1. A 3-dimensional data preparing method, comprising a first step of continuously taking digital images of scenes in the surrounding when 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, a second step of generating tracking points from an image acquired at said first point, and sequentially specifying said tracking points by the pursuit of the points generated on the continuously acquired images, a third step of obtaining 3-dimensional data of said tracking points based on the result of orientation of said tracking points at said first point and at said second point and from position data of said first point and said second point, a fourth step of sequentially obtaining a position of said third point, i.e. an unknown point, based on the result of orientation of said tracking point acquired at said third point and based on 3-dimensional position data of said tracking point, a fifth step of obtaining 3-dimensional position data of an image including said tracking point from the result of orientation of the images including said tracking points at said first point and at said second point and from the position data at said first point and at said second point, and a sixth step of sequentially obtaining 3-dimensional position data of images including said tracking points from the result of orientation of the images including said tracking points at said second point and at said third point and from the position data at said second point and at said third point.