  In an article, E. Grafarend and B. Schaffrin studied the geometry of
non-linear adjustment of the planar trisection problem using the Gauss Markov
model and the method of the least squares. This paper develops the same method
working on an example of the determination of a point by trilateration in the
three-dimensional geodetic option for determining the coordinates $(x, y, z)$
of an unknown point from measurements known distances to $n$ points.
