In the old days when contours were polylines, it was very easy to break them and then move them to a demolition layer so that we could turn off existing contours that no longer applied to the site on the grading plan. In AutoCAD Civil 3D, you cannot break contours apart because they are an internal component to the surface. It is possible to extract the contours to polylines, but then the polylines will not be dynamically linked to the surface if more data is added.
There is a way in AutoCAD Civil 3D to achieve the same effect by using surface masks. A surface mask can be added through the Prospector.
In the Surface category, locate the surface to be masked and expand its branch and you will see Masks. Right-click on Masks to create.
You will be prompted to “select object(s)”. With the pickbox, you can select any of the following objects to mask your surface with:
- Polylines
- Circles
- Ellipses
- Rectangles
- Faces
- Survey Figures
- Feature Lines
- Parcels
- Surfaces
So as long as your finished grade surface has an adequate boundary, you can use it as the mask. Select the surface then press the Enter key. The Create Mask dialog will open. Fill out the dialog accordingly. A mask type can be inside or outside, just like a surface boundary. Masks can alternatively be used as locations to apply rendering materials too.
Click OK. The finished grade surface is now masking over the existing contours.
We do not need to sacrifice aesthetics just because we are dealing with object-oriented technology. Surface masks are helpful aides in keeping our plans legible by omitting needless linework without compromising the integrity of the existing surface.
– Cyndy Davenport
