A Picture Perfect TrifectaLaser Scanning, Orthophotos and BIM

A 678Kb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE

From silent movies to vaudeville productions, the Saenger Theater has provided residents and visitors of New Orleans many hours of incomparable entertainment for over 80 years. First opened in 1927 and listed in the National Register of Historic Places, the theater has gone through a number of renovations and reformations in the last 80 plus years. In 2004, the Saenger Theater re Partnership, Ltd.* sought to restore the theater to its original state. Their vision was to return the theater back to the original 4,000seat capacity, revert to the original color scheme, repair nostalgic architectural details and incorporate 1920s doors, lights and windows.

Then Hurricane Katrina struck and the three-story, 70,000-sq.-ft. structure suffered severe damage as flood waters rose above stage level, filling the basement and orchestra seating area, damaging administrative offices and the box office.

Because of additional damage from Katrina and the limited availability of original architectural drawings, the theater owners contracted 3D Laser Imaging to prepare an as-is digital model of the existing structure that could be used to plan and facilitate renovations. This seemingly straightforward request soon morphed into the need for a 3D model with interior and exterior decorative detail–all on a limited budget.

A combination of laser scanning and orthographic images created from the laser-meshed data provided the perfect solution.

Developing a Deliverable
To develop a comprehensive renovation plan, the Saenger Theater owner requested an accurate Autodesk Revit 3D model as well as scanned images for use in the free Leica TruView software. The measurable, scanned TruView images would provide the owner and project team with additional detail that may not be in the 3-D model.

Over the course of three days, 3D Laser Imaging’s two-person crew set up in 240 different scan positions inside and outside the theater. There were 6070 scan positions on each floor and 30 scan positions in the basement. The scan team chose to use cloud-to-cloud registration techniques, as opposed to georeferencing the scans to a survey control network, since there was plenty of overlapping detail. Each scan position produced one or more gigabytes of data in raw form.

Overall, the team produced over 500-gigabytes of raw scanned data.

With that much data, the challenge is to extract the correct amount of detail from the point cloud without blowing the budget. Initially, we were just supposed to shoot the inside/ outside shell of the structure, but then the owner asked if we could also detail the decorative dcor and detail on the interior wall faces.

In response, the 3D Laser Imaging laser scan team used the point cloud data to create a shell model of the interior and exterior of the theater. We further used the scanned data to create orthographic .tif files

Orthographic images are a common deliverable in the architectural community, commonly used by architects within the CAD environment to trace or re-design. For a rehabilitation project, it’s not always apparent what the owner, architect or project team will need. In some cases, they might only need to illustrate the structural details, not necessarily reconstruct. That’s where the orthographic images proved invaluable. The scaled .tiff orthophotos can be used in the same way–as a backdrop for laser scanned point clouds or to help define decorative detail within the 3D model.

For the interior wall surfaces, 3D Laser Imaging imported the orthophotos as background to the laser scanned data within Revit and traced the details requested by the client as needed.

Lessons in Lasers
In the case of the Saenger Theater, the client initially asked for a measurable 3D model of the structural shell, interior and exterior. As the model data began to emerge, the owner and architect found they needed greater detail.

Scope creep is a common occurrence on a project. It’s imperative that survey professionals ask the right questions so that clients can clearly define what level of detail they want from a laser scan. Create a checklist during the planning phases.

Also, define the registration technique up-front. Scans of structures such as the Saenger Theater showed enough detail to use the cloud-to-cloud registration and kept the cost of registration down. Other projects will require survey control, design coordinate control or both.

In some cases, the client might not need a 3D model. The level of detail required is tied to the purpose of the data. In some cases, a 2D footprint will do. Identify the level of the data, so that the scan team can gather the proper detail in the appropriate format.

It is a learning process on both sides to provide the necessary detail within the budget. The difference between a 2D footprint versus an intelligent 3D model can be the difference between a couple hours or days and a few months.

Laser Advances
For the Saenger Theater, 3D Laser Imaging used the Leica HDS 6000 from Leica Geosystems. The firm has since upgraded to the more advanced Leica ScanStation C10 from Leica Geosystems for its range and functionality.

Laser scanning tools continue to get more affordable, flexible and powerful. I would have cut my workload by 35% on the Saenger Theater if I had the C10 range and functionality by cutting setups from 250 to about 150–150 scans versus 250 scans makes a big difference in managing data.

For instance, 3DI Laser Imaging developed an as-built 3D model using orthophotos and laser scanning of a 15,000 sq ft Victorian-style city hall in Yuma, Arizona. Originally built in 1921, the structure has a significant amount of detail that the owner wanted to repair or replicate. This time, the laser scan team used the Leica C-10. We completed the entire scanning effort, interior and exterior, in six hours with just 75 setups–about one-half as many scans as we would have needed using older phase-based scanning systems.

The newer scanners such as the C-10 are also able to capture greater detail at longer distances and a more streamlined interface with the post-processing software. Therefore, the data that’s gathered is more manageable with fewer setups and much faster scan-to-model capabilities.

The firm used Leica Cyclone 3-D point cloud processing software to manage most of the point cloud data and Leica CloudWorx to translate data into Autodesk Revit. Using 3-D laser scanners to capture a structure’s surface with engineering accuracy ultimately produces a highly accurate and measurable as-built model.

With the increased demand for renovations and reuse, laser scanning provides owners and project teams with accurate, comprehensive as-is conditions. I believe we’re in the midst of a huge paradigm shift in the way we use laser scanning. It’s valid currency in the data exchange market.

In the BIM environment, laser scanning is one of the few speedy, accurate ways to gather as-built conditions on existing structures. In some cases, such as the historic Saenger Theater in New Orleans, Louisiana, it’s the only option.

*The Saenger Theatre is now owned by the Canal Street Development Corp. who leases the building to the Saenger Theatre Partnership, Ltd.

Dietrich Evans is the CEO and Founder of 3D Laser Imaging.

A 678Kb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE