3 ms·

sych a device would still require synchronization, it promises lower drift, but to eliminate drift you will always need to recallibrate to synchronize with refe

sych a device would still require synchronization, it promises lower drift, but to eliminate drift you will always need to recallibrate to synchronize with reference points (stars, beacons, GPS, ...)

sgt101 8y ago
I wonder what kind of improvement you can get by using several of the devices at once? Could some sort of consensus monitoring at least tell you what kind of margin of error you are working with ? I guess for some applications being 100m out is fine (for example an Astute in open ocean), but getting it that wrong in, for example, the Med or the Sound of Skye is probably a problem.
- planteen 8y ago
  Standard error decreases by the square root of the number of samples. So an order of magnitude improvement would need 100 sensors!
  - mattkrause 8y ago
    That’s true when averaging together iid samples, but you could probably do something smarter if you know about the likely errors and the sensors’ covariance. For example, if three of the four sensors agree, you should probably completely disregard the fourth, rather than averaging it in.
    - robotresearcher 8y ago
      > you could probably do something smarter Assuming measurements are independent and errors are Gaussian, the Kalman filter is this smarter thing. Variants exist for nonlinear systems. https://en.wikipedia.org/wiki/Kalman_filter https://en.wikipedia.org/wiki/Kalman_filter
  - justinjlynn 8y ago
    Of course, when you decrease the size of the sensor by half in each dimension while maintaining its error rate you've quadrupled the number of sensors. If you can increase the computing power similarly, or decrease the computing requirements for combining those sensor measurements - it quickly becomes feasible to use massive numbers of sensors to improve the standard error significantly - but it is a lot of ifs. Practical example, you'd only have to shrink the sensor by half 6 or 7 times to fit 100 in the same area as 1.
- i_am_proteus 8y ago
  Bear in mind that any ship operating near shore will be able to get visual or radar fixes from features on the coastline.

sych a device would still require synchronization, it promises lower drift, but to eliminate drift you will always need to recallibrate to synchronize with reference points (stars, beacons, GPS, ...)

sgt101 8y ago

I wonder what kind of improvement you can get by using several of the devices at once? Could some sort of consensus monitoring at least tell you what kind of margin of error you are working with ? I guess for some applications being 100m out is fine (for example an Astute in open ocean), but getting it that wrong in, for example, the Med or the Sound of Skye is probably a problem.

planteen 8y ago
Standard error decreases by the square root of the number of samples. So an order of magnitude improvement would need 100 sensors!
- mattkrause 8y ago
  That’s true when averaging together iid samples, but you could probably do something smarter if you know about the likely errors and the sensors’ covariance. For example, if three of the four sensors agree, you should probably completely disregard the fourth, rather than averaging it in.
  - robotresearcher 8y ago
    > you could probably do something smarter Assuming measurements are independent and errors are Gaussian, the Kalman filter is this smarter thing. Variants exist for nonlinear systems. https://en.wikipedia.org/wiki/Kalman_filter https://en.wikipedia.org/wiki/Kalman_filter
- justinjlynn 8y ago
  Of course, when you decrease the size of the sensor by half in each dimension while maintaining its error rate you've quadrupled the number of sensors. If you can increase the computing power similarly, or decrease the computing requirements for combining those sensor measurements - it quickly becomes feasible to use massive numbers of sensors to improve the standard error significantly - but it is a lot of ifs. Practical example, you'd only have to shrink the sensor by half 6 or 7 times to fit 100 in the same area as 1.
i_am_proteus 8y ago
Bear in mind that any ship operating near shore will be able to get visual or radar fixes from features on the coastline.