What is this "gravity data" in the new object capture API?

I'm playing with macOS new Object Capture API. I'm pretty new to 3D and I can't find any information regarding this gravity data for 3D reconstruction used for object capture.

I used the CaptureSample app provided by Apple (link) and this is a sample of the gravity data 0.015480,-0.991253,-0.131063

And another question, how does the app calculate that data? What information does it use for that?

Thanks

What is this "gravity data" in the new object capture API?
 
 
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