Tell me about the confidence key

[mrmay-dev]

Hi all,

Haystack reports have a key called conf. I’ve seen it go as high as 115. What is this number telling me? What’s the scale?

My best guesses are:

• it’s the dBm of the beacon’s signal. This would allow a very rough estimate of the distance between the tag and the iPhone.

• it’s the estimated distance, in feet, between the tag and the iPhone sending the report. Using this as a confidence radius produces reasonable results.

I think the first is most likely, but the second produces reasonable ranges.

What am I missing or don’t know?

Thanks in advance

[michellarcari]

I'm also curious to know what that piece of data means, but my best guess is that it's the estimate distance between the tag and the reporting device. Anyone?

[humpataa]

I get confidence values up to 220 ... my guess is the distance to the tag: the closer the higher the more accurate the gps values. I believe it is based on the strength of the signal (dBm) which can be used to measure the distance.

[mrx23dot]

If we could intercept what an original airtag returns back via API
and what's shown in original map as radius then we could reverse engineer it.

[humpataa]

Just read in the author's paper that it likely represents the accuracy in meters. If you open google maps and look at yourself it shows a blue circle – "confidence" being the diameter of it – if I understand it right.

[mrx23dot]

Paper doesn't give details on confidence.
But GPS comes from the finder phone not from the tag,
so maybe it's related to BLE RSSI e.g. -115dBm

would be easy to reverse engineer it, do 5 measurements via the network, meters vs confidence value,
something like 1m, 5m, 10m , 15m, 30m I don't think it goes further.