As you might guess, the game of 3D connect the dots is a bit more sophisticated than the 2D version. In addition, you need the result to be a 3D model rather than just lines. To accomplish this, Civil 3D uses a computer algorithm that connects the dots in the most efficient and accurate way possible. This algorithm is known as a
Triangular Irregular Network (TIN).
The TIN algorithm works by connecting one point to at least two of its neighbors using 3D lines. Because each point connects to two or more of its neighbors, the resulting model looks something like a spider web made up of triangles (the T in TIN). Because the spacing between points is typically nonuniform, the triangles come in many shapes and sizes, which is why it’s called irregular (the I in TIN). The network (the N in TIN) part comes from all of the points being connected by lines, and the points and lines being related to one another. The
Figure below shows a surfacewith its TIN lines visible.
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| A surface model displayed as TIN lines. Note the irregular triangular shapes that make up the surface model. |
There’s even more to it than the triangles, though. In fact, the triangles are just a handy visual representation of the algorithm at work and, by themselves, they really aren’t all that useful. What
is useful is that the algorithm can calculate the elevation of any point within the area covered by the TIN model. So, even if you pick a point in the open space inside a triangle, the elevation will be calculated. This is what makes the TIN model a true model. It can be sliced, turned on its side, have water poured on it, excavated, and filled in—all virtually, of course. The capability of using surface models for these types of calculations and simulations is what makes them so useful and puts them at the core of Civil 3D functionality.
