Polygon detection device, polygon detection method, and polygon detection program

A polygon detection method performed by a computer, the method comprising:

• acquiring a ratio among lengths of sides of a reference polygon included in an appearance of a predetermined object;
• acquiring a photographic image of the predetermined object;
• detecting line segments from the acquired photographic image;
• forming at least one candidate polygon based on the detected line segments;
• and
• identifying, from the at least one formed candidate polygon, a polygon corresponding to the reference polygon based on a score value, the score value being obtained by using a degree of similarity between a ratio among lengths of sides each of the at least one formed candidate polygon and the acquired ratio among the lengths of the sides of the reference polygon,
• wherein the method further comprises:
• separating at least some line segments into a first group and a second group, an angle between each line segment in the first group and a predetermined line segment among the at least some line segments being larger than a predetermined value, an angle between each line segment in the second group and the predetermined line segment being equal to or smaller than the predetermined value;
• selecting a first preset number of line segments from line segments included in the first group and selecting a second preset number of line segments from line segments included in the second group;
• forming the at least one candidate polygon based on the selected first preset number of line segments and the selected second preset number of line segments;
• obtaining a degree of overlap between each of the at least one formed candidate polygon and a polygon including all line segments used to form each of the at least one formed candidate polygon;
• giving a weight to the score value, for each of the at least one formed candidate polygon, to obtain a weighted score, wherein the weight increases as the degree of overlap becomes higher;
• and
• identifying the polygon corresponding to the reference polygon based on at least one weighted score.

A non-transitory computer readable medium storing thereon a polygon detection program configured to cause a computer to:

• acquire a ratio among lengths of sides of a reference polygon included in an appearance of a predetermined object;
• acquire a photographic image of the predetermined object;
• detect line segments from the acquired photographic image;
• form at least one candidate polygon based on the detected line segments;
• and
• identify, from the at least one formed candidate polygon, a polygon corresponding to the reference polygon based on a score value, the score value being obtained by using a degree of similarity between a ratio among lengths of sides of each of the at least one formed candidate polygon and the acquired ratio among the lengths of the sides of the reference polygon,
• wherein the polygon detection program further causes the computer to:
• separate at least some line segments into a first group and a second group, an angle between each line segment in the first group and a predetermined line segment among the at least some line segments being larger than a predetermined value, an angle between each line segment in the second group and the predetermined line segment being equal to or smaller than the predetermined value;
• select a first preset number of line segments from line segments included in the first group and select a second preset number of line segments from line segments included in the second group;
• form the at least one candidate polygon based on the selected first preset number of line segments and the selected second preset number of line segments;
• obtain a degree of overlap between each of the at least one formed candidate polygon and a polygon including all line segments used to form each of the at least one formed candidate polygon;
• give a weight to the score value, for each of the at least one formed candidate polygon, to obtain a weighted score, wherein the weight increases as the degree of overlap becomes higher;
• and
• identify the polygon corresponding to the reference polygon based on at least one weighted score.