Measurement of existing buildings for design and renovation purposes is a service that has traditionally been performed either in house by architectural firms or outsourced to firms specializing in this practice. Using a variety of different techniques these measurements are usually taken either the old fashioned way with a tape measure and pencil, utilizing a single shot laser to get one dimension at a time or in cases where extremely accurate data is required a surveying crew may be called in to locate dimensions utilizing a survey total station. This data is then compiled and either a two dimensional floor plan is created or more often a three dimensional model is produced in order to utilize the design advantages of BIM. The resulting accuracy is dependent on the methodology utilized. If your data is limited or the capture method is antiquated, you can expect your results to be as well. However, often more accurate results are not necessary and the resulting deliverable will suit the purpose.

In many cases, however, more accurate and complete results are necessary. If designing an addition to a structure knowing the general location of the wall as measured by a tape measure or a single shot laser meter may not be enough. What if the wall is not plum? What if the wall cantors from top to bottom? That piece of steel may very well show up on site and be too short. I often recall stories of fresh “green” hires to my father’s electrical contracting business being sent to get the “wire stretchers” as the wire was too short. As the new hires would frantically search for the tool in vain, the rest of the seasoned veterans would have a good laugh at their expense. But stop a renovation project just as it starts due to a beam that’s an inch short, and I assure you no one will be laughing.

And how about prefabrication? Are you comfortable enough with your existing conditions survey that you feel confident in the ability of contractors to prefabricate components off site in tight fit configurations?

These situations call for the high level of accuracy provided from 3D laser scanning. Where traditional methods usually involve one or two measurements at each wall, window or door opening, 3D laser scanning captures thousands of shots along each element. Try seeing if a wall is plum or cantors from one or two measurements. Are you sure that room is square? With laser scanning, you can virtually see the entire wall, end to end, top to bottom. The chances of recording an incorrect measurement are essentially eliminated due to the sheer volume of measurements obtained.

Laser scanning however does not in itself assure the highest levels of accuracy. Like any process, the ability of the operators and the firm conducting the scanning and processing must be capable of utilizing the equipment properly and knowing its limitations. Larger project generally require the expertise of a land surveying company that knows laser scanning limitations and how to properly and accurately tie scans together to assure the highest levels of accuracy. I was recently told of a project that involved documentation of a large structure that was comprised of multiple pods connected by hallways all emanating at obtuse angles. From one end of the structure to the other certain MEP elements were recorded as being 6” and greater removed from their actual locations. While the actual reason for this occurrence is unknown it most likely could have been prevented by having a land surveyor establish an accurate baseline and a closed traverse to register the individual scans together, greatly increasing the accuracy of the scan registration.

Regardless of raw data accuracy, not all software packages that utilize 3D BIM modeling make it easy to use real world data. Design software likes for walls to be true and plum, floors and ceilings to be level. Unfortunately this isn’t the real world. Many architects opt to not have existing conditions models represent the real world due to the difficulty in designing with real world conditions. Rather than utilize models that reflect these less than ideal conditions often architects prefer the models to be adjusted to show “corrected” conditions. But here again 3D laser scanning can save the day. Models can be created showing square, true and plum walls to the same level of accuracy obtained from a single shot laser or tape measure however once the model is created the laser scan point cloud can be imported into the model with the point cloud being used as a reference for critical dimensions. Now, when the true dimension of that steel beam need to absolutely accurate, the designer can access the model, turn on the underlying point cloud and take the accurate dimension directly off of the point cloud, eliminating that potential 1/2” error.

Utilizing point clouds in this manner allows the architect to have the ease of working with an ideal existing conditions BIM model while having the advantage to take the most accurate real world dimensions possible, all while sitting in his office. Yes, you can have your cake and eat it too.

LandTech Consultants, Inc. is a full service civil engineering and land surveying firm highly immersed in 3D technologies for the A/E/C industries. We provide full 3D laser scanning and modeling services for building documentation in multiple formats. Contact us today to discuss your project.