Over the next few months I will be posting some tutorials and workflows for taking civil engineering models such as drainage layouts and retaining walls from AutoCAD Civil 3D to Revit. The reasons for these workflows are to increase the Level of Detail and information that is held within the models. For example, the coordination and documentation of foundations with new drainage and existing underground services can be achieved very efficiently with the use of AutoCAD Civil 3D and Revit. This is even more relevant with the introduction of Autodesk Collections which will have Revit and AutoCAD Civil 3D available to all! See this link for a full list of products that are available in the Autodesk AEC Collection
In this first post I will concentrate on the fundamental task of getting a TIN (Triangular Irregular Networks) surface from AutoCAD Civil 3D to Revit as a 3D TOPO.
AutoCAD Civil 3D and Revit each use slightly different algorithms for the triangulation of surfaces. This could potentially allow errors to creep in if we simply rely on points and use these points to build surfaces in Revit and Civil 3D. In practice you should create the Revit Surface directly from the AutoCAD Civil 3D triangles. In the example below you can see a triangulation model from AutoCAD Civil 3D with the points shown in red and the levels shown in blue.
In the image below the Revit Triangulation algorithm is shown in red. The points are connected in a different order and can cause minor differences in levels.
To ensure that AutoCAD Civil 3D is showing triangles, select the Surface and then select ‘Edit Surface Style’ from the Right Click context menu. Select the Display tab, make sure that the View Direction is set to Model and ensure that Triangles are visible and all other component types are switched off.
To ensure correct coordination to Revit you should clearly mark a survey station that you would like to reference and also a project base point. An example may look similar to the image shown below.
Note that in the above example the Survey Point was unclipped and moved to the Station ‘ST1’. You could also leave the Survey Point at 0,0,0 which would be the OS False Origin. You should never unclip and move the Project Base Point as this can affect IFC datum and coordination with other models.
Coordinates can be given from either the Project base point or the Survey Point. You will also have to multiply the Easting and Northing by 1000 to take into account the scale difference between the Survey (in Meters) and the Revit Project (in Millimetres).
AutoCAD Civil 3D Export to AutoCAD
The TIN Surface in AutoCAD Civil 3D is a special object that cannot be used easily in Revit. The solution is to export the AutoCAD Civil 3D surface as an AutoCAD drawing. This will result in 3D Faces which can then be used to build the Revit Topography.
Click the Application Button, then Export and then Export Civil 3D Drawing.
The Export Dialog Box will automatically add a prefix to the drawing name to identify this as an AutoCAD drawing.
One the export has completed the TIN surface will be represented as AutoCAD 3D faces. Make a note of the Layer that the 3D faces are positioned as this will be needed when creating the Revit Surface.
Delete all other information and just retain the 3D faces and the datum’s as shown in the image below. The datum’s are very important for the coordination of the model within Revit. Scale the AutoCAD model from the Origin 0,0,0 and set the scale factor to 1000 (scale from Metres to millimetres).
Start a new project using your template in Revit. Make sure you switch to the site plan as the view range primary top and cut plane will be set to 10,000 to allow you to see the topograpgy.
In the Visibility Graphics/Overrides dialog box make sure that the Project Base Point and Survey Point are visible.
Next you link the AutoCAD drawing into Revit. Make sure that you set the import units to custom factor = 1 to ensure that there is no scale change. Also bring the AutoCAD file in Centre to Centre.
Once the AutoCAD file has been linked it is a good idea to set the Visual Style to Wireframe to allow you to see the Setting Out information through the 3D faces.
Unclip the Survey Point and move to the Survey Station of your choice (In this case STN1). Note that you will need to unclip the Survey Point, move to the location and then clip the Survey Point. I would then suggest pinning the AutoCAD drawing along with the Project and Survey Points.
Your Model is now coordinated!
To create the Topography, make sure that you first set the category to visible. Click the Massing and Site tab and select the Toposurface Tool.
Click the ‘Select Import Instance’ from the context menu and select the linked CAD file.
Do make sure that you now select the Layer where the 3D faces (triangulation) are positioned. You will now have a Revit Toposurface with Identical triangulation to your AutoCAD Civil 3D model.
Hope this helps,