In scientific visualization, a vortex core line is a line-like feature tracing the center of a vortex with in a velocity field.
Several methods exist to detect vortex core lines in a flow field. studied and compared nine methods for vortex detection, including five methods for the identification of vortex core lines. Although this list is incomplete, they considered it representative for the state of the art (as of 2004).
\nabla\boldsymbol{v}(\boldsymbol{x},t)
Another is the Lambda2 method, which is Galilean invariant and thus produces the same results when a uniform velocity field is added to the existing velocity field or when the field is translated.