Civil3D geolocation file

Autodesk Civil3D can work with several built-in geographic coordinate systems. Using a DWG as a geolocation file for Revit models can be useful when:

• The Revit model can't be modified in any way
• Precise latitude and longitude values are unknown
• To improve map positioning accuracy when dealing with large, linear infrastructure models
• The geographic location and therefore the global coordinate system to be used are known
• The Revit Survey Point was established with local grid coordinates, northings / eastings, X / Y have been set

Workflow Requirements

This workflow will require:

• The use of Civil 3D
• Knowledge of the required coordinate system
• Optional: Revit, to check local coordinates and export a DWG for verification purposes
• Enabled feature flags and environment variables
  • allow-revit-reproject-skip
  • allow-revit-ignore-gcs

Please raise a service request to get both feature flags enabled. This will be a project-wide setting, affecting all new iModels. Connecting a Revit file without a geolocation file will still work as before.

Selecting a Geographic Coordinate System

Civil3D:

• Create a new DWG file
• Use command MAPCSASSIGN
• Select the appropriate geographic coordinate system (i.e.: UTM84-56S)

Image 1 - C3D Coordinate System menu

• Once a valid coordinate system has been selected, the Geolocation tab will become available

Image 2 - C3D Geolocation tab

• Turn on the background map and visually check that the correct area is visible
• Save the C3D file

Connecting model files

Regardless of the method of connecting model files, always ensure that:

• The DGN file is connected first and is selected as the file defining the geocoordinate system – ideally within its own connection
• The geolocation file is not modified, and it is used for each new iModel
• The geolocation file only needs to be synchronized once
• The GCS cannot be changed once connected. Updating the GCS will require a new iModel to be created first

Image 24 - Correctly positioned Revit model using a C3D geolocation file

Validating Results

Unless previously provided by a qualified surveyor, it can be difficult to select the correct GCS. In some cases, a standard UTM zone can be used. In the above example, UTM84-56S has been selected. Exporting a site drawing from Revit as a DWG and referencing this drawing to Civil3D can be useful to verify the GCS selected and correct placement.

Once attached to Civil3D and with the background map enabled, the reference should be located at the desired position.

Image 25 - Civil3D with referenced DWG

Notes