BIM Technical Standards: 3D Imaging
3D imaging, also known as laser scan or point clouds, is the process of recording existing conditions into 3D point data. This document assumes the reader is familiar with this form of data acquisition. Those unfamiliar with the technology should begin by reading section one of the GSA National BIM Guide Series 3.
Note: This document is a supplement to the requirements outlined within GSA National BIM Guide Series 3. Conformance to both this guide as well as GSA National BIM Guide Series 3 is a base requirement of the GSA BIM Guidelines for Revit.
The use of 3D imaging (scanning) to capture existing conditions must be a team based collaborative project. What, when, how a site is scanned must be agreed upon by the entire team prior to execution. This process is outlined in the 3D Laser Scanning Quality Management Program Guide, which is required.
File Structure and Organization
A clear and well organized data set will help insure success on the project. This structure should be planned out in advance of processing the 3D imaging data.
GSA requires that 3D imaging data be delivered using a particular organizational structure. It is suggested that this structure be used throughout the course of the project by the team. A template of the project folder structure is available for download.
GSA requires that all scan data be delivered in native authoring software (Faro, Leica, etc.) as well as in ASTM E57 format. It is the responsibility of the scan provider to convert all data to the ASTM E57 format.
Area map for Chicago Federal Center Plaza
Once scanning is complete, the team will meet to discuss the strategy for structuring the 3D imaging data. The output of this meeting will be the project's area map. The area map will drive the overall data structure as well as the naming convention for the 3D imaging data. Each area will become an individual data file to be referenced into the BIM authoring software.
Small projects may feature simpler area maps but still require them.
- The size of each area should be chosen based on achieving a workable file size for each area. Each area may vary in size based on the number of scans taken and the density of points captured.
- Where possible, existing area breakdowns should be used. Items such as the project's key plan should be considered as a basis for the area map.
- This may include sub-divisions of an existing area plan.
- No single area should generate a working point cloud file greater than 20GB in size.
- This size may be increased or decreased as part of the BEP development.
Data Origin Point (Coordinate Frame)
At a minimum, one set of registered point cloud data is to be in the same coordinate frame (origin point) as the BIM data on the project. This data should directly align to the BIM, when referenced to the origin point of the BIM, without manually moving the data within the BIM. Where possible, this should be handled via a UCS rather than a WCS. Scan World Coordinate System should be maintained in the city or state coordinate frames. See File Structure and Organization standard for additional information on BIM data origin points.
One set of data must share an origin point with the project's BIM data. In cases where the project has inconsistent origin points across it's BIMs, the largest of the BIMs is to be used to establish the origin point.
Chicago Federal Center
Revit model based on laser scan data of the Chicago Federal Center
Clear and concise naming is required to ensure future use of 3D imaging data. For data which has a default, manufacture naming will be rejected. The specifics of the naming convention are to be established as part of the BEP and must follow the standards outlined in the Naming Standard.
Maintaining Data Quality
GSA has adopted the GSA National laser scanning quality procedures, as outlined in the 3D Laser Scanning Quality Management Program Guide [DOCX - 4 MB] .
Note: Although this guide is geared toward Lidar based data, it is to be followed for all 3D imaging technologies used.
It is required that the creators of all 3D imaging project data will follow the QA/QC process outlined within the guide and that they will complete and deliver;
- Quality Management Program Checklists
- Laser Scanning Information Sheet
- Contractor - QA Project Plan Checklist
- Contractor - Data Acquisition Certification Report Checklist
- Contractor - Data Processing Certification Report Checklist
- Contractor – Field Quality Demonstration Report Checklist
- Contractor – Final Project Data Deliverable Report Checklist
For complete information on required 3D imaging quality requirements, see the Data Submittal standards.