A method includes setting an exposure time of an image sensor included in a terminal device so that, in an image obtained by capturing a subject by the image sensor, a bright line corresponding to each of a plurality of exposure lines included in the image sensor appears according to a change in luminance of the subject. The method also includes obtaining a bright line image, including a plurality of bright lines, by capturing the subject, obtaining identification information of the subject, and obtaining an angle of light of the subject. The method further includes calculating a distance between the terminal device and the subject using the angle, obtaining a position of the subject that is specified by the identification information, and calculating a position of the terminal device using the distance and the position of the subject.