For those of you who have both Civil 3D and Revit in your toolkit, here are a few options to help you get your surface from Civil 3D into Revit.

Surface viewed in Civil 3D.

Revit has tools to create it’s own surfaces – called Toposurfaces – from either drawing data or from a point file (text file of XYZ co-ordinates). In this post we are going to take a look at creating a Toposurface directly from the Civil 3D surface object. The first thing to understand about the way Revit creates it’s surfaces is that just like Civil 3D they are formed from a series of triangles. Unfortunately, unlike Civil 3D, there is no way of automatically controlling how the triangles are created (no adding of breaklines, no option to swap triangle edges, etc). So, how faithfully Revit reproduces your surface may depend a lot on how you take it across – and there is no single method that works great for all circumstances.

Setting up the Civil 3D drawing

Create a new drawing with ONLY your Civil 3D surface in it. If you import a Civil 3D drawing into Revit, and you have both Civil 3D objects and the polylines, text, points and other AutoCAD information you used to create your surface, Revit can get confused with the co-ordinates. I have found the best way round this is to use Data shortcuts in Civil 3D to recreate the surface in an empty drawing, with a co-ordinate reference point (such as a Survey station or other known point). Civil 3D point objects don’t show up in Revit, so if you use a Civil 3D point as your reference marker, explode it before saving the file.

Importing into Revit

Using the Import CAD tool in Revit, you can import your Civil 3D drawing.

The best results are obtained when setting the import units to metres  rather than “Auto detect” (make sure Civil 3D has the AutoCAD units set to Metres!) and positioning Manual - Centre . This positioning is important – you may be tempted to put it at the correct co-ordinates (Origin to Origin), but as you will probably have some large co-ordinate values, you certainly won’t want to use these in Revit.

Use the Revit Survey Point and Project Base Point to align the surface drawing to your project. Use the “move” tool in Revit to move the entire import instance based on the reference point you added to the Civil 3D drawing, snapping onto the Revit Survey Point.

Surface From Contours

One option is to set the display of the surface in Civil 3D to show contours. This is achieved by using or creating a suitable contour surface style with the intervals set appropriately. If you use this option, then you need the contours spaced close enough to model the details of the surface, but not too close that you end up with a huge surface in Revit.

Use the Toposurface tool , “Create from Import”, “Select Import Instance” in Revit to create the surface by picking the import instance.

Switch to a 3D view in Revit, and then change the visibility / graphics settings so that the Toposurface is visible.

When you finish the surface creation, you will see the contours from the imported drawing, together with the shaded Revit toposurface. Notice where the Civil 3D contours disappear below the Revit surface, showing the differences in the way the two surfaces have been triangulated.

Surface From Triangles

You can also try using a triangle display from Civil 3D. Since Revit does not honour every triangle formed in Civil 3D, there will be some discrepancies in the results. Set the surface style in the Civil 3D drawing to one that shows triangles in both plan and model views.

The image above shows the Revit triangle sides highlighted which don’t conform to the Civil 3D triangulation. However, if your Civil 3D surface has triangles which are evenly spaced the you should get a reasonable result.

Using Civil 3D, you can create strata surfaces from your borehole elevations – but if you simply take the elevations of your borehole data and create a surface from it, you probably won’t like the results…

In the example above, the profile shows the strata surface touches the ground surface – but that’s because there are not enough strata levels to accurately portray the relationship to the ground.

Instead of using the borehole elevations directly, you can use the depths of the strata and build a surface from that. Use Excel or notepad and create a .csv file that contains the Easting, Northing and depth of the surface, and import it into a point group. I used Overrides in the point group properties to set the Point Level to the user defined field “Depth”.

Build a surface from this data, and you will have something that looks like this:-

The heights on the Strata surface are not heights at all, of course, but the values represent the depth of the surface below ground. But now we can create a Volume Surface from the two surfaces, which will create a new surface showing the depth of the strata below the existing ground.

The resulting surfaces now look like this in profile…

Notice how the strata surface follows the ground line using the interpolated depths.

The strata surface is a Volume Surface, and so cannot be used as a target for grading operations in it’s present form.

However, you can export the surface as a LandXML file, and then re-import it as a normal TIN surface…

..just make sure you uncheck the section that refers to SurfVolumes in the Import LandXML dialog box.