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BIM Basics: Orthogonal Vs As-Built

As we continue to dive into the fundamentals of 3D BIM modeling, this post will discuss the differences between Orthogonal and As-Built BIM modeling. In our last post, we addressed the term Level of Accuracy and how that affects our modeling workflow. The Level of Accuracy certainly plays into the conversation when it comes to determining whether Orthogonal vs As-Built modeling is required.

When considering this question, understanding what the model is being used for is crucial.


The term Orthogonal simply means that the walls will be straight, and everything will be square. As we all know, no wall is completely straight. Settling and other natural occurrences happen over time and when documenting a building that is 20+ years old, this can be quite dramatic. For purposes such as demolition plans, arranging furniture, or basic architectural needs, modeling the structure orthogonally may be all that is needed.


If the project calls for using the model for fabrication, measurements, or the client simply wants the model to be true to the physical structures then an As-Built is necessary. The term “As-Built” refers to modeling the structure as it currently sits. When you hear As-Built, think as-is. Orthogonal could refer to how the structure was supposed to be built, however, As-Built is how the structure was actually built.

When modeling an As-Built, it is important to note the LOA the client needs. The LOA will determine how accurate the As-Built is. When modeling a structure Orthogonally, the LOA doesn’t play as much of a role. When modeling Orthogonally you’d make accuracy sacrifices to attain the straight lines and right angles.

Something important to consider is that the accuracy and ability to model truly “as-built” conditions depends upon the point cloud that is produced from scanning. If the point cloud doesn’t allow the modeler to clearly see the surface being modeled, then truly as-built conditions are impossible. In this way, LOA and modeling as-built conditions are integrally linked.

Another very common option is to use both methods throughout the same model. Oftentimes clients have a specific element that needs very precise modeling, and they don’t need the accuracy throughout the whole structure. It is important to have these conversations with the client before assuming that they want the entire structure modeled one way.


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