METHOD OF DRAWING OUT A CLOSED LINE

PURPOSE: A method for extracting a closed curve is provided to detect easily a closed curve by using characteristics and relationship of lines forming a closed curve. CONSTITUTION: An arbitrary line is selected and a set of lines satisfying a condition related the arbitrary line is obtained. Sum of sets T of lines is obtained. Each line is connected with both ends of a line k. Lines included in the sum of sets T are detected from the connected lines. The line k is removed from the sum of sets T if the lines included in the sum of sets T are not detected from the connected lines. The detecting process is completed if the lines included in the sum of sets T are detected from the connected lines. The number of elements in the sum of sets T is checked whether the number is more than 2. The lines forming the sum of sets T is decided as a closed curve if the number is more than 2.