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Adjusting the accuracy of a corridor model in Civil 3D involves refining how the software calculates and represents the corridor's geometry. This is primarily controlled by frequency settings, which determine how closely the corridor aligns with the alignment, profile, and cross-section details.

Here’s a step-by-step guide to adjust corridor accuracy:

1. Open the Corridor Properties
Select your corridor in the drawing.
Right-click and choose Corridor Properties from the context menu.
2. Go to the Frequency Tab
In the Corridor Properties dialog box, switch to the Parameters tab and locate the Frequency column for each baseline and region.
Alternatively, click the Set All Frequencies button to globally adjust the frequency settings.
3. Adjust Frequency Settings
The frequency settings control how often sections of the corridor are sampled along the alignment. You can adjust these for:

Tangents: The spacing of corridor sections along straight segments of the alignment.
Curves: The spacing of sections along curved segments.
Spirals: The spacing along spiral transition curves.
Profile Grade Points: Ensures sections are added at grade breaks in the profile.
Key Stations: Adds sections at specific stations of interest.
Steps:
Click on the Set All Frequencies button (or edit individually).
Enter smaller spacing values (e.g., reduce from 10m to 5m) to increase accuracy.
Confirm the settings and click OK.
4. Add Key Stations (Optional)
If certain areas require more precision:

Select the corridor and go to the Modify Corridor panel.
Click Add/Edit Corridor Regions or Set Key Stations.
Add key stations manually to increase accuracy at critical points like intersections or sharp curves.
5. Rebuild the Corridor
After adjusting the frequency settings, ensure the corridor reflects the changes by rebuilding it:
Right-click on the corridor and select Rebuild Corridor.
Alternatively, enable Automatic Rebuild in the corridor properties for real-time updates.
6. Check Corridor Surface Accuracy
If your corridor includes a surface, you may need to refine the surface triangulation:

Open the Corridor Surface Properties.
Adjust the Supplementing Factors and Minimize Flat Areas settings to improve surface accuracy.
Rebuild the corridor surface to apply changes.
7. Verify Results
Use the Section Editor to review the corridor cross-sections and confirm the increased accuracy.
Check the corridor surface in 3D view or use analysis tools to ensure it matches the design intent.
8. Balance Accuracy and Performance
Increasing accuracy by reducing frequency can make your model more detailed, but it may also impact performance for large corridors. Use smaller frequencies only where necessary (e.g., at sharp curves or intersections).