Splines can be created using either the Model lines (Architecture > Model > Model lines) or Detail lines (Annotate > Detail > Detail Lines) command. For a long time, splines in Revit have been a major bugbear. The reason for this is that it is currently not possible to make a closed, periodic spline nor is it possible to trim the spline once created.
Furthermore, it is (still) not possible to snap to the start/end point so that the points are coincident. Note that if you try to move the start/end point directly, it will scale and modify the entire spline. To move only the start/end point, you need to use Tab to select it.
All of these limitations makes working with splines very difficult. In fact, there is actually not much you can do with splines within Revit. However, here are your options if you do want to work with splines:
Option 1: Native Revit splines
Since you cannot create a single closed spline within Revit you can either:
- Create a second spline or line and snap to the start and end point to fully close the spline. In this scenario, you’ll need to eye-in the tangency.
- Model an in-place mass which only has 2D line work in it. This method will allow you to snap to the end point although technically it is not ‘closed’. Again you’ll need to eye-in the tangency. You will also receive an error stating that there are two overlapping points. This can be ignored since if you try to delete the duplicate reference point it will delete the last segment.
- Create an adaptive component family, which is similar to the in-place mass method described above.
Option 2: Imported AutoCAD/Rhino linework
The workaround for this limitations is to use AutoCAD or Rhino. Create or modify the spline in AutoCAD or Rhino, and then re-import the geometry back into Revit. When importing, you’ll need to use ‘Import CAD’, not ‘Link CAD’. Once in Revit, you can then explode the Imported CAD spline. Revit will convert it into a Revit spline and split it into two parts. If a 3D spline is imported, it will be flattened to the current work plane once exploded within Revit. The method of course breaks the golden rule of not importing CAD geometry and especially not exploding CAD geometry. The CAD geometry therefore needs to be as ‘clean’ as possible and used sparingly.
Option 3: Dynamo
Using Dynamo to generate splines is probably the best workaround. Dynamo will allow you to create a closed, periodic NURBS curve, similar to what Rhino or AutoCAD can produce. (Although refer to this post to see some of the geometric differences when importing). In order to create Revit geometry, such as model lines or a floor, the closed spline will need to be split into two segments. Although we are left with two lines, they will be tangential unless modified manually. The final output of this workflow is similar to option 2 where we imported CAD linework however the benefit Dynamo has over this method is that you won’t need to keep deleting and reimporting the geometry. Re-running the Dynamo script will automatically update the Revit elements should the spline geometry change.