  Versions of the following problem appear in several topics such as Gamma
Knife radiosurgery, studying objects with the X-ray transform, the 3SUM
problem, and the $k$-linear degeneracy testing. Suppose there are $n$ points on
a plane whose specific locations are unknown. We are given all the lines that
go through the points with a given slope. We show that the minimum number of
slopes needed, in general, to find all the point locations is $n+1$ and we
provide an algorithm to do so.
