
FOAM: The Importance of Time Synchronization - fagnerbrack
https://blog.foam.space/foam-the-importance-of-time-synchronization-3934755ccc4e
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_-richard
The margin of error on this system, running on mobile devices with
inconsistent and unpredictable OS and network latency/overhead must limit its
usefulness.

It's cool though, and nice to see another .space in the wild.

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tfha
It's also very easy to fake/attack. Sybils in this system would not be
difficult to spin up.

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hndamien
How? nodes validate each other in the mesh.

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sliken
Just browsed it real quick. They claim you can locate something in 3D with 4
sensors, but as configured they can't differentiate between any positive Z
distance and any negative Z distance.

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TrueDuality
You actually can even if all the sources / transmitters are on the same plane.
It's pretty easy to conceptualize as well.

With one measuring point and it's distance to a fixed target, you know that
the target lies somewhere on the surface of a sphere with a radius equal to
the distance.

With a second measuring point and it's distance to the same fixed target you
can overlap those two spheres. Two spheres that overlap do so as a circle. You
now know the target lies somewhere on the circumference of the circle.

With a third measuring point and it's distance, it's sphere will intersect the
circle at precisely two points. This is the minimum required for GPS as it can
usually discard one of the points using other knowledge (your receiver is not
in space).

With a fourth measuring location the ambiguity is removed and you're left with
a single location.

The orientation and location of the spheres don't matter as long as you know
the precise locations of the measuring points, all measurements are taken
while the target is fixed (which is why time synchronization matters here),
and all the spheres overlap (in the real world noise, and mulitpath
reflections make this quite difficult).

Source: I worked on wireless trilateration for several years for a commercial
project.

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amelius
This video clearly explains the root of the problem:

[https://www.youtube.com/watch?v=wteiuxyqtoM](https://www.youtube.com/watch?v=wteiuxyqtoM)

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arthurroingbaer
More on FOAM's use of Time Synchronization for dynamic proof of location here:
[https://github.com/f-o-a-m/public-research](https://github.com/f-o-
a-m/public-research)

Product white paper:
[https://foam.space/publicAssets/FOAM_Whitepaper.pdf](https://foam.space/publicAssets/FOAM_Whitepaper.pdf)

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exabrial
I learned a lot from this, including that the Eiffel tower was scheduled for
destruction. Nowadays, you can't legally take a picture of it!

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fanf2
You can take a picture of the tower but not its lights.
[http://c4sif.org/2010/12/copyright-and-the-eiffel-
tower/](http://c4sif.org/2010/12/copyright-and-the-eiffel-tower/)

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olfactory
This is very cool. I have been thinking a lot about ideas in this space for a
few years.

