This paper discusses two optical processing systems for the rapid extraction of contours from a pair of stereo transparencies. For a given x-parallax, these systems provide a display of all contours present at the elevation corresponding to the parallax setting.
M. Parker Givens,
"Contour Visualization Using Coherent Optical Systems", Proc. SPIE 0045, Coherent Optics in Mapping, (1 October 1974); doi: 10.1117/12.953972; https://doi.org/10.1117/12.953972