Photogrammetry with Drones, Rope Access, and TPAS®

Photogrammetry is the practice of extrapolating spatial relationships from photographic imagery. While the concept of photogrammetry is centuries old, today’s powerful software quickly generates a 3-dimensional point cloud of any scene or object captured with a half dozen or up to several hundred overlapping digital photographs. Two recent projects illustrate very different applications for this technology in expanding what Vertical Access can do for clients in hard to reach areas.

Developing Background Drawings from 3D Imagery

Work on existing structures begins with accurate as-built documentation.   For most conditions survey projects in difficult-to-reach areas, we bring our industrial rope access teams armed with the Tablet PC Annotation System (TPAS®) to digitally capture data and photographs of representative and notable conditions.  TPAS® links each condition and photograph to a location on a pre-loaded AutoCAD drawing.

But what if there is no background drawing on file for use in the field? In the past our project teams have created background drawings from photographs taken from a boom or aerial lift, from neighboring buildings, or with other means of measurement (such as deploying VA technicians on rope with measuring tape).

VA drone pilots obtained mid-range imagery for the creation of a photogrammetric 3D point cloud, as well as close-range video to document the condition of the exterior materials.

Enter photogrammetry.  On a recent project, the main façade of a building could not be surveyed with an aerial lift due to site features, leading the project team to investigate the use of an unmanned aerial vehicle (drone) to capture close-range imagery of the façade conditions as well as photographs for use in the creation of scaled, detailed background drawings.

Vertical Access’ licensed drone pilots operated a DJI Phantom 4 Pro drone to obtain medium-range imagery for the creation of a photogrammetric 3D point cloud, as well as close-range 4K video for the conditions documentation of the structure. The field work was accomplished by a team of two pilots in less than two days and required only partial closure of pedestrian walkways to safely conduct the drone flights.

Back in the office, VA used Pix4D Mapper Pro photogrammetry software to generate the point cloud, textured mesh, and 2D orthoimages (elevations) of the areas to be surveyed.

The orthoimages were scaled and placed as background images in an AutoCAD drawing, and fault conditions such as cracks, spalls, and displaced masonry units were annotated digitally using TPAS®. Condition quantities were extracted from the AutoCAD drawing into an Excel spreadsheet to facilitate repair cost estimates.

We inserted the new 2D background image into AutoCAD and annotated using TPAS® at our desktops from video stills and photographs.

A close-range visual inspection as well as image capture for photogrammetry was completed in much less time than it would have taken to inspect the façades and obtain hand measurements using an aerial lift. The field work was accomplished with minimal disruption to pedestrians.

Modeling Decorative Features of Historic Structures With Photogrammetry Restoration of historic decorative terra cotta, cast stone, or natural stone often requires extensive replacement of individual units. Erecting scaffolding for hands-on access to measure and remove existing units adds significant cost to project budgets. Vertical Access recently used photogrammetry to aid in a pilot project as an alternative option for acquiring dimensions of existing units.

Step 1 of photogrammetric software processing generates a sparse 3D point cloud.

VA technicians photographed a terra cotta spandrel panel and parapet, using existing scaffolding to gain hands-on and close-range access. The photographs were used to create 3D photogrammetric models of individual units, achieving a level of detail sufficient to be transformed into specifications for replacement units.
With VA’s demonstrated rope access capability, individual units or entire assemblies can be photographed and modeled without the need for scaffolding, yielding a cost savings for the building owner.

Step 2 adds additional points to create a dense point cloud.

Additional processing generates a realistic 3D textured mesh by connecting points in the dense point cloud and adding color values.

Dutch Reformed Church Earns Structural Investigation Project of the Year Award


Vertical Access and Ryan Biggs | Clark Davis were presented this month with a Structural Engineering Project of the Year Award in the studies/investigation category for our Dutch Reformed Church Structural Investigation project by the American Society of Civil Engineers Structural Engineering Institute’s Mohawk Hudson Chapter. This was an exciting project for us and we were glad to be a part of the team!

