I have two 3D surfaces that heavily overlap. For those of you familiar with airport imaginary surfaces these are imaginary surfaces for two runways that are near each other so the imaginary surfaces for each overlap. I need to merge them together keeping only the lowest surfaces of the two into the new surface. From there I plan on generating isolines of the new surface that can be used on a 2D map. I cannot figure out how to merge these two surfaces together in this way. Attached video are the surfaces together.