6 ms·

Is there any cheap, open source alternative to GPS for navigation? I'm thinking of an electronic sextant (or star tracker) for rough position estimation, with a

Is there any cheap, open source alternative to GPS for navigation? I'm thinking of an electronic sextant (or star tracker) for rough position estimation, with a few km accuracy.

PaulHoule 6y ago
I'm somewhat annoyed at the accelerometer/gyroscopes that are available to the public, it is like they are all gimped to prevent you from building a weapons guidance system. For instance, the Wiimote doesn't have the dynamic range to handle the highest accelerations you can generate waving your arms, which makes it hard to use that kind of thing for athletic training.
- brandmeyer 6y ago
  > like they are all gimped to prevent you from building a weapons guidance system. You can buy RLGN off the shelf for a couple thousand bucks. You can buy gyrocompass-capable MEMS off of digi-key for dozens of dollars (Murata). Its just market forces and cost. You don't need super stable IMUs for game controllers.
- michaelt 6y ago
  They're not 'gimped' by any sort of conspiracy. It's just extremely hard to make a pure INS navigation system. Even if you could measure your acceleration accurate to 0.00001 m/s/s, because it gets integrated twice to give position even that tiny error is going to give you a position that's out by 100m after an hour. And measuring acceleration precise to 0.00001 m/s/s is a demanding task - like weighing a car so precisely you could count the pages of a book on the back seat. That level of precision simply isn't available in the affordable MEMS market segment.
  - generalizations 6y ago
    > They're not 'gimped' by any sort of conspiracy. It bothers me when people go around labeling random stuff conspiracies like that's a legit dismissal. If they were 'gimped', they wouldn't be the only hardware. GPS is still gimped and will shut off over a certain height and speed specifically to prevent use in missiles. And the precision used to be regulated, not by expense, but to give the military the superior tool.
    - tialaramex 6y ago
      Specifically the position was originally deliberately noisy thus reducing its effective precision in the short term†. This was called "Selective Availability" and the US military were supposed to buy military receivers which handled a different channel on which noise was not introduced, thus giving them an advantage over an enemy lacking this feature - but this misunderstands economy of scale. So faced with a situation where your army is much more technically sophisticated and would benefit from GPS precision, but the GPS receivers everybody has in stock are for civilians and so suffer from the noise, the correct US decision was "Turn off Selective Availability" and it has been switched off ever since. Newer GPS birds lack this pointless feature entirely. †Because it's "just" noisy you can wait, and average out the noise. If you stand in one place patiently recording your apparent position, for long enough, the average is much more accurate. Or, one station which knows exactly where it is uses short range radio to tell moving stations what the error currently is in the signal, improving their accuracy. The latter is known as DGPS and still makes some sense without Selective Availability because the ionospheric conditions will be similar at a short range too, reducing error from those.
      - marsokod 6y ago
        The parent poster is not talking about that, he/she is talking about the COCOM limits placed on GPS receivers sold commercially: the GPS would not provide an output when traveling faster than 1900km/h at an altitude over 18km (though some manufacturers used a logical OR instead of an AND). This limits still applies and you need to get a special license if you want to get these limits removed (or you can buy Chinese).
        tialaramex 6y ago
        The parent poster wrote: >And the precision used to be regulated, not by expense, but to give the military the superior tool. Which was, as I said, referring to Selective Availability, and has nothing to do with the arbitrary limits which are still imposed on US made receivers.
    - michaelt 6y ago
  - PaulHoule 6y ago
    I've seen lists of "dual use" technologies which are export restricted, and INS is one of those.
  - jaywalk 6y ago
    > It's just extremely hard to make a pure INS navigation system. But if you go to the ATM machine and pull out enough cash after entering your PIN number, you can pay enough to make it happen.
- thereddaikon 6y ago
  They are definitely gimped to prevent you from using them in weapons. GPS receivers are the same way. Non Military units wont work outside of certain parameters.
- deleted 6y ago
  [deleted]

Is there any cheap, open source alternative to GPS for navigation? I'm thinking of an electronic sextant (or star tracker) for rough position estimation, with a few km accuracy.

PaulHoule 6y ago

I'm somewhat annoyed at the accelerometer/gyroscopes that are available to the public, it is like they are all gimped to prevent you from building a weapons guidance system. For instance, the Wiimote doesn't have the dynamic range to handle the highest accelerations you can generate waving your arms, which makes it hard to use that kind of thing for athletic training.

brandmeyer 6y ago
> like they are all gimped to prevent you from building a weapons guidance system. You can buy RLGN off the shelf for a couple thousand bucks. You can buy gyrocompass-capable MEMS off of digi-key for dozens of dollars (Murata). Its just market forces and cost. You don't need super stable IMUs for game controllers.
michaelt 6y ago
They're not 'gimped' by any sort of conspiracy. It's just extremely hard to make a pure INS navigation system. Even if you could measure your acceleration accurate to 0.00001 m/s/s, because it gets integrated twice to give position even that tiny error is going to give you a position that's out by 100m after an hour. And measuring acceleration precise to 0.00001 m/s/s is a demanding task - like weighing a car so precisely you could count the pages of a book on the back seat. That level of precision simply isn't available in the affordable MEMS market segment.
- generalizations 6y ago
  > They're not 'gimped' by any sort of conspiracy. It bothers me when people go around labeling random stuff conspiracies like that's a legit dismissal. If they were 'gimped', they wouldn't be the only hardware. GPS is still gimped and will shut off over a certain height and speed specifically to prevent use in missiles. And the precision used to be regulated, not by expense, but to give the military the superior tool.
  - tialaramex 6y ago
    Specifically the position was originally deliberately noisy thus reducing its effective precision in the short term†. This was called "Selective Availability" and the US military were supposed to buy military receivers which handled a different channel on which noise was not introduced, thus giving them an advantage over an enemy lacking this feature - but this misunderstands economy of scale. So faced with a situation where your army is much more technically sophisticated and would benefit from GPS precision, but the GPS receivers everybody has in stock are for civilians and so suffer from the noise, the correct US decision was "Turn off Selective Availability" and it has been switched off ever since. Newer GPS birds lack this pointless feature entirely. †Because it's "just" noisy you can wait, and average out the noise. If you stand in one place patiently recording your apparent position, for long enough, the average is much more accurate. Or, one station which knows exactly where it is uses short range radio to tell moving stations what the error currently is in the signal, improving their accuracy. The latter is known as DGPS and still makes some sense without Selective Availability because the ionospheric conditions will be similar at a short range too, reducing error from those.
    - marsokod 6y ago
      The parent poster is not talking about that, he/she is talking about the COCOM limits placed on GPS receivers sold commercially: the GPS would not provide an output when traveling faster than 1900km/h at an altitude over 18km (though some manufacturers used a logical OR instead of an AND). This limits still applies and you need to get a special license if you want to get these limits removed (or you can buy Chinese).
      - tialaramex 6y ago
        The parent poster wrote: >And the precision used to be regulated, not by expense, but to give the military the superior tool. Which was, as I said, referring to Selective Availability, and has nothing to do with the arbitrary limits which are still imposed on US made receivers.
  - michaelt 6y ago
- PaulHoule 6y ago
  I've seen lists of "dual use" technologies which are export restricted, and INS is one of those.
- jaywalk 6y ago
  > It's just extremely hard to make a pure INS navigation system. But if you go to the ATM machine and pull out enough cash after entering your PIN number, you can pay enough to make it happen.
thereddaikon 6y ago
They are definitely gimped to prevent you from using them in weapons. GPS receivers are the same way. Non Military units wont work outside of certain parameters.
deleted 6y ago
[deleted]