  We work with rational rank 1 valuations centered in regular local rings.
Given an algebraic function field $K$ of transcendence degree 3 over $k$, a
regular local ring $R$ with $QF(R)=K$ and a $k$-valuation $\nu$ of $K$, we
provide an algorithm for constructing a generating sequences for $\nu$ in $R$.
We then develop a method for determining a valuation $\nu$ on $k(x,y,z)$
through the sequence of defining values. Using the above results we construct
examples of valuations centered in $k[x,y,z]_{(x,y,z)}$ and investigate their
semigroups of values.
