this post was submitted on 06 Mar 2025
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FCC chair says we’re too dependent on GPS and wants to explore ‘alternatives’. (www.fcc.gov)
submitted 2 weeks ago by Tea@programming.dev to c/technology@lemmy.world
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[–] SaltySalamander@fedia.io 9 points 2 weeks ago (1 children)

GPS literally triangulates your position using 3 satellites. It's how it works.

[–] Saik0Shinigami@lemmy.saik0.com 4 points 2 weeks ago* (last edited 2 weeks ago) (2 children)

No, you need 4 minimum.

Two satellites intersection places you on a circle. (all points possible)

Three satellites intersection places you on two possible points.

The last satellite give you the exact location.

However, the 4th can be omitted if one of the 2 points is not in a sane location. (eg well below the crust). And it's trilateration not triangulation.

The reality is that your phone/device will use like a dozen satellites.

[–] Ulrich@feddit.org 2 points 2 weeks ago (1 children)

Uhhh nope, that's incorrect.

The way triangulation works is by essentially measuring distance.

So 1 satellite distance puts you anywhere in a radius (circle) of that satellite.

2 Satellites puts you at 1 of 2 locations where those radiuses intersect.

3 satellites gives you a single location.

That's why it's called triangulation. Tri = 3

[–] notfromhere@lemmy.ml 9 points 2 weeks ago (1 children)

Oh boy, where do I even start? This comment is wrong in multiple ways. Let's break it down:

  1. "The way triangulation works is by essentially measuring distance."

    • Nope. This describes trilateration, not triangulation.
    • Triangulation uses angles, while trilateration uses distances. GPS works via trilateration.

  2. "1 satellite distance puts you anywhere in a radius (circle) of that satellite."

    • Kind of, but missing a crucial detail:
      • A single satellite defines a sphere around itself (not just a circle—you exist in 3D space).

  3. "2 Satellites puts you at 1 of 2 locations where those radiuses intersect."

    • Wrong. Two satellite distance spheres intersect to form a circle, not just two points.

  4. "3 satellites gives you a single location."

    • Mostly right, but incomplete.
    • In theory, three satellites narrow it down to two possible points, but one is often out in space or somewhere unrealistic, so it can often be ruled out.
    • However, because your device lacks an atomic clock, it typically requires four satellites to synchronize time properly.

  5. "That's why it's called triangulation. Tri = 3"

    • Nope. GPS does NOT use triangulation.
    • The "tri" in triangulation comes from angles, not the number of satellites. GPS uses trilateration, which is based on measuring distances, not angles.

Final Verdict

This comment is a trainwreck of incorrect terms and flawed explanations. If they meant "trilateration," at least part of it would make sense, but calling it "triangulation" completely ruins their credibility.

So, in short? No, their comment is very incorrect. 🚨

[–] Ulrich@feddit.org 1 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

A single satellite defines a sphere around itself (not just a circle—you exist in 3D space).

You are not getting a 3 dimensional location. That's why GPS coordinates only exist on 2 planes. You don't know what you're talking about.

Final Verdict

You're not just wrong, you're wrong AND you're a dick about it.

[–] Saik0Shinigami@lemmy.saik0.com 6 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

You are not getting a 3 dimensional location. That’s why GPS coordinates only exist on 2 planes. You don’t know what you’re talking about.

Coordinates on a sphere is a 3 dimensional location. The earth isn't flat.

Edit: Please education yourself before you're so confident in your own bullshit answer. https://gisgeography.com/trilateration-triangulation-gps/ and https://www.gps.gov/multimedia/tutorials/trilateration/

Satellites broadcast a sphere, not a circle. And that sphere doesn't land on the earth as a perfect circle for relatively obvious reason... since the ground isn't perfect flat, nor is the earth perfectly spheroid.

[–] Ulrich@feddit.org 3 points 2 weeks ago (1 children)

The earth isn't flat.

So which coordinate accounts for elevation? Latitude or Longitude?

[–] Saik0Shinigami@lemmy.saik0.com 4 points 2 weeks ago (1 children)

Lat/Long is only valid if elevation is valid. You can't reference a lat/long that is miles into space... or beneath the crust of the earth.

[–] Ulrich@feddit.org 1 points 2 weeks ago (1 children)

It's like you're making my point for me.

