GPS World

Tag: DJI Phantom 4 RTK

  • UAVs speed surveying and construction projects in United Kingdom

    UAVs speed surveying and construction projects in United Kingdom

    Screenshot: Propeller
    Screenshot: Propeller

    For a major project, surveying with traditional GPS equipment would normally take many days, Learn how Trimble and Propeller helped speed progress.

    Wills Bros, a family-run contractor based in the UK and Ireland, has begun work on the £29 million (USD $40 million) Maybole Bypass project in Scotland. The 6-km (~ 3.75-mi) project involves 900,000 cubic meters of earth removal and a further 15,000 cubes of rock that needs to be excavated and removed. In addition, Wills Bros is responsible for the construction of 10 culverts to deal with water flow in the area.

    For a project this size, surveying the entire site with traditional, ground-based GPS equipment would normally take six days, estimates Jonathan Wills, who was instrumental in the company’s recent investment in Trimble and Propeller equipment. But considering the increased accuracy tolerance required for some of the structural elements involving the culverts, getting useful survey data from the ground would actually take weeks for this project.

    As an alternative, Wills Bros is using Propeller PPK, a drone surveying workflow that combines DJI’s Phantom 4 RTK drone; AeroPoints’ “smart” ground-control points; offloaded data processing; and the Propeller Platform software that allows measuring of the site using 3D models generated from drone images. Wills Bros also is using Trimble Stratus for cloud-based drone survey processing, visualization and analytics with Propeller Platform.

    Wills Bros was able to collect an initial earthwork takeoff of the Maybole project area in a fraction of the time.

    “Savings on labor costs alone have been considerable given the fact that on so many occasions we can now obtain detailed project data within a second rather than sending a man on site to survey for information,” Wills said. “The drone comes in a backpack and is up in the air doing its thing within minutes. From the outset, the time savings are immense.”

    Once the drone and ground-control data are uploaded, Propeller transforms them into a 3D terrain model that can be measured in the cloud-based Propeller Platform.

  • Exploring Shetland’s uninhabited Kame of Isbister with GNSS and UAV

    Exploring Shetland’s uninhabited Kame of Isbister with GNSS and UAV

    The mysterious and fascinating Kame of Isbister is situated in Shetland’s north mainland near the North Roe. The location has been studied several times, including by the Extreme Archaeology TV series in 2003. The uninhabited grassland continues to attract explorers because of a series of secret structures.

    Those structures are hidden on the sea-faced slope and can’t be seen from the land nearby. One theory posits that it’s an eremitical monastery settlement. The late Pictish/early Medieval site is hard to access — and that’s where drones coupled with GNSS receivers helped explorers.

    In 2019, Shetland Flyer Aerial Media in collaboration with Shetland College UHI and the Institute for Northern Studies explored the site. Their goals: create a 3D model of the headland as well as an orthomosaic and digital terrain model to identify and map the monastery structures.

    Because the site is hard to access, the team decided to use the DJI Phantom 4 RTK SUA (drone and base) with two flights. One flight captured both the Kame and a piece of the mainland for context, with a ground sample distance (GSD) of 2.4 centimeters/pixel (cm/px). The second flight was on a shorter GSD of 1.9 cm/px to capture detailed pictures of the cape and structures.

    Before the survey, the team used the Emlid Reach RS+ real-time kinematic (RTK) receiver to identify and establish the base mark for the drone on the mainland nearby.

    Ground control point locations. (Image: Emlid)
    Ground control point locations. (Image: Emlid)

    The base mark was then post-processed using data from the OS Net reference station in Lerwick. Considering the long baseline (52 kilometers), it took the team four hours to observe the mark with Reach RS+. Later, when the archaeologists managed to climb the headland, the RTK receiver collected several noticeable control points.

    Creating the 3D model. During both flights, the drone’s base was sending corrections in RTK mode. In post-processing, horizontal accuracy of the processed map initially was within 10 cm with vertical at 15 cm. After adding the control points gathered with the RTK receiver, the error was reduced to 6.5 cm, significantly increasing the accuracy of the model.

    The team performed the GIS processing in QGIS 3.4 LTR.

    Screenshot: Emlid
    Screenshot: Emlid

    Despite the long grass, they managed to distinguish each structure out of the orthomosaic using the 32-bit floating point raster digital elevation model (DEM). The team created a basic map with structures and contours, a hillshade version and a heat map.

    With proper preparation and setup, a GNSS RTK receiver with a drone can gather enough high-accuracy data to create accurate models and maps of an archaeological site — even if it’s hard to reach.

    Shoreline contours and structures. (Image: Emlid)
    Shoreline contours and structures. (Image: Emlid)
    Shoreline contours and structures with hillshade. (Image: Emlid)
    Shoreline contours and structures with hillshade. (Image: Emlid)
    3D model: The heatmap of the Kame of Isbister shows elevations and the archaeological site. (Image: Emlid)
    3D model: The heatmap of the Kame of Isbister shows elevations and the archaeological site. (Image: Emlid)