Surveyors use 3D scanning to provide accurate as-builts for the renovation of an historic Denver landmark.

Scan of ornamental lion's head on building facade.
For nearly 100 years, the Denver Auditorium Theater has served as one of the city’s key performance venues, hosting events from rodeos and country western music concerts to performances of Shakespeare and the Colorado Ballet’s annual Nutcracker. Built in 1908, the auditorium’s design included a portable proscenium (the plane separating the stage proper from the audience and including the arch and the curtain within it), which allowed it to be used as a general purpose building for up to 12,000 people or a theater with the seating capacity of 3,326. It has been used exclusively as a theater since it was remodeled in 1955.

As the cornerstone of the prestigious Denver Performing Arts Complex, the auditorium is proposed for a $75 million renovation to provide a unique and acoustically superior venue for opera, ballet, theater and music performances. David Evans and Associates Inc. (DEA) of Portland, Ore., was hired to provide the project’s architect with as-built drawings of the original structural elements.

Shrinkwrap of 14th street face of the auditorium.
The quality of as-built drawings is critical to the architectural design and reconstruction of any historic structure. Without sufficient and accurate information, especially during construction, change orders can multiply—something nobody desires. However, capturing accurate as-built information of old structures is challenging and can be dangerous. Historic buildings are rarely square and the structural beams and roof trusses can be inconsistent. And, in fact, the building itself may not be sound.

On the Denver Auditorium project, one of the most important areas to map was the auditorium’s attic—a maze of cat walks, ductwork, piping, lighting, and finally, steel trusses and rafters that were the basis of the original 1908 roof structure. The architect needed as-builts—accurate as-builts—of the roof trusses in order to tie the existing roof into the new design and construction.

The roof trusses resembled the sides of old steel I-beam railroad trestles. To complicate matters, we assumed that all the trusses were uniform to each other when the project started because visually they appeared to be. But when we began measuring, we found that each truss was different—at a different angle or length. There was nothing typical about the structure—again emphasizing the importance of accurate as-builts.

While measuring, we never forgot that there were only fragile acoustical tiles between us and the theater chairs 70 feet below. If we used conventional methods, we would have had to wear safety harnesses and climb the rafters to locate the critical points. It would have been very dangerous. Instead, we chose to utilize our Cyrax 2500 3D laser scanner (Cyra by Leica Geosystems, Atlanta, Ga.) to complete this project. The scans captured real-time 3D data and furnished extensive detail in remote and otherwise inaccessible locations. We were able to scan the rafters and trusses with all the supports, as well as the pipes, ducts, beams and catwalks. Everything within the scanner’s field of view was collected as data for further mapping.

Without the scanner, it would have taken us two to three times as long and not yielded the detail captured with the scanner. As it was, our two-person crew was able to keep the scanner on the catwalks and place targets only on the trusses and beams. Using conventional equipment, we would have had to take accurate reflectorless shots on the 3⁄8 inch wide flanges of the trusses of the I-beams. This would have been time-consuming and unverifiable if we had ended up with any questionable shots.

Interior walls, constructed during the previous remodeling, covered the windows of the building. To ensure that the new floors would be constructed at the correct elevation, we provided the architect with the exact location of all of the windows to re-establish the proper elevation for the design of the new interior floors, which had been removed in a previous renovation.

To assist the architects in determining the proper floor elevations and other critical elements of the renovation, we scanned the outside of the auditorium to measure the building footprint, the windows and the attic to locate the roof trusses. From these scans, we were able to map these elements with complete dimensions.

The laser scans of the exterior of the building captured its magnificent fa?e of years past in great detail. Very intricate lion heads were one of the architectural elements captured on the fa?e, which could be modeled to within 1⁄4 in with the laser scan data collected. The architect had the foresight to see the value that the laser scanning data would provide for historical preservation work that may be necessary, or for locating other piping or ducts and utilities captured in the scans in the attic for possible modification. One advantage to using the laser technology on historic or fragile structures is in the ability to measure the area to be surveyed without disturbing it. There is no need to position points or otherwise disturb the structure.

Scan of the ornamental design of the top of the building fa¿e columns.

Conventional Control

We used conventional survey methods to establish the accurate horizontal and vertical control that is critical to this type of project. If the control is not exact, the scans cannot be accurately registered. The survey control was based on street monuments and the traverse ran through the building, up a stairwell and into the attic. The traverse then went through the attic along the catwalk and out a door leading onto the roof. From the roof, the control traverse was able to close the loop back into the street monuments. Once the horizontal traverse was completed, a differential level loop was run over the same control points. The level loop had to turn back down the stairwell to get back to the street. After the traverses were complete and adjusted, the control points were ready for the scanning technology.

Using the survey control points set on the previous traverse, we registered the inside of the building to the outside to provide a very accurate as-built of the structure. AutoCAD drawings of the building footprint, window and door locations, and the interior structural roof components were provided to the architect. We also provided “shrinkwraps” (visual renderings) of the laser scans, so the architect could see all the data that was captured for possible future use.

While not all of the data collected in the laser scans was required by the client—including the lion heads—we archived the complete set of data so if a question arises, it can be answered without revisiting the site.

Shrinkwrap of the attic above the stage.

Laser Scanning Leverage

Using Cyrax technology, the as-builts were completed safer, faster and in greater detail than if the structure had been shot conventionally. And, instead of hundreds of points captured conventionally, the Cyrax technology captured literally millions of points that can be transformed into two-dimensional plan drawings and/or three-dimensional models to provide the architect with nearly any view of the structure they need. The safety risk to surveyors was lessened because we did not have to crawl around the beams and trusses in the attic of the structure to position points. In all, work that would have taken three to four weeks to complete conventionally took a week and a half using DEA’s laser scanning methods, and the client has access to more accurate and complete information.

One advantage to using this technology on historic or fragile structures is the ability to obtain very detailed mapping of an area to be surveyed without physically touching the surface. We can map a delicate feature, like the Denver Theater’s lion heads—and not alter or harm it in any way. There is no need to position points or otherwise disturb the structure. We are also able to perform the work without interrupting the use of the facility by the public.

With the detailed and accurate as-builts produced with the scanning technology, we were able to provide our client with the information they needed—and much more—to enhance an auditorium that, with its history and splendor, will provide a venue for performing arts patrons for years to come.