Drones Earn Their Place In Surveying
Slashing the time and improving the documentation needed for site development surveys is what any survey firm wants. Tools such as total stations and laser scanners certainly get the job done, yet they also require extensive time to set up and move around as the surveyor walks through the site.
Now, drones — or UAVs (unmanned aerial vehicles) as they are often called — are steadily being adopted as a serious method to rapidly collect huge chunks of data accurately versus traditional surveying methods. A UAV can acquire data faster from the sky in the form of geospatial images with high resolution. Data is often captured in the millions of data points in several short flights over a sizable parcel.
Once a UAV is launched and airborne — typically armed with a built-in camera and a map of the site to be surveyed — it photographs the land parcel and plots it to the map. When the UAV lands, the user downloads collected images and combines the images with either the surveyed ground control points or the UAV’s Real Time Kinematics (RTK) data into a photogrammetric software package. This process produces a high-resolution orthophoto (aerial photo geometrically corrected) of the site, along with a dense point cloud, which can then be imported into CAD software for further analysis.
Looking Beyond Our Borders for Lessons on UAV Use
Contractors in many countries, such as Canada and those in Europe, already are well established in using UAVs for surveying projects. But in the U.S., UAV use for this purpose has lagged behind while the Federal Aviation Administration (FAA) has worked to establish regulations on how UAVs are to be used commercially.
Meanwhile, surveyors in the U.S. can learn the benefits of using UAVs for surveying from many of their peers in countries where this kind of surveying occurs more freely. Bernie Jess is one such land surveyor, based in Edmonton, Alberta, and has been sending off UAVs to tackle large site development surveys for about four years. Jess thinks UAVs can be most helpful for surveying construction projects where, for example, huge amounts of dirt must be moved and measured. Part of the equation for this cost is how people get paid for the work they do, which he explain is typically on the volume of material they move around.
Traditionally, surveyors have been utilizing either conventional total stations or GNSS RTK techniques to acquire data required for these types of projects. This can be a time-consuming and tedious job. A 20-acre industrial site at the west end of Edmonton that Jess worked in 2012 involved performing a conventional survey with a UAV topo later on. The topo was done pre-construction, after which came the engineering design work. The next step involved stripping off the topsoil and a shaping on the clay underneath. This is where a lot of the volumes of dirt had to be removed. The last step was to put the topsoil back on the clay and finish the lot.
All of this survey work required tremendous walking back and forth, Jess recalled, which is why he decided using a UAV was significantly more efficient for accomplishing the survey of his site. Photogrammetry was employed with the UAV to create a surface model, and then make volume calculations.
One Million Points in 15 Minutes
To perform his survey, Jess used a survey-grade UAV system called the eBee, which is made by SenseFly of Lausanne, Switzerland. The UAV is capable of receiving data corrections streamed from a base station or vertical reality simulator to achieve absolute X, Y, Z accuracy of down to 1.2 inches without requiring ground control points.
The eBee can cover up to 4.6 square miles in a single flight. It is supplied with two software packages: eMotion (flight planning and control) and Post Flight Terra 3D (professional photogrammetry). Once Jess has collected the data he needs, it is downloaded from the eBee to MicroSurvey CAD Ultimate, a special surveying software program with point cloud technology offered by MicroSurvey Inc.
In place of doing a lot of footwork and gathering points every 5.5 yards, Jess is able to use his UAV, perform photogrammetry, create a surface model and then make volume count calculations of dirt removed. When the UAV has completed its flights, it shows a map of the land parcel with green symbols that indicate photographs it has taken. The photos are assembled in a complex mathematical procedure, Jess says. Next, the user can calculate the latitude, longitude, height or the northing/easting elevation of every object in a photograph.
“Depending on the scale and height of the photogrammetry, I can get a survey data point in that example every five centimeters (0.39 inches),” he explains. “If I were to do this surveying by foot, I could maybe get 500 to 600 points a day. This flight took about 15 minutes and produced somewhere around one million points.”
To survey the 20-acre development site with the eBee UAV, it took Jess roughly one-and-a-half hours to set up, establish ground control, program and upload the flight, and launch the UAV. It then took about an hour to pack up once the survey was completed.
A major advantage with using the eBee is that it can show the numerous phases of construction at the site Jess has surveyed. These include taking a raw piece of ground, reshaping and, ultimately, submitting a final plan. The UAV technology allows surveyors to document site construction properly.
MicroSurvey CAD Ultimate Keeps It Clean
The combination of technology tools that Jess uses — UAV, photogrammetry, point cloud and conversion of the point cloud data into a drawing — is what makes this new approach to land surveying compelling. The MicroSurvey CAD Ultimate is especially helpful, not just for processing massive point clouds, but also for managing details in a site drawing.
“MicroSurvey Ultimate allows you to delete things you don’t want when trying to contour a surface in order to calculate dirt volumes,” he says, “and to find out what elevations are on that surface.” This means there might be a truck and a tractor in the UAV-surveyed images, and “I want to remove these objects from my surface and deal with a bare surface model.” Using MicroSurvey Ultimate, Jess simply draws a grid box around an unwanted item and collects the point cloud for it. The point cloud shows points randomly hovering in the air, which Jess can then cut out.
Another plus that Jess sees in using the drawing software is that it can move back and forth between the point cloud and CAD program. “I can work with and manipulate the point cloud,” he says, “then I can move back into CAD to create the final deliverable.”
