Variation in Co-ordinates of Tag

Wireless Connectivity Ultra-Wideband
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1

Hi everyone,

We have placed our Tag at a stationary position. In the logs which I have pasted below, it shows that the distance from the Anchor to Tag is almost exactly same (21.02 and 21.07), but there is variation in the coordinates (y-axis coordinates 1.50 and 2.42). Any reason for this?

I thought the coordinates are calculated based on the distance.

12B9[53.35,4.67,0.00]=3.38 578F[33.43,4.77,0.00]=19.19 0837[0.38,0.26,0.00]=51.89 0F24[73.30,5.14,0.00]=21.07 le_us=5310 est[52.44,1.50,-0.21,92]
12B9[53.35,4.67,0.00]=3.32 578F[33.43,4.77,0.00]=19.26 0837[0.38,0.26,0.00]=51.84 0F24[73.30,5.14,0.00]=21.02 le_us=7171 est[52.37,2.42,1.92,93]

Any idea about this would be helpful.

Thanks,
Varn

2

You also have a large variation in the z axis position.
You got 4 ranges which didn’t quite match up and so the system is trying to find a position that minimizes the errors. Sometimes it doesn’t take much of a range change to cause the position to move a fairly large amount in this situation.

Looking at your anchor locations 3 of them are on the +y side of the tag with only one at a lower y value and that one is a long way away and so will have relatively lower impact on the position. They are also all at the same height.
In other words the anchor geometry is poor, your position accuracy isn’t going to be good. Try varying the heights a little and if possible move one of the closer tags to be on the other side of the tag in the y axis.

1 Like
4

Thanks Andy

So suppose we have the anchors at almost the same height, and we put z-axis values as zero, will it affect the x and y axis (not z axis) accuracy on the Tag ? and also will it affect the distance calculation too?

5

The range measurements are 3d distance between tag and anchor, if you have an error in height then that’s going to give an error in distance.
So yes putting 0 in will impact the accuracy. But if they are all roughly at the same height then the errors won’t be enough to matter unless you’re right on top of the anchor.

e.g. if you’re 10 meters away and the anchor height is wrong by 5 cm then the range will be wrong by 0.1 mm, no where near enough to matter.
But if the anchor height is wrong by 50 cm and you’re only a 5 m away then that will be a range error of 2.5 cm, enough to start having an impact.

But even if the anchor positions are close enough having some variation in the heights is good.
If you are putting 4 tags in a room it’s fairly intuitive that if you put them in the corners you’ll get better results than if you put them all along one wall. Why would it be any different with height? If they are all at the same height the system won’t work as well as it would if they have some variety.