remove magnetometer and barometer, position ok?

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justinleeyang
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remove magnetometer and barometer, position ok?

Post by justinleeyang » Thu Feb 02, 2017 3:36 pm

hi,

If we remove the magnetometer and barometer, only with acc, gyro and LPS's distance data, we can get the crazyflie2's position ?
I see that the mag and baro is optional, the following code:

Code: Select all

#define SENSORS_ENABLE_PRESSURE_LPS25H
#define SENSORS_ENABLE_MAG_AK8963
if I remove the two lines code, maybe affect the position's result ?



arnaud
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Re: remove magnetometer and barometer, position ok?

Post by arnaud » Tue Feb 07, 2017 10:14 am

Hi Justin,

The pressure sensor and magnetometer are not used by default by the Kalman filter. The pressure sensor could help but is a bit noisy and the magnetometer is more questionable indoor (it will be affected a lot by external magnetic fields).

So the answer is YES, you get a position without magnetometer and pressure sensor, it is the position you have been getting with the Kalman filter in its default configuration.

/Arnaud

justinleeyang
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Re: remove magnetometer and barometer, position ok?

Post by justinleeyang » Wed Feb 08, 2017 2:10 am

hi, arnaud:

Got it, thanks!

In addition, default need 6 anchors, if I use 4 anchors, do crazyflie2 get the 3D position ? I know that the convex hull will be small, but I want to
get the position with as few anchors as possible, the minimum anchors is 4 ?

arnaud
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Re: remove magnetometer and barometer, position ok?

Post by arnaud » Wed Feb 08, 2017 9:51 am

For TWR (ToA) the minimum is 3, for TDoA the minimum is indeed 4, however in TDoA case you will get very bad positioning outside the convex hull. Depending on how you place your anchors you might be able to optimize the system to get good 2D estimates (a bit like gps: with overhead satelites/anchors we get good X/Y position and worse Z position).

justinleeyang
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Re: remove magnetometer and barometer, position ok?

Post by justinleeyang » Thu Feb 09, 2017 2:26 am

Got it, thanks!

justinleeyang
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Re: remove magnetometer and barometer, position ok?

Post by justinleeyang » Sun Feb 12, 2017 7:44 am

hi, arnaud:

another question, do you test the positioning accuracy with lps, acc and gyro throught EKF ?
maybe <=5cm ?

arnaud
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Re: remove magnetometer and barometer, position ok?

Post by arnaud » Mon Feb 13, 2017 10:44 am

Hi Justin,

I think some test has been done with a Kalman filter that indicates about +/-10cm accuracy in X/Y and a bit more in Z. Though I do not have the data available so I am not completely sure of it, but it a reachable ballpark. With some calibration and more anchor better accuracy might be reachable.

/Arnaud

justinleeyang
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Re: remove magnetometer and barometer, position ok?

Post by justinleeyang » Mon Feb 13, 2017 11:05 am

hi, arnaud:

about +/-10cm accuracy in X/Y and a bit more in Z, is the LPS's position method TWR or TDoA ?

arnaud
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Re: remove magnetometer and barometer, position ok?

Post by arnaud » Mon Feb 13, 2017 11:31 am

With TWR uising 6 anchors with no further calibration, there has been no formal measurement of TDoA yet.

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