Why the distance from the drone to anchor is negative?

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yajuan2018
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Joined: Sat Aug 25, 2018 11:17 am

Why the distance from the drone to anchor is negative?

Post by yajuan2018 » Sat Aug 25, 2018 11:24 am

I used six anchors for the loco positioning system.I got some distances with negative values.I want to know why it is negative and whether the precision of the distance I measure for the anchors affects the coordinate values?

arnaud
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Joined: Tue Feb 06, 2007 12:36 pm

Re: Why the distance from the drone to anchor is negative?

Post by arnaud » Mon Aug 27, 2018 12:42 pm

The measurement we get from the UWB radios contains an "antenna delay" component: basically the radio signals takes some time to travel in the PCB traces and the antenna and when converting the time of flight to distance this account for about 150m. This antenna delay is compensated by the Crazyflie however this compensation has been measured at about 1m, bellow 1m the measurement becomes less linear and this can cause negative measurement if you are too close to the anchor.

In a practical system this is not a problem since negative measurements will be ignored and the other distance measurements will be >1m and so will be accurate enough to allow for a position estimate to be calculated.

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