Have you ever wanted to create a model with a accurate Toposurface but were unhappy with how Revit ‘cleans up’ the edges? Maybe you were trying to do a presentation graphic and wanted to isolate you site. The key is in combining the use of Section Boxes (or Crop Regions) and Building Pads.
(EDIT- See bottom for easier method)
Here is how my Toposurface looked. I purposefully made the Toposurface much larger then it should have been, so I would be able to use a Building Pad & Section Box combo to slice it back. The goal was to create a round outline for the site. There is a model line circle just visible in the image.
Next sketch the building pad outline. The trick here is that the outline of your Building Pad needs to be entirely inside of the Toposurface (hence the over modeling). I wanted a circle, so I created a doughnut that would give me a decent void area that I could then crop.
Next is the finished Building Pad. I gave it an extreme offset (-2000′) so I would have plenty of room for the Section Box to do it’s thing.
Finally, I turned on the Section Box (View Properties) and used top & side views to adjust the boundaries, which cropped away my doughnut hole Building Pad.
You’ll notice I have multiple Toposurfaces overlapping to get the River running through the area. This resulted in needing two Building Pads, one for each Toposurface.
EDIT- So thanks to a few tweets (@twiceroadsfool & @jadamthomas), it appears I completely overlooked a built in Revit feature that does exactly what I wanted, with ALOT fewer steps. Imagine my surprise when I discovered the button label ‘Split Surface’. The only benefit I see to the above route is it maintains the overall Toposurface, so you can go back and edit your boundary in the future.