A system, comprising: a stereoscopic camera configured to acquire multiple pairs of images of a surface; a display; and a processor configured to: sequentially acquire multiple image pairs of a surface from the camera; incrementally construct a 3D model from the image pairs concurrently with the sequential image acquisition, by: for each currently acquired image pair, registering the currently acquired image pair to a location on the 3D model, and adding the currently acquired image pair to the 3D model when: a) the registration succeeds and b) a delta of the registered image pair exceeds a threshold; rendering the incremental construction of the 3D model on the display; and concurrently tracking the incremental construction by displaying a graphic indicator that simultaneously indicates: i) the registered location, ii) when the viewing distance is within a focal range, and iii) when the viewing distance is not within a focal range.