3D Checks
After 2D Checks passes cleanly, 3D Checks extracts real elevation data from your road surface and applies it to the lot geometry. These elevations become the starting point for the grading engine.
Prerequisites
- 2D Checks is complete with zero remaining issues
- A Civil 3D surface representing your road elevations is present in the drawing
Complete the 2D Checks step and submit the results before running this command.
Run the command
Type 3DLINEWORK in the Civil 3D command line, or click the 3D Checks button in the Core Tools panel of the DRTWRK Tools ribbon.
What the tool does
The 3D process builds on the validated 2D linework and adds elevation calculation:
- Collect objects and surfaces — selects linework from configured layers and collects Civil 3D surfaces assigned in the Layer Review modal
- Process geometry — performs the same splitting and cleaning as the 2D step
- Build node adjacency graph — reconstructs the connectivity graph
- Create permanent feature lines — generates feature lines in a specified Civil 3D site. Unlike the 2D step, these are not deleted after processing
- Extend open endpoints — identifies unconnected endpoints and extends them to the nearest projection surface, deriving elevation from that surface
- Add PI points and calculate elevations — inserts points of intersection along each feature line and projects them onto surfaces to assign accurate elevations
- Identify 3D-specific errors — flags feature line errors, extension errors, and elevation errors
- Export 3D data to JSON — serializes the 3D geometry for the grading engine
In the Layer Review modal, verify that the correct Civil 3D surface is assigned as the projection surface for each layer type. Incorrect surface assignments produce wrong elevations on your feature lines, which affects all downstream grading results.
The 3D wizard stages
The wizard guides you through three configuration stages before processing runs:
| Stage | Name | Description |
|---|---|---|
| 1 | Site Configuration | Set the Civil 3D site and road surface |
| 2 | Selected Layers | Confirm layers carried over from 2D processing |
| 3 | Construction Boundary | Define the area where grading will occur |
If a construction boundary does not exist in your drawing yet, draw it in Civil 3D first, then return and select it here.
Error review
After processing, the Grading Prep Review panel opens with the same workflow as the 2D step — Focus, AutoFix, Dismiss, Dismiss All, Reprocess, and Submit — plus additional categories for 3D-specific errors.
Common 3D issues:
| Issue | Cause | Fix |
|---|---|---|
| Missing surface data | Road surface not found or not selected | Go back to Stage 1 and confirm the road surface |
| Open endpoints couldn't extend to surface | Lot line endpoint falls outside the surface boundary | Extend the surface or move the endpoint inside the surface boundary |
| Pond boundary not closed | The pond top-of-bank line has a gap | Find and close the gap in Civil 3D |
| Property line not closed | The property line has a gap or isn't a single closed line | Fix it in Civil 3D |
Address or dismiss all errors before clicking Submit to proceed to Lot Grading.
Do not advance to grading until the 3D issues list is completely empty. Unresolved issues will cause problems during grading.
Arc handling
When feature lines with arc segments are added to a Civil 3D surface as breaklines, Civil 3D triangulates between the arc's endpoints by default, producing a chord instead of a curve. To improve surface accuracy along arcs, use a small mid-ordinate distance — a value of approximately 0.1 ft (≈ 30 mm) is recommended for curb returns and other tightly curved features.