Patent ID: 8441440

Claim:
A position information detection device, comprising: an image capture portion which captures images, by projecting onto an image capture element light-receiving face via a camera lens, of discrimination marks which contains multiple geometric graphics, creates a virtual reference rectangle with vertices of specific points of the multiple geometric graphics and with two diagonals of which lengths are equal, and is arranged on the side of an indication target plane; a discrimination mark extraction portion which extracts geometric figures from images captured by said image capture portion at an attitude where lengths of two diagonals of a reference rectangle image projected by the image capture element light-receiving face are not equal; a reference rectangle extraction portion which extracts the reference rectangle image with vertices of specific points in said geometric figures; a focal length calculation portion which, based on a coordinate system specified by said reference rectangle image, calculates the focal length of the camera lens of said image capture portion with respect to said image capture element light-receiving face; and an indicated position calculation portion which, based on said coordinate system and said focal length, calculates an indicated position of said image capture portion with respect to said indication target plane.