The increased availability of LIDAR data and other forms of large point datasets have brought new challenges to many Civil 3D users as they attempt to build surfaces from datasets containing millions of points. One of the challenges is, unlike traditional surveys, the LIDAR data may encompass an area much larger than the project area you are creating a surface for. At first you might think that the answer to limiting the extents of the surface is simple; we have created Outer Boundaries for surfaces in Civil 3D since the program was introduced. The problem with the traditional Outer Boundary is the order which it must be used in the build process of the Surface. First, points and any other surface data are added, and then the Outer Boundary is added last. This means the surface is built first using all the surface data, and then trimmed to limit the surface to the area inside the Outer Boundary. This is not a problem with traditional survey data as you are working with a reasonable number of points. But with LIDAR data and other large datasets performance can be a real problem if you must use all the points in a very large dataset when you only need to build the surface in a small area.
The solution to this problem is to use a Data Clip boundary. The major difference here is that the Data Clip Boundary is added to the surface first, before the points and other surface data. It then clips out any data outside this boundary before it is added to the surface. This greatly improves performance for surfaces built from large datasets as Civil 3D only calculates the surface data in the area you need to build the surface rather than from the entire dataset.