Backsights (and lava caves)

[John Halleck]

On Wed, 22 Jan 2003, Sergey Sorokin wrote:

> [...]
 
> You must have at least three legs from each station to get all of them
> fixed. If you have a station with 2 legs than it can be located in two
> different places (unless it is directly on line between it neighbours),
> so you will need some extra data to fix it at the single location.

  Three legs from each station is ambigious, there are two solutions,
  mirror imaged across the plane defined by the three reference points.
  Although adding another constriant (not in the earth for satilite
  measurements, maybe away from the previous points for the cave)
  it can work.