A 3-dimensional data preparing method, comprising a first step of continuously taking digital images when moving from a first known point, via a second known point, to a third unknown point, a second step of generating tracking points from an image acquired at the first point, and sequentially specifying the tracking points on the continuously acquired images, a third step of obtaining 3-dimensional data of the tracking points based on the first and second points, a fourth step of sequentially obtaining a position of the third point, based on the orientation and the position data of the tracking point, a fifth step of obtaining position data of an image based on the first and second points, and a sixth step of sequentially obtaining position data of images from the orientation of the images at the second and third points and from the position data at those points.