1. A method for constructing a 3D model of a scene, comprising: acquiring first images of a first scene having unknown characteristics by a first camera; acquiring corresponding second images of a second scene having known characteristics by a second camera, the first and second cameras having a fixed physical relationship to each other; analyzing only the second images to determine corresponding positions of the second camera while acquiring the first images; and assembling only the first images into a 3D model using the determined corresponding positions and the fixed physical relationship of the first and second camera.