Almost Triangulation : why you need at least two measures to guess where you
are ...

4 landmarks solution

3 landmarks solution

Why we should use the 3 landmarks solution

Why we should use the 4 landmarks solution

Always use landmarks as away as possible from you

Triangulation : A method of fixing an unknown point (for example in navigation)
by making it a vertex of a triangle whose other vertices and angles are known
(Collins Dictionary of Mathematics).