4 ms·

I wonder: if you can just measure the gyroscope readings and velocity, then knowing a starting coordinate, could you just calculate the current coordinate? What

• dayjaby 3y ago
  Your position would drift insanely fast. In a drone, gyro readings and velocity are being used in the ekf2 filter to calculate your position. But a GPS position is required to prevent longtime drift. Obviously, in GPS deprived situations, you have to think about alternatives.
• gliptic 3y ago
  The unknown part is drift caused by measurement error, which will stack up very quickly.
• magicalhippo 3y ago
  That's called dead reckoning[1]. The Kalman filter[2], which pops up on this site rather frequently, is often used for updating the current state. The issue is that sensors are not perfect. Not just noise, but they might be slightly off in one direction more often compared to another for example. These errors accumulate, and so you can be quite off after not that long of a time. [1]: https://en.wikipedia.org/wiki/Dead_reckoning https://en.wikipedia.org/wiki/Dead_reckoning [2]: https://en.wikipedia.org/wiki/Kalman_filter https://en.wikipedia.org/wiki/Kalman_filter
  • gloosx 3y ago
    Thanks for all the answers guys, of course I missed the most interestins parts in my naive theorizing :)
    • magicalhippo 3y ago
      Stay curious! Almost always there's good reasons if a seemingly-obvious solution isn't much used. Sometimes it can be hard to understand why without a lot of in-depth knowledge, as it can depend on somewhat non-obvious aspects, typically in the practical realizations like in this case. With perfect sensors, dead reckoning would work like a charm. However I find that thinking about the problem, coming up with these what-if solutions and then figuring out why they don't work, can be quite fruitful. Often leading to new knowledge that might actually be relevant down the line, and if not it's a great exercise in problem solving.
• charcircuit 3y ago
  You can only measure acceleration using an accelerometer. A gyroscope is technically still useful here for removing the gravity vector from the data accelerometer is reporting. measured acceleration = true acceleration + accelerarion error velocity = (true acceleration)t + (accleration error)t + v_0 + v_0's error position = (true acceleration)t^2/2 + (acceleration error)t^2/2 + (v_0)t + (v_0's error)t + p_0 + p_0's error The error grows quadratically meaning that this equation can only be used for a brief amount of time.
  • nextaccountic 3y ago
    > You can only measure acceleration using an accelerometer. A gyroscope is technically still useful here for removing the gravity vector from the data accelerometer is reporting. You can combine accelerometer and gyroscope data to give you a (position, orientation) signal that is more precise than either, using a Kalman filter. (You can add other sensors in like magnetometer too) Unfortunately even with this technique there is still drift that over time accumulates without bounds (the error gets so larger you become completely lost). If you can navigate from known landmarks you can eliminate this drift however. Such landmarks include the stars (if you can see the night sky), buildings and topographic features like in this post, or GPS
• izacus 3y ago
  This approach is used very commonly - e.g. every airliner, submarine and military plane will have such a navigation system (augmented with GPS these days obviously). The issue is that the system naturally drifts, so over time it will accumulate error which has to be mitigated somehow (e.g. in military equipment with finding a known landmark and fixing on it). The so-called INS systems are quite the marvel of mechanical technology: https://en.wikipedia.org/wiki/Inertial_navigation_system https://en.wikipedia.org/wiki/Inertial_navigation_system
• fransje26 3y ago
  Yes, this is how navigation was done "in the past", without GPS, using inertial navigation systems. And pilots would recalibrate their position along the way or before arriving "on target" using known landmarks. The fancier systems could recalibrate using known star positions.
• meindnoch 3y ago
  I wonder: have you tried googling the answer for your question? When searching for "accelerometer navigation", the first result is https://en.wikipedia.org/wiki/Inertial_navigation_system https://en.wikipedia.org/wiki/Inertial_navigation_system Don't be lazy.
• fl7305 3y ago
  In an aircraft, your "velocity" is usually the airspeed. This is often a lot different from the true ground speed.
  • SonicScrub 3y ago
    If you're getting data from a GPS, then the velocity readings are ground speed, which is the data input you need for an inertial navigational system.
    • fl7305 3y ago
      The context here is the design of a navigation system that works without GPS. Once you have a functioning GPS, the INS is not needed at that point. The INS can run in standby mode and be continuously calibrated using the GPS positions. If GPS is lost, the INS is used as a backup. But at that point, you no longer have the GPS velocity. So the normal thing to do is to integrate the acceleration data from your accelerometer, which gives you the velocity (+noise, +drift).
• AndrewKemendo 3y ago
  That double integral will get you with the noise unfortunately