Our role on the project included:

  • Documenting checks, levels and other representative and notable conditions at the roof trusses with digital photographs hyperlinked to annotated condition drawings with quantities provided for each condition using TPAS®.
  • Taking direct measurements of truss members to characterize the trusses and develop sketches of existing connection details.
  • Helping to determine the cause of movement observed at the roof framing.

More on this project

EVENT: Preservation on High: Investigation and Documentation of Monumental Historic Structures

Learn how available technological tools help to improve the collection and management of graphical and numerical information derived from building surveys.

dottyarrowLearn more and RSVP here.

DATE: June 11, 2015
TIME: 4:00pm – 6:00pm
LOCATION: Commons, 107 West Denny Way, Suite 303, Seattle, WA 98119


Preservation architects, engineers and others involved in the renovation of historic buildings agree on the importance of an efficient and thorough discovery phase. A significant part of that effort is the organized collection of building information and accurate documentation of existing conditions. Even though these discovery tasks are such a significant part of a project, the development and incorporation of tools to improve the process on site and process the resulting information has been slow to develop.

This presentation examines some components of a successful early discovery phase on monumental historic buildings and reviews some technological tools that help to improve the collection and management of graphical and numerical information derived from building surveys.


Kent Diebolt is the founder of Vertical Access and has been the principal-in-charge for most investigation, testing and inspection projects performed by Vertical Access over the firm’s 22-year history. Since the first Vertical Access project in 1992, Kent and his team have inspected numerous historically significant buildings, constructed of a wide variety of materials. He is an active participant and is a leader in professional preservation and rope access organizations.

Presented by Association for Preservation Technology NW and AIA Seattle Historic Resources Committee





Who is Buried in Grant’s Tomb? *

Grant’s Tomb is off the beaten track tread by most visitors to Manhattan. Photo credit:

Grant’s Tomb is off the beaten track tread by most visitors to Manhattan.
Photo source:

Once one of the most popular attractions in New York City, today Grant’s Tomb is off the beaten track tread by most visitors to Manhattan.  Constructed with the assistance of donations from 90,000 people totaling $600,000, the most money raised for a public monument at the time, the structure later suffered from neglect and fell into decline.[1]  Although it stands on a prominent point of Riverside Park overlooking the Hudson River, Grant’s Tomb is hidden in plain sight, with relatively few people venturing inside the mausoleum that contains the remains of President Ulysses S. Grant and his wife, Julia Dent Grant. 


 Grant’s Tomb was constructed between 1891 and 1897. Photo source: xxxx

Grant’s Tomb was constructed between 1891 and 1897. Photo source: National Park Service

Grant’s Tomb was designed by New York architect John H. Duncan and constructed between 1891 and 1897.  The exterior is based on the Mausoleum of Halicarnassus and the interior is modeled after the Tomb of Napoleon at Les Invalides in Paris.  On the exterior, the structure consists of a square base surmounted by a conical dome with a tall, colonnaded drum level, all faced with granite.  The main entry on the south side of the structure is distinguished by a wide plaza with steps leading up to a portico covering monumental bronze doors.  The ground floor has a large oculus through which the sarcophagi on the floor below can be seen.  Polished marble from Massachusetts is used for the interior floor surfaces and the railings, trim and dados at the walls of the ground floor and basement are clad with Italian marble.  The upper areas of the interior, including four barrel vaults facing the cardinal directions of the base of the monument, the pendentives where the square base transitions to the dome, the gallery at the drum level and the coffered ceiling at the interior dome, are faced with ornamental cast plaster.

The Grant Monument Association operated Grant’s Tomb until 1959, at which time the National Park Service took over management control and the site was designated as General Grant National Memorial.  From the 1970s to the early 1990s, visitors who ventured to Grant’s Tomb would find the granite walls of the monument covered with graffiti, the glass in the windows broken and the site in an overall state of disrepair.  Finally, faced with public criticism and a threat from the Illinois state legislature to move the remains of the Grants to their state, the federal government undertook much-needed repairs.  Following the restoration effort, the monument was re-dedicated on April 27, 1997.

Hands-on investigation of the plaster pilasters. Photo by Vertical Access.

Hands-on investigation of the plaster pilasters. Photo by Vertical Access.

