Vertical Variation via 3D Polyline
Vary corridor height using the Z elevation of a 3D polyline on a named CAD layer in a linked DWG — works with any CAD package that can export 3D polylines, not limited to Civil 3D.
How the 3D Polyline Method Works
The 3D Polyline form scans CAD layers from linked DWG files in the Revit project and reads the 3D length and vertex Z coordinates of polylines found on those layers. After you select the layer and the matching polyline length, AutoBRIDGE uses the Z values along the polyline to determine the target elevation at each corridor station, computes the delta, and writes it to the chosen parameter.
comboBox1) from the linked DWG — AutoBRIDGE populates comboBox2 with the 3D lengths of all polylines found on that layer. Then pick the polyline length matching your corridor. This two-step approach lets you identify the correct polyline when multiple exist on the same layer.
Prepare & Link the DWG File
Create a 3D Polyline in the DWG
In your CAD application, draw a 3D polyline along the road profile. Each vertex must have a distinct Z value matching the design elevation at that position:
- AutoCAD: Use the
3DPOLYcommand. RegularPLINEpolylines are 2D and cannot store varying Z values. - MicroStation / BricsCAD: Use the equivalent 3D polyline tool ensuring Z is set per vertex.
- Place the polyline on a clearly named layer (e.g.
AL-PROF-FRL) — this is what AutoBRIDGE uses to identify it.
Link the DWG into Revit
Go to Insert → Link CAD in Revit. Select your DWG file and ensure the correct coordinate system is used:
- Use Auto - By Shared Coordinates if the DWG uses the same shared coordinate system as the Revit project.
- Use Auto - Origin to Internal Origin only if the DWG origin matches the Revit internal origin.
After linking, the DWG layers become available in the form's comboBox1 layer list.
Form Layout
The 3D Polyline form shares the same 5-zone structure as the Fixed Level and Model Line forms. The unique feature of Row 1 is that the 3D Polyline groupBox contains two cascading combos — Layer Name (65%) and PolyLine Lengths (35%) — matching the two-step source selection.
Select Family, Parameter, Layer & Polyline
Pick the Corridor Family & Parameter
Select the corridor from comboBox5 and the parameter from comboBox4. Both are available immediately — no dependency on the DWG layer selection.
Select the CAD Layer (comboBox1)
The 3D Polyline groupBox in Row B shows comboBox1 populated with all CAD layer names from linked DWG files. Select the layer that contains the 3D profile polyline.
After selecting the layer, comboBox2 populates with the 3D lengths (in metres) of all polylines found on that layer. Each entry is a rounded 3D chord length — use the value closest to your corridor total length.
Select the PolyLine Length & Set Direction
Pick the correct polyline length from comboBox2. The preview canvas updates to show the polyline Z profile as the blue segmented line. Set Parameter Direction (Up or Down) and verify the green band looks correct before running.
Verify Preview & Run
The elevation preview blue line will follow the vertex Z values of the 3D polyline as a segmented polyline — not a smooth curve. The number of segments depends on how many vertices the polyline has in the DWG. More vertices give a more accurate representation of the road profile.
Click RUN. The pipeline reads the vertex Z values from the selected polyline, interpolates at each corridor station, computes deltas, writes parameter values, rebuilds loft forms, and reloads the family into the project.
Troubleshooting
| Symptom | Cause & fix |
|---|---|
comboBox1 (Layer Name) is empty | No linked DWG in the project, or DWG has no layers with polylines. Link a DWG using Insert → Link CAD. |
comboBox2 (PolyLine Lengths) is empty after layer selection | No polylines exist on the selected layer, or they are 2D polylines (no Z variation). Check the DWG and use 3DPOLY to redraw. |
| Blue preview line is flat | The polyline is a 2D polyline with a single uniform elevation. Redraw as a 3D polyline with per-vertex Z values. |
| Blue profile at wrong elevation vs red base Z | Coordinate system mismatch. Re-link DWG with correct shared coordinates. |
| Wrong polyline selected | Multiple polylines on same layer — compare the 3D length in comboBox2 to the known corridor length and select the matching one. |
| Geometry inverted after RUN | Wrong direction. Toggle Up/Down and re-run. |