At this year's Royal Institution of Chartered Surveyors (RICS) BIM National Conference 2014, Christopher Gray, of the Mollenhauer Group, Los Angeles, gave an overview of his experience in creating a BIM model from laser scans and total station measurements for an existing structure, in this case a large mall in Los Angeles.
Mollenhauer was an early adopter of laser-scanning for what is known in the UK as “measured building survey”, which is unknown in the U.S. Mollenhauer started using Faro and Leica laser scanners together with total stations in measured building surveys. Initially Mollenhauer delivered 2D and 3D CAD drawings, but more recently they are delivering Revit BIM models. They are now able to “model existing buildings in BIM.”
For example, the Beverly Center in LA is an existing large mall of 2.5 million sq ft. Shopping patterns are changing in LA as a result of online shopping and other trends. The owners want to reengineer the entire space. They asked Mollenhauer to create a BIM model for the entire structure as a basis for the redesign.
Mollenhauer scanned the entire building with laser scanners and total stations.. 750 separate scans resulted in about a terabyte of point cloud data. They used Leica Trueview to visualize the scans and manually generated a Revit BIM model for the entire structure.
This is an iterative process. The client has to be involved at every step of the way. Christopher Gray emphasized that collaboration and communication are key – open and frequent dialogue with the client is essential. An agreed specification is essential and this has to include an agreed level of detail (LOD).
Required software includes tools for creating the BIM model from the point clouds. Christopher Gray said this is still very much a manual process and more an art than a science. Also necessary are visualization tools to allow the BIM and point clouds to be visualized and compared by Mollenhauer with the client.
Most BIM design tools including Revit are targeted at designing new buildings. Mollenhauer found it difficutl to use Revit for existing structures. Also BIM tools like straight lines. Mollenhauer found point clouds essential for curved details.
In this case the BIM model is the starting point for the redesign of the mall, but quoting architect Carl Elefante “The greenest building is the building that already exists.” Christopher Gray sees a future business opportunity in energy performance modeling for existing buildings the first step of which will be to create a BIM model.