It's a real method for analyzing blood splatters.
To find the area of convergence, investigators typically use string to
create straight lines through the long axis of individual drops,
following the angle of impact along a flat plane, for instance the
floor or wall where the drops are found. Following the lines to where
they intersect shows investigators where the victim was located when
the drops were created.
To find the area of origin, investigators use a similar method but
also include the height calculations. This creates a 3-D estimate of
the victim s location when the drops occurred. For example, if the
area of origin is determined to be only two feet above the area of
convergence on the floor, the analyst may presume the victim was
either lying or sitting on the floor. If it is five feet above the
convergence, the victim may have been standing. This analysis can be
done using strings and a protractor, mathematical calculations or
( Source: forensicsciencesimplified.org)
Refer Wikipedia for knowing more about string method.