Drones for Surveying

Using Drone LiDAR Technology to Create Accurate As-built Surveys

Spatial Data Consultants has become very adept at using drone technology to quickly turnaround high-profile projects with a tight timeline.

High Point University needed the geospatial consulting firm to conduct an as-built survey for the Panther Drive project, a new entrance that straddled athletic fields and led into campus.

The team at Spatial Data Consultants (SDC) considered their options, though it didn’t take long to figure out how they would complete the job.

“The client calls us and there’s a pretty critical deadline on this project, so we put our heads together and knew that the mdLiDAR3000 from Microdrones would be the right tool for the job,” said Fred Johnson, director of UAV services at the firm also located in High Point, North Carolina.

Trees that lined the roadway and traffic presented potential obstacles, though SDC had confidence they could get the work done after Microdrones helped the firm transition from manned fixed wing and helicopter aircraft to drone surveying systems.

Fred Johnson, UAS Crew Chief, prepares the mdLiDAR3000 as part of a drone surveying project at High Point University.

Getting UAS workflow off the ground

Mark Schall, chief professional officer at SDC, first reached out to Microdrones in 2017. How could they supplement their manned aircraft workflow? Working with Microdrones, they decided the mdLiDAR3000 system was the right tool that suited their needs.

“Microdrones was extremely critical in getting our program off the ground in 2018 and helped all of our staff at that time transition to the UAS workflow,” Schall said. He’s proud of the level of expertise and competence displayed by employees like Johnson.

No wonder High Point University turned to SDC.

“We decided to do a corridor mission because the main focus was the new roadway leading into the campus,” explained Johnson. “I expect all of the details needed for the as-built survey to be clearly visible in my point cloud and photography.” 

Preparations started the day before arriving on campus for the mission. For comparison’s sake, Johnson looked at Google Earth and found the imagery there to be outdated — emphasizing the need for a new as-built survey.

Working with experienced drove surveyor Robert Chrismon, PLS, Johnson went through the rest of his pre-mission tasks, including checking weather and making sure the flight path didn’t interfere with FAA airspace.

Microdrones was extremely critical in getting our program off the ground in 2018 and helped all of our staff at that time transition to the UAS workflow.

Mark Schall, chief professional officer at SDC

They used mdCockpit to create a flight plan for a corridor about 80 meters wide with two flight lines on either side of the pavement on the outer edges of the roadway, with a flight time of about 16 minutes.

MdCockpit is the industry-leading app from Microdrones that allows professionals to plan, monitor, change and control flights right from a tablet.

Johnson also scouted locations for ground control points to ensure project accuracy. They were ready for the drone to take flight.

“I’m really curious to see what we come across in the outdated imagery areas to see if there’s anything there that shows we’ve got to adjust the plan once we get into the field,” Chrismon said. “But it looks like we’ve got a solid plan, good weather and good airspace.”

Scott Deford, a geomatics technician, checks ground control at the project.

Precision is key

With partly cloudy skies and not much wind, the day of the mission brought fairly good weather. It was time to transport the drone to campus, assemble the components and get the machine in the air.

The mdLiDAR3000 was ideal for the project because there were a lot of hard surfaces, said Matt Rosenbalm, sales manager for the eastern United States for Microdrones.

“Precision is key, so the mdLiDAR3000 and all the different payloads that go with it — along with a high-resolution camera fully integrated into the system is able to produce some high-quality data sets,” Rosenbaum said.

The day started smoothly enough. The mission plan called for flying about 80 meters above ground level at a rate of about 5 meters per second. But Johnson soon found an unexpected challenge.

“The roadway was not shut down as we were told it was going to be. We shifted the mission a little bit to fly even further outside the roadway so we weren’t faced with the potential of flying over someone,” Johnson said.

He also had a colleague observe at the other end of the corridor so that person could help maintain a line of sight on the drone and keep watch in case of any unforeseen obstacles.

Fortunately, the flight went fine and only took 11 minutes to complete.

“Overall, the mission went great and I anticipate the data is going to check as well,” Johnson said.

Clcik the image above to view the As-Built point cloud from this project

Efficiently delivering accurate outcomes

Back at the office, it was time to process the data. Chrismon was eager to see how some of the newer structures not visible in the Google Earth image, utilities and newer landscaping around the roadway would be reflected in the deliverables.

Johnson started by pulling in the trajectory data. He knew there was a NOAA Continuously Operation Reference Station (CORS) nearby, so he used the publicly available CORS data as the base for the post-processing of the directory.

While waiting for the mdInfinity desktop software to geocode the raw LiDAR files, Johnson prepared the computer-aided design (CAD) file, using the control points that would be crucial for helping to tie together the LiDAR strips and serve as a check for the LiDAR.

“One of the first things we want to do when we get the LiDAR data … is to make sure it’s in the right place in space” by comparing the LiDAR to the control points, Johnson said. The comparison allows Johnson to make any strip adjustments, if necessary. The analysis confirmed what Johnson anticipated — the results looked great.

The visualization of the data set from High Point University

Ground classification was next on the to-do list. For this particular project, which looked at the as-built survey as relative to the roadway and surrounding features, getting everything down to bare earth — or classified ground — would provide a look at all the features on the ground important for the project.

A final check is to compare the classified ground to the control points, as well as generating a shaded surface based on the ground-classified LiDAR. Once again, everything looked good. To improve visualization, Johnson colorized the point cloud.

Using the data viewer in the mdInfinity desktop, Johnson took a look at the final colorized point cloud. The level of detail was impressive.

“You see the brick sidewalk, you see the asphalt and the curb in between the two, and the vegetation stands out. The signs and the light poles, too,” Chrismon said.

SDC even added a bonus deliverable to High Point, creating models of just the ground surface alone, and one that included above-ground features. Using stereo compilation allowed the creation of a CAD drawing that included contours and planimetric, to go with the LiDAR point cloud and orthomosaic deliverables.

The outcomes for the as-built survey exemplified the kind of success that SDC has had with Microdrones.

“A lot of clients want to see power lines. They want to see road signs and power poles. They want to be able to see all those features,” Johnson said. “We can always count on the mdLiDAR300 to pick up those features.”