS-based instrument navigation, which in theory makes it harder to conduct eg missile strikes.
rsaxvc 3y ago
No, the US one is basically error(like noise) injection and has been disabled: https://www.gps.gov/systems/gps/modernization/sa/ https://www.gps.gov/systems/gps/modernization/sa/ The Chinese one is effectively a warped coordinate system, see GCJ02: https://en.m.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China https://en.m.wikipedia.org/wiki/Restrictions_on_geographic_d...

dmoy 3y ago

Yes, it's ostensibly still for defense purposes in China

Apes 3y ago

A bit different. The GPS restriction was to prevent GPS on a device moving over 400 mph (I think that's roughly the speed?), and to limit accuracy to within a few meters rather than a few centimeters. The restrictions were intended to prevent the use of civilian GPS systems in precision missiles. Not a lot of civilian uses require anywhere near that speed or accuracy. It's a lot harder to justify grossly inaccurate geographic data as not hurting civilian uses.

deleted 3y ago
[deleted]
fragmede 3y ago
you're referring to the CoCom Limits on GPS receives, which limits functionality when the device is moving faster than 1,900 km/h aka 1,200 mph) and/or at an altitude higher than 18,000 m (59,000 ft), so you can't build a home made ICBM with it. Technically it's supposed to be and and not or, and high altitude amateur aerial ballonists tend to hit that flight ceiling, and so have a list of chipsets they can use in their balloons that don't stop working when they get too high. https://en.m.wikipedia.org/wiki/Coordinating_Committee_for_Multilateral_Export_Controls https://en.m.wikipedia.org/wiki/Coordinating_Committee_for_M...
- klabb3 3y ago
  I never understood how this works, at least effectively. Isn’t this just a device DRM? If you can build an ICBM you can probably hack a gps receiver, or build an unlocked one, no? If that encryption key is in every gps device, surely it must be available on eg darknet. And thus you could use existing gps infrastructure (ie avoid the expensive part of launching your own satellites). What am I missing?
  - userbinator 3y ago
    There's no encryption, it's just a limit in the firmware. What am I missing? The collective intelligence --- or lack thereof --- of the bureaucracies that come up with these laws.

throwway120385 3y ago

It wasn't a pre-set error, rather each satellite was originally configured to broadcast a low-precision coarse signal and a high-precision signal and the high-precision signal could only be decoded using an encryption key. They later released the encryption key when civilian applications took off.

froh 3y ago
iirc there still are several signals broadcast, a rare public high precision signal (for land surveyors), a high precision stream (military) and a high enough precision stream (public navigation)

connicpu 3y ago

Sort of. It uses a pre-defined transformation that doesn't interfere with street navigation. If you're on a street it will precisely reflect that value as well as any other GPS. But it makes it difficult to perform purely GPS-based instrument navigation, which in theory makes it harder to conduct eg missile strikes.

rsaxvc 3y ago

No, the US one is basically error(like noise) injection and has been disabled: https://www.gps.gov/systems/gps/modernization/sa/ https://www.gps.gov/systems/gps/modernization/sa/ The Chinese one is effectively a warped coordinate system, see GCJ02: https://en.m.wikipedia.org/wiki/Restrictions_on_geographic_data_in_China https://en.m.wikipedia.org/wiki/Restrictions_on_geographic_d...