Civil 3D Fundamentals: Surface Boundary Options

I’m starting a new series of fundamental posts.  I think they will appear regularly on Mondays from now on, but today, you get it on Tuesday.

I am working with a fun group this week doing things like channels, lagoons, dams, spillways and more.  We were building our surface to get started this morning, and someone asked what the difference was between adding a boundary as “non-destructive breaklines” or not.


Here is the original TIN.  The heavy black line is a boundary I’d like to add.


Adding a boundary without non-destructive breaklines eliminates the entire triangle that would be interrupted by the boundary.  It “destroys” the triangles it crosses.


Adding a boundary with checking the box trims each triangle and adds a data point from the trimmed triangle to the surface at the boundary location for a “neater” edge.


 A closeup of the added points.


When to use each one?  I tend to use the first option more often since I draw rough boundaries with the goals of eliminating gross errors.  The group I am working with today tends to use nondestructive breaklines around their boundaries because they must return 3D surface areas that are “flush” with their boundaries.  Each tool has its place.  Experiement to find which one works best for you.

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