Loco positioning system performance in TDoA 2 mode

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Joined: Mon Apr 15, 2019 1:10 pm

Loco positioning system performance in TDoA 2 mode

Post by mbarcis » Mon Apr 15, 2019 1:28 pm


First of all, I am sorry if this questions seems similar to the ones already asked, but it's hard to compare the expected behavior with the observed one and I have not found any questions about exactly the same setup as ours.

We've been trying to get the loco positioning system working with multiple crazyflies. We have positioned six anchors in the following points:
0: {x: 0.0, y: 0.0, z: 0.0}
1: {x: 0.699999988079071, y: 2.64, z: 0.0}
2: {x: 3.430000066757202, y: 1.3799999952316284, z: 0.0}
3: {x: 3.3399999141693115, y: -0.05999999865889549, z: 2.819999933242798}
4: {x: -0.38999998569488525, y: 0.7099999785423279, z: 2.8299999237060547}
5: {x: 3.3399999141693115, y: 2.27, z: 2.819999933242798}

They are a bit close to each other, but we were trying to keep the 2m separation and reproduce the recommended setup as closely as possible.

In this gallery you can see the results:

The single drone video was recorded using the TWR mode. It's not perfect, but I'd say it's good enough to continue our work.
The two drone demonstration on the other hand was made using the TDoA 2 mode. You can see the performance is much worse.

Is that an expected result for such small room in TDoA mode and 6 anchors? What steps could we perform in order to improve it?

We have already tried to improve the calibration of the whole system -- we have used Optitrack available in the room to measure exact positions of nodes. Unfortunately in order to do that we needed to bring the anchors closer together and the result was actually worse.

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Joined: Tue Jun 30, 2015 7:47 am

Re: Loco positioning system performance in TDoA 2 mode

Post by kristoffer » Thu Apr 18, 2019 9:02 am


I think it looks a bit wobbly in TDoA, it can probably be better.

What is the performance like if you fly one drone in TDoA at the same position as you did with TWR?

When you fly two drones you are getting closer to the edges of the space and I would expect the positioning to degrade a bit compared to the center if the space, especially sin you only have 6 anchors.

It could also be interesting to try TDoA3 since the order of anchors (and thus the anchor pairs used for) is randomized.

I see that your bottom anchors have z=0.0, which means that the origin of your coordinate system is located about 15 cm above the floor. It is fine from a system point of view, just wanted to check if it is intentional.

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