A position data interpolation method, comprising: continuously taking digital images of scenes in the surrounding in a process of moving from a first point, which is a known point, via a second point, which is a known point, to a third point, which is an unknown point; generating tracking points from an image acquired at the first point, and sequentially specifying the tracking points through the pursuit of points generated on continuously acquired images; obtaining 3-dimensional position data of the tracking points based on a result of orientation of the tracking points at the first point and at the second point and based on position data of the first point and the second point; and sequentially obtaining a position of the third point based on a result of orientation of the tracking points acquired at the third point and based on 3-dimensional position data of the tracking points.