When working on surfaces in Civil 3D, creating a boundary to limit the area used it straightforward. Of the choices we are given, Outer, Hide, and Show have been easy for customers and students alike to understand. However, overlooking the benefit and use of Data Clip seems to miss the mark when it comes to working with large surfaces. Let’s look at the process of assigning a Data Clip boundary type to a large surface instead of using Outer.
For this surface shown, I have a project area that covers the surface data that I will need. Nothing outside of it will be used so keeping it in the drawing only puts more strain on my system resources. From the many concerns users have about slow performance, it is a very common issue. This is where the Data Clip shines.
Before clipping the surface to the boundary, the Statistics page for the surface shows that it has almost 179,000 surface points.
After adding the boundary as a data clip, visually, the surface doesn’t even change so what gives? Let’s go back into the surface properties and look at the Definition tab. This is where the real magic happens (also required for the data clip to work if you added the data first). Move the entry for ‘Add Boundary’ to the first position in the list then rebuild the surface.
Now, not only does the boundary visually take effect with the surface limits, the statistics verify that only the data within the boundary exists in the drawing!
The boundary can still be stretched to include more area but at least now, you have reduced the amount of data that must be calculated every time an operation occurs that involves surface data. Next time you need to bring in large sets of surface data, you may find it helpful to add the Data Clip boundary before bringing in the data. This way, it may reduce the amount of initial processing time. Also, the file size benefits from this usage. The BAK file shows the entire surface file, pre-boundary. The DWG file is the file after the boundary has been applied.
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