Much like layout, BIM has to have some sort of control – something to reference in order to orient yourself and your content.
Every BIM file, whether CAD-based or otherwise, has an origin point. The trick on any project involving multiple design parties and subcontractors, is agreeing on where to line up models.
From the contractor’s perspective, this is usually dictated initially by the design team. If the architect/engineer decides to use a program like Autodesk Revit in order to produce their contract drawings, where they start modeling is very important.
Once we get our hands on these models, we can either decide to use their original origin or abandon it in lieu of something more standard. Most of the time we will reorient the file far enough up and to the right so that we only handle positive values.
For example, by moving the model from its origin, 0,0,0, to something distant such as 3000,5000,0, we do not have to worry about negative values. We usually choose the most southwest grid intersection as a general rule.
Setting this origin up front before we start building ensures everyone modeling from there on will line up with the overall federated model.
Zack Creach is a senior engineer for Holder Construction in Atlanta.