Thanks to Dan Edleson for this third guest blog post discussing the imperfections that need to be recognized in the real world of Scan to BIM.
“If the world were perfect, it wouldn’t be.”
– Yogi Berra
The great thing about Revit is it makes it easy to be a perfectionist. When I sketch, I am often inclined to draw loose, rough lines. This is fine for conceptual work but doing documentation by hand has often frustrated me. I was never a fan of the T-Square in college and only used my Mayline once before I started producing all my projects in AutoCAD and tracing over them to get clean, straight lines on my hand drawings.
Revit takes AutoCAD’s perfect straight lines to the third dimension, which is great for a typical project, but can be problematic when the existing conditions you are modeling have several decades of warping that need to be documented. If you don’t have the funds to purchase an expensive plugin, you can still quickly and accurately document these imperfections in the built environment using some of Revit’s advanced modeling tools. Let’s look at how to model out of plumb walls, multi-sloped roofs, and warped floors.
The first thing I do is use flat floors to get everything modeled as accurately as possible. After I have completed the initial floors I go back and locate all the out of level occurrences. Then I create another floor type named Variable Thickness for topping off my flat floors anywhere that’s needed. In this floor type you will need to go into the structure of the floor and check Variable for one layer of the floor. Generally with scan data you don’t know what is inside the floor so there is only one layer. If you are trying to model the sandwich you will need to use your knowledge of the project to choose which layer is variable. Regarding thickness, I would suggest setting the default thickness of the floor to the minimum depth and aligning it accordingly in the model.
Once you have your variable floor type you will use a combination of a typical section with a very shallow clip plane (1’ or less) and a larger 3D section box to work from. Using the Modify Sub-Elements option for floors, you can change the surface based on what’s needed. The variable thickness comes into play as this happens, as the bottom will maintain it’s alignment. When you have completed this process use the Join tool and suddenly you have a clean floor that represents your existing conditions and still can easily be modified later. This process also works on flat roofs with crickets.
For pitched roofs you will want to model your roof with boundary lines and turn off all slopes. This will leave you with a flat roof initially but a lot more flexibility to modify and refine the roof and the slopes. With sloped roofs I keep Variable Thickness off because a typical functioning sloped roof shouldn’t have a variable thickness. Just like with the floors, use Modify Sub-Elements to make our roof as accurate as possible. Unlike with the floors, since Variable Thickness is turned off, we only focus on the slope of the roof.
I would suggest going in two passes over the whole roof. First model the roof as closely as you can using a 3D Scope Box with the PointCloud turned on. When you feel good about how it’s modeled, go in and use Sections with tight clip planes (1’ or smaller) to fine tune the slopes of your roof. No matter how good it looks in 3D, you should still use sections to fine tune it to match the point cloud. Complex roofs may require modeling several different portions individually, then using Join/Unjoin Roof to merge them.
For the complete article on Scan to BIM imperfections click here.
You can contact Dan at firstname.lastname@example.org
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