GPRS and True Point Partner on a Case Study in Chicago

The client is converting a 1980s office building to a luxury hotel one block from the Magnificent Mile, and needed to locate tension cables and rebar to accurately place mechanicals. To facilitate the design, the client needed precise documentation of the substructure and surrounding structural elements.

When drilling holes in a post-tensioned slab, inaccuracies could produce costly and sometimes catastrophic results. Ground Penetrating Radar Systems Inc. (GPRS) uses ground penetrating radar to locate, identify and mark post-tensioned cables and rebar in multiple areas of concrete on several floors, but the process of manually documenting these physical markings in CAD can be tedious, and measuring and modeling such a complex system of cables by hand can produce inaccuracies.

With TruePoint Laser Scanning, GPRS’s markings can be captured, in addition to all the elements of the surrounding structure, and aligned to the design model quickly and accurately. The combination of the laser scan and ground penetrating radar provides an overlay of multiple datasets, giving the client a high-definition 3D comprehensive view of the entire structure, both visible and invisible.

The client was provided with indexed point clouds for each floor in .rcp and .rcs file formats (ready to be used in Autodesk products). In addition, the client received AutoCAD 2015 2D floor plan drawings (in .dwg and .pdf file formats). The CAD drawings were aligned to the design drawings and included linework of the GPR markings and the point cloud x-referenced in.

In addition to the main purpose of capturing GPRS’s markings, the laser scan provided as-built documentation to verify existing conditions of the structure and all of the remaining Mechanical, Electrical and Plumbing, and Architectural features. The client was able to use the point cloud data to compare against the construction documents, minimizing their drawing or modeling hours, and preventing errors and omissions.

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