PURPOSE: To obtain the closed area extraction method capable of easily extracting one part of closed area without requiring a complicated designation by an operator.

CONSTITUTION: A vector with the closest distance (d) from a specified point CP is selcted as a trace starting vector Vf0a (or Vf0b). When the specified point is found in the progress direction of the trace starting vector, the vector is traced clockwise when the specified point is found in the left of the trace starting vector and counterclockwise when found in the right. Thus, the vector group forming the minimum closed loop surrounding the specified point is traced and selected, and the closed area surrounded by this closed loop is extracted.