[–] Saik0Shinigami@lemmy.saik0.com 2 points 2 weeks ago (1 children)

A watch... or other simple gps device doesn't know what the elevation is.

Only one of the 2 selected points in a 3 satellite setup will be valid. And your device would have no idea which one is valid without elevation knowledge or a 4th satellite. Some devices can figure it out with just 3 satellites. Many/most won't. But ultimately it's the same thing. You need 4 pieces of input. Either 3 satellites AND elevation. Or 4 satellites.

So no. I've not made a point "for" you. You're just ignorant or specifically being obtuse on something you clearly don't understand.

[–] Ulrich@feddit.org 1 points 2 weeks ago (1 children)

A watch... or other simple gps device doesn't know what the elevation is.

My point, exactly

[–] Saik0Shinigami@lemmy.saik0.com 2 points 2 weeks ago (1 children)

Which is why they'd need 4 satellites. Read the whole post. Read the given sources. Stop being stupid.

[–] Ulrich@feddit.org 1 points 2 weeks ago (1 children)

I did read the whole post. Stop being an asshole.

[–] Saik0Shinigami@lemmy.saik0.com 2 points 2 weeks ago (1 children)

Clearly you didn't... You keep asserting false statements that have already been disproven with sources.

But ultimately it’s the same thing. You need 4 pieces of input. Either 3 satellites AND elevation. Or 4 satellites.

If a watch doesn't "know" elevation (barometer or other sensor providing such information) as the fourth data point... Then it NEEDS 4 satellites to make the data points whole. Making your statements yet again wrong. I've covered the cases... but you keep pushing false statements like "gps is triangulation" (completely incorrect) or "GPS uses 3 satellites" which is also only correct in one very specific case... Where it's largely 4 or more, with reality being more like as many satellites as the device can read the pulses for. Often being a dozen or even more...

I am making accurate and complete statements. You are the one peddling misinformation.

Hell to prove the point... my time server grabs GPS as it's primary source. It grabs up to 12 satellites to sync time. It shows me my sync status for lat/long as well... At 3 satellites it CANNOT get a lock for location OR time. At 4 it gets a weak lock.

[–] Ulrich@feddit.org 1 points 2 weeks ago (1 children)

You keep asserting false statements that have already been disproven with sources.

I don't. You just aren't paying attention to what I'm saying. You keep arguing up a strawman.

[–] Saik0Shinigami@lemmy.saik0.com 2 points 2 weeks ago

You are not getting a 3 dimensional location. That’s why GPS coordinates only exist on 2 planes. You don’t know what you’re talking about.

Proven wrong, as it's a "2d" map that only exists on a 3d plane. It's a slice of space that represents the moving target of "ground level". The point that this is a problem to take it as just a "2d map" is that you can't take 3 point readings from on top of a 1000 ft cliff and 3 feet away at the bottom of a cliff and expect 3 point measurements to actually give you accurate measurements since it's just "2d" right? Elevation matters as it needs to be accounted for during the calculations.

So which coordinate accounts for elevation? Latitude or Longitude?

Where elevation = ground. As stated...

Then you assert.

It’s like you’re making my point for me.

Which was in response to a post stating that the watch would need a 4th satellite or "elevation" in order to get a valid GPS value.

And after I further clarified for you how it works... again... and that I was NOT making your point. I assumed you simply didn't understand the point I was actually making.

My point, exactly

No... It wasn't your point at all because you asserted that GPS is 3 point triangulation. When it's 4 point Trilateration which only has the option of 3 point when the fourth value of elevation is already known, which the vast majority of devices that use GPS don't know.

What have I straw-manned? Can you point to it? What part of GPS needs 4 nodes/data points is vague?

[–] SaltySalamander@fedia.io 2 points 2 weeks ago (1 children)

three sats determine your accurate position. the fourth is for clock correction only.

[–] Saik0Shinigami@lemmy.saik0.com 2 points 2 weeks ago (1 children)

No.

Satellites project a sphere, you need 4 in order to get to a singular point. I've outlined each step. Fourth isn't for clock correction only. And even outlined why sometimes 3 is okay, but that requires additional logic that many gps devices sometimes can't compute, and even outlined that the vast majority of devices will use way more than 4.

https://gisgeography.com/trilateration-triangulation-gps/
https://www.gps.gov/multimedia/tutorials/trilateration/