The Effects of Operation Order on Surfaces

The order in which Autodesk Civil 3D processes points can impact the resulting TIN surface. In addition, the order in which data is added to a surface, or subsequently ordered on the Definition tab of the Surface Properties dialog box, can impact the resulting surface.

Order of Data in a Data Definition Operation

When you add point data to a TIN surface, the result can be affected by the order in which Autodesk Civil 3D processes the points. You cannot control the order in which Autodesk Civil 3D processes points in a single operation; Autodesk Civil 3D adds points to the surface in an order that minimizes the time to perform the operation. The following are two ways the processing order can affect the resulting TIN surface:

• The order can affect the outcome when four points are co-circular (the circle determined by any three of them passes through the fourth). In this situation there are two ways to make a Delaunay triangulation of the four points, and the two triangulations could make the surface contours noticeably different. You can use the Swap Edge command to correct any problems of this sort.
• A second way is when two or more points are close together (less than .0001 units apart). Autodesk Civil 3D treats two such points as the same point, and whichever one gets processed second does not get added to the TIN. If the two points have different elevations, the order will therefore affect the resulting surface; in such a situation Autodesk Civil 3D will post a message to the Event Viewer. You can use the Modify Point command to assign the correct elevation to the point.

Effect of the Order of the Operation List

The order in which surface operations are performed can impact the resulting surface. Because of the incremental way a surface is built or rebuilt (the operations are performed one at a time in the order that they appear in the operation list) the order of the operation list is very important. You determine the order by the sequence of the commands you use to define the surface data. You can later modify the order in the Surface Properties dialog box. The following is a suggested order:

1. Add breakline and contour data.
2. Add point data.
3. Add any necessary boundaries, outermost first.
4. Perform any necessary edit operations.