MicroSurvey CAD Ultimate also offers filtering techniques. As an example, a surveyor can pick up the lowest point in a development site and reduce the point cloud by “windowing” certain areas that are known to be fairly flat. “This makes it possible to, say, take 10 million points and filter them down to a more usable number,” Jess says.
The result of this new approach to surveying is that engineers now can see a visual documentation of their survey project along with the surveyor, because of the multiple flights and massive data collection accomplished through use of a UAV. “The selling point here is quality, how quickly this surveying method can be done, the extra imagery you get, and the documentation that can be done that you don’t see with conventional surveying methods,” Jess says. “I can send all of this (the completed 3D drawing) off in Google Map Tiles to a client who can see the details of the complete survey without requiring the MicroSurvey CAD software.”
The Bottom Line is The UAV Makes Sense
Still another big factor in favor of UAVs is the cost savings, according to Reid Demman, PLS, immediate past president of the U.S. National Association of County Surveyors. Although the purchase of a survey-grade UAV can range $50,000-$70,000, it can cost $10,000-$40,000 to hire an aerial photography firm to fly over just one standalone survey project such as the 20-acre site Jess surveyed, notes Demman, a surveyor with the Salt Lake County Surveyor’s Office in Utah.
The Salt Lake County Surveyor’s Office is just one of several surveying entities that were eagerly awaiting FAA approval to use UAVs for a broad spectrum of survey projects. The wait was frustrating, especially since hobbyists by comparison had no restrictions on using UAVs as long as the devices were used below 400 feet. In the meantime, commercial applicants could meet certain criteria and regulations to obtain a Certificate of Authorization (COA).
Regardless, the wait will be worth it, Demman feels. “If you can send your own drone out to cover a wide survey area, you can gather the information you need in less than a day, compared to traditional survey methods that would take days and possibly weeks to compile survey data,” he says. “And you’d never have the density of data you’d get with the survey flights. The data you get with UAVs is more intense and dense, and the photography that comes out of these is spectacular.”
Needing to Survey Hard-to-Reach Spots?
Additionally, not every site that requires surveying has easy access or is safe on which to walk. The Salt Lake County Surveyor’s Office must measure hazardous waste sites and landfills because these sites are regulated on the quantities of hazardous waste they are allowed to contain. The office uses scanners, but surveyors have to set control lines and occupy several different parts of these sites.
“Even though we can scan these stockpiles, it’s problematic because we still have to get out on the sites,” Demman explains. “It takes time.” As an alternative, “We could fly a UAV over these sites in minutes and have a much denser point cloud, and never have to go out to a site and interfere with equipment that may be operating on it.”
Another project for which Salt Lake County sees a promising use for UAVs is the Jordan River, which is about 51 miles long and flows northward through Sale Lake Valley. By flying a UAV over this stretch of land and river, for design purposes, the county surveyor’s office could collect cross-sectional data on the river and banks. “We could send the drone down the meander line of the river versus manually having to go out and take measurements,” Demman says. “We’d have photographs and spatially-accurate data for modeling and design.”
A big part of the Jordan River survey project is aimed at seeing how to build a trail system for bikes and hiking, which would help control flooding. “We need to know the limitations of this design effort and to know property ownership, slope analysis and many other aspects, which UAV surveying could provide.” Salt Lake County has several partners interested in using UAVs. These include the fire authority, police, parks department and flood control unit.
While surveying is a key application that Demman sees for UAVs, he cites disaster management as another huge potential application. “A UAV can be especially helpful for surveying disaster areas that can’t be reached, such as for floods, mudslides, hurricanes or earthquake damage, and for wildfire assessment,” he says. “In many cases, you need to know where the boundary lines are.”
In the case of a wildfire that has been deliberately set, property owners on the area set afire would be charged for the damage, Demman notes. This means that property owners would need to be identified, requiring the need to identify the spatial location of the fire as it pertains to properties. “That’s where the surveying aspect of a UAV comes into play.”
When the Job's Large, A UAV is the Answer
The benefits of using survey-grade UAVs for surveying large parcels of land (those ranging 10-100 acres in size) cannot be emphasized enough. As surveying projects become more complex and more costly to complete, the desire among surveyors to use UAVs to accomplish these projects will only keep rising. Most clients for whom such surveys are implemented clearly see the value because the imagery generated in the final drawing is so powerful, and valuable to clients.
“You won’t get this kind of imagery and detail from a LiDAR system,” argues Jess, the Canadian surveyor who is using UAV technology for surveying routinely. “A point cloud is much more efficient than a ground survey,” he says, adding that the introduction of UAVs offers surveyors a new technique for cost-effectively and efficiently acquiring data for medium- to large-scale projects that require surface models, such as mine sites, quarries and construction sites with earthworks.
UAVs as well as photogrammetric and point cloud software have matured to a level now where they have become a workable, everyday solution for surveyors. While airspace regulations and safety concerns have slowed adoption of UAVs and limited their use in some cases, where surveyors are able to use a UAV makes it the best tool for the job, Jess affirms. “But there are other advantages,” he says, noting cost and safety. “And there’s a documentation advantage, because you have aerial photos showing what was done and not done on the development site.”
That kind of information is powerful and helpful to both the surveyor and the client.