Drone LiDAR Detects High and Low Banks for a Boundary Survey
If you've watched Down to Earth: Beyond Boundaries, then you might be interested to take an interactive look at the point cloud created from data collected in the southern hills of Bastrop, Texas. This data was collected using the mdLiDAR1000 flying at a speed of 4.5 meters per second and an altitude of 50 meters. Click the image below to go to the point cloud viewer.
“Down to Earth” is the surveying reality series from Microdrones that shows how real surveyors collect data and turn it into real deliverables, despite challenging conditions, rugged terrain, and possible dangers.
In these episodes of Down to Earth, the team at Carlson, Brigance & Doering, Inc. (CBD), a civil engineering and surveying firm in the Austin Texas area is using drone LiDAR to create updated, accurate Boundary Surveys. For this project, they needed to survey a challenging, 550 acre, tract of land in Southern Texas, where the property boundary follows the Colorado River, which has changed significantly since the original survey from the late 1800s.
“Collecting the lidar data will allow us to generate these high banks and low banks and any of the other terrain features we’re having to deal with in order to create a boundary on this project,” Aaron Thomason, R.P.L.S. and Vice President at CBD explains. “There’s also some drastic elevation changes in the topography along the river. So, it makes much more sense to use a drone that’s 50 meters in the air to collect the data, rather than introduce some hazardous terrain to climb.”
LiDAR above the Colorado River
Aaron sends UAV Pilot and GIS Specialist Laura Brown, into the field to collect the data surrounding the river using the mdLiDAR1000 from Microdrones. The system combines a fully integrated SICK LD-MRS4 paired with a FLIR 5MP Global Shutter camera. In addition, the system uses an Applanix APX-15 UAV, a compact single-board module with survey-grade GNSS receiver and a precisely calibrated IMU for mapping.
Data from the Point Cloud
The data for the point cloud was captured over 550 acres of steep banks, muddy terrain, and rushing water, make this a very challenging and lengthy project for conventional surveying. Laura chose to fly the area vertically, instead of horizontally to conserve battery power.
Using mdCockpit she planned 4 flights and used the terrain follow feature to be sure to stay above the tree line and account for the 11 meter difference in height between the banks of the Colorado River. The drone flew at an altitude of 50 meters and a speed of 4.5 meters per second. The duration of each flight was approximately 17 minutes completed in 49 legs with 60% overlap.
To create the point cloud, the data from Beyond Boundaries was first processed with mdInfinity Trajectory Processing and Georeferencing modules. Then further processing in mdInfinity was conducted which allowed for precision enhancement, removing outliers, and ground classification.
Using data collected from the point cloud, CBD was able to deliver a completed and certified ALTA survey for their customer.
“We flew the Microdrones system to collect the data along the Colorado River and did traditional surveying along the other boundaries,” Thomason said. “The final product was a signed and sealed survey where we found some differences from previous boundary solutions and our client lost almost 5 acres of land. But I’m very comfortable with the solution that we provided. We did our check shots to make sure high banks shots were accurate and our elevations were matching with the mdLiDAR1000 and everything was spot-on, right where it was supposed to be. So, I’m extremely happy with the data.”
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