Early on in my career using Civil 3D I quickly found that I had the need to find the intersection between a design surface and an existing surface when a simple grade to surface criteria is not feasible. In one project, I needed to abut my design surface (which was complex site grading of a gypsum stack for a phosphate mining client) to an existing mountain slope, essentially designing an expansion to make the mountain larger in a sense.
Finding this intersection between two surfaces is simple to do, but unless you have needed this task in the past it may not be as straight forward as you would think. In this post, I would like to explain one method that may help Civil 3D users who also need to find surface intersections.
As with any other task involved in finding relationships between two surfaces, we will start with a TIN Volume surface using the two surfaces that we need to find the intersection between. Once a TIN Volume surface has been created, we also need to make sure we have a surface style that displays User contours. After setting this TIN Volume surface to a style that shows user contours, we can then do an analysis to display user contours. Understanding that TIN Volume surfaces use elevation 0 as a common elevation between the two surfaces means that we can set our user contours to 0.
From here we can extract user contours from the TIN Volume surface. At this point our extracted user contours are set to elevation 0 (our user contour value), which gives us the horizontal layout of the surface intersections.
We now need to find the vertical layout of our extracted line, and to do so we simply drape it onto one of the surfaces we based our TIN Volume surface on, either will do since after all we are looking for the common location between both surfaces.
After draping our extracted line on either surface, we how have both horizontal and vertical layout of two surface intersections.
Finding surface interests is a simple task that arises from time-to-time, but may be a bit difficult to know where to start for newer users of Civil 3D or for any user who has never had a prior need.
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