Beyond Buildings and Bridges - 3D Mapping for Municipalities

Michael J. Carter, LLS

The information contained in this article is not intended as legal advice and may no longer be accurate due to changes in the law. Consult NHMA's legal services or your municipal attorney.

When a new technology provides a completely revolutionary way to do something, and it catches on, you can bet there are good reasons for it. For example, we can all think of many reasons why the use of airplanes as a mode of transportation caught on. In that same vein, a revolution is taking place in the surveying, architecture, engineering, and construction industries, and there are a great many good reasons why it is catching on quickly. That revolution involves a complete paradigm shift in how features are inspected and surveyed, designs are created, and construction is executed. Every town planner and municipal official responsible for making decisions about staff safety and/or infrastructure improvements would benefit from becoming more familiar with this emerging technology.

Today, in addition to conventional “boots on the ground” surveys using a total station and a variety of prisms, measurements are often performed with high-resolution 3D laser scanners and/or with high-resolution photogrammetric mapping from unmanned aerial vehicles (UAVs). These technologies quickly and easily acquire measurements and high-resolution images on features that are extremely difficult or dangerous to reach with conventional measurement devices. Laser scanners and UAVs also capture these detailed measurements and images without the need for a person to physically touch the surfaces of the features being measured. The implications of this for keeping personnel out of harm’s way cannot be overstated.

Many 3D laser scanners used today for exterior surveys have ranges of 1,000 feet or more with measurement accuracies of around 1/8 to 1/4 of an inch. They perform measurements at rates of up to 1,000,000 measurements/second. This allows surveyors to capture incredibly dense, super-accurate measurements on features safely (think of tall municipal buildings, dam faces, bridge components, features around high-voltage lines, etc.). These millions of laser measurements collectively produce a “point cloud”, which is a rich three-dimensional representation of the features that the scanner’s laser beam reflected back from during the course of each scan. An example is shown below:

Many commercial UAVs come fitted with a high-resolution digital camera system. These can capture high-resolution imagery for inspection or mapping uses in areas that even the 3D laser scanner can’t reach. An example of an image a UAV obtained of the top side of the Exeter water tower is shown above. In addition to their obvious “a picture is worth a thousand words” benefit, the digital images can be combined using specialized photogrammetric software to create a point cloud that can be used for making measurements. While these photogrammetrically-generated point clouds are typically not as dense or as accurate as those generated by a 3D laser scanner, they provide exponentially more data than would be gathered by a conventional instrument survey.

While UAV’s have been around for some time, their commercial use has been authorized by the FAA only since August 29, 2016. Municipal officials should be aware that for any commercial use of a UAV (e.g. for inspection of a tall tower, etc.) the FAA requires the UAV operator to be certified as a Remote Pilot In Command (RPIC). There are also regulations restricting the commercial use of UAV’s within the airspace surrounding certain airports.

Surveyors who use these two technologies eliminate for themselves and their clients the cost and delay of bringing in lifts or other equipment to access difficult-to-reach places, and get far more complete data than conventional processes allow. All of this is done without ever putting personnel in harm’s way.

For example, it is no longer necessary after a major flood event to send employees or contractors out onto unstable washed-out slopes or into run-off ditches to perform the inspections and surveys that are so urgently needed before designs can begin for repairs of roads and bridges, etc. In a typical 30-minute flight, a UAV can safely capture far more detailed measurements over a significantly greater area than several conventional survey crews could hope to capture in a full day of work. The UAV pilot and the associated GPS survey team can provide a rapid response and perform all their measurements while staying on the available safe dry ground.

As another example, it is also no longer necessary to send personnel up on tall ladders or expensive man-lifts to perform inspection and measurements on steep rooftops or towers. These things can be done quickly, safely, and far more effectively with a 3D laser scanner operating on the ground and/or a UAV hovering near the subject of interest. 

These new technologies offer great benefits in addition to personnel safety. It is commonplace today for a school building or wastewater treatment facility to be surveyed inside and out using high-resolution 3D laser scanners before designs for renovations or additions move beyond initial concept stage.  Once such a laser-scan survey has been done on a building (or bridge, or dam, or any other structure) architects and engineers have an extraordinarily detailed, highly accurate image or model of the structure to use as the basis for their designs, and contractors benefit from the certainty of these measurements as well.  After making a modest investment in the scanning survey at the very start of the project, the town continues to harvest benefits throughout the project life cycle because contractors do not need to price “uncertainty” into several components of their bids. Another immediate benefit is that having a complete data set about the building virtually eliminates the long-standing nightmare of contractor “change orders” that amount to blank-check writing by the Town officials once the project is already underway. How many times have officials heard “My bid was based on the assumption of X, and once we got into that space we found Y, so that will require a change order in the amount of $$$$$?” If the surveyor with a laser scanner made a detailed 3D map of that space beforehand, everyone involved would have full knowledge of “Y” and the architects and engineers will have already planned for it while it was still inexpensive to do so.

Surveyors, architects, and engineers are also finding great value in the 3D laser scans and UAV photos because they very often prevent the need for a return visit to a site for additional measurements. This is because the 3D laser scanner and UAV camera almost invariably captures far more data than a client envisioned the need for when they developed the original request for the survey. For example, a 3D laser scan survey intended to capture measurements on the bell tower of a town hall will likely also capture the slope and square footage of the entire roof, the location and height of all electrical and communication lines in the vicinity of the building, the height above ground of the window sills, the height and location of every tree in the vicinity of the building (so if the tree were to fall, we would know whether or not its upper branches would reach any part of the building), etc.

As with so many new technologies, 3D laser scanning has gained widespread acceptance in the marketplace and now the hardware prices have declined while the hardware and software capabilities have improved. Advanced training and education is required to use this survey equipment properly, and is even more critical to perform careful analysis of the data collected and verify that the results conform to jurisdictional survey standards. It is no longer a “big deal” to have a surveyor come out to do a 3D laser scanning project on some valuable pieces of infrastructure. Instead, it is becoming routine, and municipalities are reaping the benefits. Just as towns and cities large and small have been adopting GIS for the last decade or so with tremendous benefits for planners and the public alike, they will soon be organizing and managing public infrastructure in Building Information Models (BIM) that help organize, communicate about, and plan for maintenance and improvements to public buildings. For new buildings, the BIM will begin with the architects and engineers who design them. For existing buildings, the BIM will begin with surveyors who create accurate 3D models of the existing structures and components.

Use of these technologies has applications far beyond buildings and bridges. Some routine examples are performing stockpile volume calculations. Let’s say a town is purchasing large quantities of sand or salt for winter roadway use. If the payment is based on the volume of material delivered, and the town wants something more accurate than counting truck loads hauled to the DPW yard, a surveyor offering UAV services can quickly provide an accurate volume of a pile (or series of piles) without ever sending staff climbing up onto it.

Here in New Hampshire, where 72% of our municipalities have a resident population of 6,000 people or less, this technology may seem better suited for larger towns and cities. The truth is that these benefits apply to municipalities (and projects), both large and small. There are abundant reasons why these technologies have caught on, and benefits like safety, efficiency, accuracy, and cost-savings are appreciated wherever one can apply them.

Michael J. Carter, LLS, is Director of 3D Mapping at Doucet Survey, Inc. Michael can be reached by email at or by phone at 603.614.4060.