  The PK-3 Plus laboratory onboard the International Space Station is used to
form complex plasma with a liquidlike particle subsystem in metastable state
and to observe the propagation of crystallization fronts corresponding to the
surfaces of crystal domains. We propose the "axis" algorithm of solidlike
particles identification, which makes it possible to isolate different domains
and their surfaces as well. Determination of the three-dimensional front
velocity is based on its definition implying that there exists a small area of
the domain surface propagating along some line perpendicularly to it. The
velocity measured in this way is an important characteristic of the plasma
crystallization kinetics. It proves to be almost independent of time and the
direction of front propagation and amounts to ca. 60--80 micron per second.
