Merging part of two surfaces representing landscape

Hi all,

I have two surfaces from photogrammetry converted to elevation points with geographical coordinates using AutoCAD Civil 3D. The file I upload to Rhinoceros is triangulated .dxf surface, using Drape tool I convert it into step file for further use in geotechnical software Plaxis (which suggests use of .stp surfaces).

Using one surface there are no problems at all, however, the photogrammetry data I need to compare are from two different years (1990 and 2015) - in 1990 there is just subsoil and in 2015 there is ~100 m landfill, which covers approximately 60% of the area of the whole surface. Now to the problem - in the area of the landfill, the surfaces are far away from each other and there is no problem, I can easily create soil volume between them. However, in the area where is no landfill, the elevation data are very close to each other, but not exactly the same, which causes insolvable problems in Plaxis while generating volumes from surfaces (due to large number of very small volumes, where two surfaces overlap). And it’s not possible to solve it manually, because I have 70k points and I need details to be preserved in the surface.

TL;DR: Is there a way how the two horizontal surfaces could be connected to one, if the elevation (z) difference is smaller than a prescribed value? Or manually selecting the area, where the two surfaces should connect and form one?

I hope I managed to explain my problem clearly.

Hi Honza - one thing that comes to mind is using the Patch command in Rhino and giving it a zone of overlapping points - it will find some middle-ground and interpolate the points. I guess you’ll need to experiment with number of spans (in Patch) how large an area, etc and no doubt there will be some clean-up and trimming to do but it might be a way out.