Relative Feature Lines in Civil 3D allow you to create dynamic, elevation-aware feature lines that automatically adjust their elevations relative to an existing surface. This is especially useful for designing grading objects, such as retaining walls, curbs, and roads, as the feature lines will update automatically if the parent surface changes.
Steps to Use Relative Feature Lines to Model a Surface
1. Create a Base Surface
Ensure you have an existing surface (e.g., Existing Ground) in the drawing to which the feature line will be relative.
2. Create a Feature Line
Go to the Home tab Create Design panel Feature Line.
In the Create Feature Line dialog box:
Give the feature line a name.
Assign it to a specific site.
Specify a style (e.g., Basic or Grading).
Draw the feature line in the plan view, or select an existing polyline and convert it into a feature line.
3. Set the Feature Line to Relative
Access the Feature Line Properties:
Select the feature line.
Right-click and choose Elevation Editor or go to Properties.
Set Relative to a Surface:
In the Feature Line Properties dialog, navigate to the Surface column.
Set the feature line to be Relative to an existing surface by selecting the surface from the dropdown menu.
Specify Elevation Offsets:
Use the Elevation Editor to assign vertical offsets if needed (e.g., 0.5m above the surface).
These offsets apply to all points or specific vertices on the feature line.
4. Model a New Surface
Add the Feature Line to the Surface:
Open the Toolspace palette and go to the Prospector tab.
Expand the surface where you want to include the feature line.
Right-click Definition Add Breaklines.
Select the feature line and specify the parameters (e.g., Weeding Distance and Supplementing Factor).
Adjust Surface Settings:
The surface will update automatically as the relative feature line adjusts based on the parent surface.
Editing the Feature Line
Dynamic Adjustments:
If the parent surface changes (e.g., due to new survey data or modifications), the feature line updates its elevations automatically.
Modify Offsets:
Change the vertical offsets in the Elevation Editor for precise control.
Best Practices for Using Relative Feature Lines
Keep it Organized:
Use descriptive names and assign feature lines to appropriate layers for better management.
Combine with Grading Objects:
Use relative feature lines in conjunction with grading objects to create dynamic grading solutions.
Use Styles:
Assign styles to feature lines to differentiate between relative and static lines visually.
Avoid Conflicts:
Ensure the feature line does not create undesired triangulation when added to the surface.
Applications
Road Design: Model curbs and edges of pavements that adapt to the existing ground surface.
Retaining Walls: Create wall foundations or top lines relative to a base surface.
Drainage Design: Model swales or berms that follow the terrain dynamically.
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