As part of a site inspection of the General Grant National Memorial performed in 2012, National Park Service staff identified areas of cracking at the interior plaster at the drum level of the rotunda.  Some of the plaster at the pilasters at this area appeared detached.  The National Park Service requested the services of Vertical Access to perform a hands-on investigation of the plaster pilasters to better understand the causes of the cracks and determine whether the current condition presented an immediate public safety hazard.

As part of the investigation of the interior plaster, Vertical Access utilized several non-destructive and diagnostic tools.  As a first step, VA laid out the location of rigging holes in the coffered ceiling for the industrial rope access approach.  To locate the first rigging hole at the ceiling, a self-leveling laser level positioned on the ground floor was first used to establish the plumb line for the drop ropes in front of one of the pilasters.  To confirm which coffer was in line with the center of the pilaster when viewed from the attic side of the ceiling, the unfinished attic side of the coffer was warmed with a heat gun and the finished interior side was viewed with an infrared camera from the ground level.

 Conditions were documented using annotated drawings, still photography and video. Photo by Vertical Access.

Conditions were documented using annotated drawings, still photography and video. Photo by Vertical Access.

Once drop ropes were in place, Vertical Access technicians performed the hands-on investigation of the plaster pilasters, using diagnostic tools to better understand the construction of the pilasters and further investigate conditions of deterioration observed at the face of the pilasters.  A wall tie locator and rigid tube borescopes with a 0° (straight ahead) and 90° (right angle) direction of view as well as a 36”-long flexible tube borescope were employed during the investigation.  A video camera attached to the borescope unit provided recorded documentation of the subsurface conditions.  The cast plaster sections of the pilasters appear to be attached to the brick back-up structure with wood blocking.  Metal elements including wire ties and nails appear to have been used but no evidence of straps or anchors into the plaster was found.

 Conditions identified during the hands-on and close visual examination of the interior plaster were documented using annotated drawings, still photography and video.  At the conclusion of the investigation, Vertical Access installed crack monitors at two different pilasters.  Although the condition of the interior plaster does not represent an immediate threat to public safety, the crack monitors will be used to help determine whether the cracks observed are active.

* From Groucho Marx in the game show “You Bet Your Life”.  The correct answer is no one, since Ulysses S. Grant and his wife Julia are entombed but not buried in the memorial.

[1] Keister, Douglas.  Stories in Stone New York: A Field Guide to New York City Area Cemeteries & their Residents: Layton, UT: Gibbs Smith, 2011.  Page 142.

U.S. Capitol Dome to Undergo $60 Million Restoration

The Capitol Dome Will Get A $60 Million Face-Lift, by Eyder Peralta, National Public Radio, October 22, 2013

The U.S. Capitol Dome is about to undergo a $60 million restoration. Construction is scheduled to begin in November and last for two years.

“From a distance the dome looks magnificent, thanks to the hard-work of our employees,” the Architect of the Capitol Stephen T. Ayers says in a statement. “On closer look, under the paint, age and weather have taken its toll and the AOC needs to make repairs to preserve the Dome.”

Ayers says this will be first time the dome will receive a complete makeover since the one it received in 1959 to 1960.

The kind of damage that plagues the Capitol Dome.

The dome was constructed of cast iron more than 150 years ago. As time went on, water infiltrated through pinholes in the Statue of Freedom and through cracks and open joints in the rest of structure, causing rust and claiming more than 100 decorative elements. Currently, the dome has more than 1,000 cracks and deficiencies. These pictures give you an idea of the kind of damage we’re talking about.  *    READ FULL ARTICLE

* Photos in the Architect of the Capitol Flicker gallery are from a condition inspection report performed by Vertical Access. See project profile.

Scaffolding to Cover Capitol Dome, by Brian Williams, NBC Nightly News, October 22, 2013

20 seconds into the video, see footage of Vertical Access team on the dome.

Screen shot of NBC video coverage of U.S. Capitol Dome restoration project includes Vertical Access team performing inspection of conditions.

Screen shot of NBC video coverage of U.S. Capitol Dome restoration project includes Vertical Access team performing inspection of conditions.

