by David Lewis
Boundaries are typically created from closed 2D polylines to limit a surface triangulation internally or externally. A boundary can contain lines and arcs. As the surface has been generated based on triangulation, Civil3D uses mid-ordinates to calculate where triangles interact with the boundary. Users also have the option to use destructive or non-destructive breaklines.
Boundaries are added to a surface by navigating to the surface definition in Toolspace prospector tab, right clicking boundaries and selecting ‘Add.’
There are 4 types of boundaries; Outer, Hide, Show and Data clip.
- Outer: Hides or excludes data outside its edge.
- Hide: Hides an internal portion of a surface such as water bodies and building footprints.
- Show: Displays a portion of a boundary within a Hide boundary such as an island in a pond.
- Data Clip: Acts as a data filter.
Note: An outer boundary should be amongst the final items added to a surface.
The mid-ordinate distance is the distance between the midpoint of a chord and the arc. The smaller the mid-ordinate the closer the triangulation surface is to the original arc.
Boundaries with Destructive and Non-destructive breakline
Users can control the relationship between the boundary and the surface by determining whether the boundary should be applied as either a destructive or non-destructive breakline.
- Non-destructive breaklines: Extends triangles exactly to the boundary line and preserve the original surface levels at their intersection with the boundary.
- Destructive breaklines: Removes triangles that extend beyond the boundary. This is typically used when the boundary does not represent a hard edge.