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I've often heard people talk about locating a mobile phone by triangulating the signal from two masts.
However, as I understand it, a mobile phone mast has no way of detecting the bearing of a phone, it can only be used to make an estimate of the distance to the phone by using signal strength.
So, whereas bearings from two masts would give two lines, with the phone at the point where they cross, signal strength would give two overlapping circles, with the phone at one of two possible points.
Taking into account variations in signal strength, these two points will more likely be two areas, so what's the name for the technique of locating a phone by this method ?
Trilateralising, I think?
Thanks for that, I'll be able to use that word next time I hear someone using the word triangulation incorrectly and I want to be pedantic.
It looks like you have your answer but wouldn't triangulation imply the use of three masts not two?
I always imagined it worked the same way as Trilateration is described in that link, I just didn't know there was a different name for it.
triangulation works with straight lines to give a triangle where you are, trilateration works more like a Venn diagram (and also potentially in 3d as it's really 'spheres').
wouldn't triangulation imply the use of three masts not two
The triangle is formed by three points. The two masts and the phone.
As long as you know the position of two points of a triangle, and the direction from those points to a third point, you can work out the position of that third point.
Thanks, wwaswas, you've reminded me of something else I've been wondering about for a while.
http://singletrackmag.com/forum/topic/why-cant-a-gps-work-out-altitude
Bilateralising, shirley?
Good point, Cheezo.
At its simplest, trilateration involves two known locations and two possible points for a third location.
Bilateration would be a semantically more accurate description.