Vertical Access Inspects Wyoming Capitol Dome

By Trevor Brown, Wyoming Tribune Eagle
CHEYENNE — A team of specialized engineers and technicians dangled 140 feet from the ground Tuesday as they rappelled down the side of the State Capitol’s dome.

Equipped with tablets to record notes and take pictures, three workers* from the consulting firm of Vertical Access went inch by inch, collecting data to determine the dome’s condition and the potential need for repairs.

Suzanne Norton is project coordinator with the state’s Department of Administration and Information. She said the work is the most detailed assessment of the dome in the Capitol’s history.  READ MORE

*Evan Kopelson, Keith Luscinski, and Berta de Miguel Alcalá

Documenting Historic Resources at the Tremont Nail Company

by Kelly Streeter

Tremont Nail Factory in Wareham, MA

Tremont Nail Factory in Wareham, MA

This past weekend I had the opportunity to speak to a Bachelor Design Studio class from Boston Architectural College (BAC) and demonstrate the documentation of historic resources using TPAS™.  Professor Johanna Rowley is directing her students in a case study at the 19th century factory of the Tremont Nail Company in Wareham, MA, a practical application of research and field work with real world implications.

Ms. Rowley first became aware of the site in 2011 while working on a BAC-funded project to investigate disaster recovery at restoration sites in the aftermath of the tornadoes that hit Springfield in 2011.   The site was purchased by the town in 2006 when Acorn Manufacturing moved the nail operation and has languished unused ever since.  Ms. Rowley’s goal is to mobilize her students and the community to help Wareham stabilize and document the site as an initial step in the effort to determine how the adaptation of the buildings and site could serve to fill existing needs of the community.

I met with Johanna and her students to discuss the goals of the site inspection.  The class had previously prepared background drawings from field measurements and archival data.  We then went into the field, with two separate teams working together with a TPAS™ kit to document and photograph the existing conditions at the site.  This information will now be used by the class to assess and prioritize the preservation needs of the site.

It was a fun day at an amazing landmark.  To follow the effort,  “Like”  their Facebook page.

Read article, Hammering out Tremont Nail’s restoration in Wareham

Register for TPAS Webinar Feb 26

Free TPAS Webinar
FEB 26, 2013 (Tuesday)
12:00 EST

Join us for an overview of the functionalities of TPAS including new and upcoming features. Q + A will follow.


TPAS software uses AutoCAD functions and formats you probably already know. It’s loaded into a ruggedized tablet PC linked to a digital camera along with project drawings letting you experience total digital inter-connectivity on site by entering graphical and numerical data, photographs and notes directly into your existing files.

And now, web-based TPAS report portals allow you to interactively search, view and format all project data and photographs within an internet browser.  You can create, edit and print reports from the browser without opening AutoCAD. This new feature  reduces the time and resources your project team spends on reporting tasks for complex, data-driven projects.

Vertical Access uses TPAS for existing conditions documentation, but its applications are as limitless as the reporting needs for your architecture, engineering or construction projects.

For morKelly-with-TPAS-CUe info:

Questions? Contact Kelly Streeter, PE at


A Visit to Canning Studios

by Kelly Streeter

I had the opportunity to visit John Canning Painting, Plastering and Conservation Studios in Cheshire, CT last week. Bill Barry, John Riccio and I met to discuss the application and customization of the TPAS software to the types of plaster surveys they routinely do. While there, I was able to tour the studio and get a sneak peak at the murals they are designing and executing for the Cathedral of St. Patrick in Norwich, CT. What a treat.

Transformative Technology – Tablet PC Software Modernizes Facility Condition Assessments

Chambers, Murphy and Burge Restoration Architects, are development partners for TPAS™  and have been utilizing the tablet-based digital annotation system in the field to document conditions and observations on their historic building restoration projects. In the article, Transformative Technology – Table PC Software Modernized Facility Condition Assessments, published in the October 2012 issue of  Properties Magazine , Michael Sanbury and Elizabeth Corbin Murphy describe how this technology has streamlined  their processes of assessments.

Learn more about this technology on the TPAS™ blog,  watch an on-demand webinar recording here, or contact Kelly Streeter, PE,  partner at Vertical Access.