Im trying to create a combined, existing grade surface in order to model a design layer on top and get corresponding cut/fill and mass haul maps. I have a LIDAR file from a year ago, as well as a survey that covers any changes in the area over the past year due to mining. My questions is; how to I combine these two surfaces, in a way that ensures the survey (surface shown in white on the image) takes precedence over the LIDAR (surface shown in red) wherever it may be present? I still need the LIDAR on the rest of the project, where the survey does not cover (shouldn't have changed in the past year). When I attempt to simply combine the surfaces into a compound surface, the elevation at each point is just wherever is highest between the two.