Anchor count for TDoA v2/v3

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theseankelly
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Anchor count for TDoA v2/v3

Post by theseankelly » Sun Jun 24, 2018 1:02 am

Hi -- it's unclear to me from the docs on the wiki whether 8 anchors are strictly required for TDoA 2/3 to work, or whether they just work better with 8 anchors. I've only got six anchors - am I limited to TWR or should I expect TDoA 2/3 to work too?

Thanks!
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arnaud
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Re: Anchor count for TDoA v2/v3

Post by arnaud » Thu Jul 05, 2018 9:51 am

TDoA works best when the Crazyflie is within the convex hull, ie. within the space formed by the anchor. This is why 8 anchors is better: it is very easy to make a 'cube' convex hull. With 6 you can make two triangles, one on top and one on bottom, and you will have a decent convex hull. So in short, it will work with 6 anchors.

However it still works outside. You will just get more noise in the direction escaping the convex hull (I am not sure how to express this one :). For example if you are outside on the Y axis, you will still have quite good position in X and Z, but the Y axis will become more noisy the further away you go. If you have more sensor like the Z-ranger, is is possible to put the anchors mostly on the top and use the Z-ranger for height (as long as you are in range ...).

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