Whats the Point with Survey Control?

O.K., before I get started I just want to make sure everyone knows that I come from a Civil/Survey background and deeply respect the profession. In fact, I recommend control be provided by a licensed surveyor prior to any renovation or new building project. However, after working with numerous trades and contractors in the construction realm Ive gained a new perspective on the role survey control plays when using 3d imaging during a renovation project. The unfortunate truth is that its not usually being placed far enough in advance to be utilized during the design phase for those renovation projects, if at all.

I guess I should lead with a quote from a foreman that really paints the first part of the picture. I was working with a mechanical contractor to help them integrate robotic total stations into their workflow. They had a very seasoned foreman on site for a high-rise project. I had just arrived and began to make introductions. They knew me as the surveyor that was coming out to help and the first thing out of his mouth was this: You know what I hate about surveyors? I was almost struck silent, not expecting that at all! He continued: As soon as you get two of them together nobodys right. The sad thing is that theres some truth to this. During the years I spent in that capacity it wasnt uncommon for there to be a sense of jubilation when busting someone elses work, a general disapproval for other firms was also fairly common.

The foremans comment that As soon as you get two of them together nobodys right has proven to be a reality thats repeated on projects that Ive been involved in. I tend to believe that its not because one person is more competent than the other, but because there are multiple factors to consider when evaluating the existing building (existing placement of structural entities, residual scribes and marks in the slab, etc.). Different opinions of those factors result in a variance between these control networks because the contributing evidence is given different weight.

Theres a real challenge for surveyors when establishing control in an existing building and Ive noticed a common habit of attempting to relay the existing site coordinates to the interior of the structure. This works great for the surveyors, but its worthless for the trades and designers because they need to relate their work to the actual conditions, not an accurate representation of where the gridline offset should be if it were built per plan in the first place. Ive seen this firsthand and by the time the trades began to install prefabricated pipe racks, they realized that there was a notable difference between the existing conditions and control lines. Measurements in the field between the physical condition and the established control could vary in the realm of inches when compared to the plans.

The next issue that seems to repeat itself is that 90% of the consumers Ive worked with prefer to have the deliverable close to the 0, 0 for X and Y as well as rotated to a parallel position to either axis (when there is not an existing model to align to). This doesnt support the large coordinate systems that come with State Plane or the odd angles that buildings sit at in reference to true north due to their alignment with the bearing of adjacent roadways.

Wed see a lot more success if we took the time to find out whats important to the end users instead of forcing our opinions on them. A short conversation with the contractor and trades will quickly reveal elements that require higher weight when re-establishing the control system. Communication with the designers will help you understand why they need the project oriented in a certain way to help them be more efficient with their workflow.

Ultimately, an understanding of the other contributing members on a project will allow the surveyor to better meet their demands. They dont need to disregard the standards that they hold, just implement a practice of providing a transformation for each structure on the site and integrating some verbiage better defining what was given higher weight during the control establishment and why.

About the Author

Ted Mort

Ted Mort: Operations Manager of Precision 3D Scanning, incorporates his diverse background in geomatics, computer science and construction to propel 3d imaging into the forefront of applied measurement in AEC. Mr. Mort has worked with renowned clients to successfully integrate advanced technology into their work flows.
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