Tower Accuracy: using Ground Control Points

Tower Accuracy: using Ground Control Points and RTK to Deliver Accurate Tower Heights

15 Mar 2023 Written by Sharon

Drone-enabled data has been a game changer for the Tower industry, in many instances eliminating the need for field personnel to climb a tower for inspection or survey.  Commercial, off-the-shelf drones combined with vHive’s platform ensure clear and consistent data that adds value throughout the organization, from M&A surveys to better billing and customer relationships.

When it comes to calculating the exact height of a tower and the equipment installed on the tower, though, most commonly used drones alone can only get “close enough” data – sufficient for visual understanding of an asset, but not for reporting to regulatory authorities.  The drone’s height accuracy is largely constrained by its hardware limitations. Specifically, the GPS accuracy is very low, and the barometer is affected by weather conditions, resulting in an overall poor height accuracy. When fed into the photogrammetry engine, this results in subpar height scaling..  With zoning, permissions, and licensing often dependent upon tower heights, however, an accurate measurement is sometimes critical.

Can Drones Deliver Accurate Tower Heights?

While most commercial drones can only get “close enough,” that doesn’t mean that the only solution for accuracy is to buy an expensive drone or send field personnel up a tower to measure it.  There are two common methods for achieving accurate heights using drones: ground control points (GCPs) and drones equipped with real-time kinematic (RTK) capability.

Tower Accuracy: using Ground Control Points
Ground Control Points

Advantages:

  • Sub-centimeter accuracy
  • Can be used with any commercial-off-the-shelf drones

Disadvantages:

  • Users must have access to the ground surrounding the asset
  • Costly (10 Aeropoints are $8K)

GCPs are commonly used in photogrammetry to get more accurate 3D models that can be used for survey or legal purposes.  GCPs are visible marks linked with a precise geographical coordinate point: they enable accurate georeferencing.   With multiple ground points in the image that have a precise location and a defined distance between them, Identified Technologies says: “To put it plainly, GCPs allow the survey drone to obtain accuracy down to a sub-centimeter level, which is very precise.” The only disadvantage to using GCPs is that they must be placed on the ground, which may be problematic in areas that are very difficult to access, such as rooftops.

Tower Accuracy: using Ground Control Points
Real-Time Kinematic (RTK)

Advantages:

  • High level of accuracy
  • No need for placement of GCP in difficult terrain

Disadvantages:

  • Relies upon a strong and uninterrupted connection with the drone, not ideal in cluttered environments.
  • Requires a drone with RTK support

Drones equipped with RTK are the second commonly used means of achieving exact measurements.  RTK is a GPS correction technology, which corrects the GPS during flight by using a fixed base station that sends out data to a receiver.  Leading drone manufacturer DJI has developed several enterprise drones that carry an RTK unit.  Both the drone and the base station receive GNSS data from satellites: as the drone reports its positional data to the controller, the controller sends corrections based on calculations from the position of the satellite, position of the drone, and base station data.  The correction happens during flight, so there is no need for special post-processing to get the accurate georeferencing required for precise measurement. RTK systems work best in open areas, where operators can count on maintaining a strong connection with the drone.

Creating Precision Models “Automagically”

While the technology is sophisticated, getting precise measurements and accurate “ground truth” is easy with vHive’s AI-powered platform.  vHive supports both Aeropoints GCPs and RTK technologies.

Traditional, low-tech GCPs can require an entire team and significant experience and equipment to place them with survey-grade accuracy and later locate each marker and provide information to the photogrammetry process.  Aeropoints, however, are “smart GCPs” – equipped with solar power, GPS and wireless connectivity that minimizes the labor involved and ensures consistent, accurate results. Using Aeropoints, customers can simply upload data as usual and hit the process button: vHive’s AI identifies the location of the Aeropoints and seamlessly connects between GCPs and images.  It happens “automagically!”

We’ve engineered the vHive platform to accommodate a wide variety of technology solutions, so that our customers can use the best tools for their needs.  For engineering and survey grade data, customers can choose between using a less expensive off-the-shelf drone and investing in Aeropoints or investing in an RTK-equipped drone.

There are many benefits to drone data even without sub-centimeter accuracy.  The understanding of what really exists in the field, and the insights, reports, and improved processes that come from that understanding all add value throughout TowerCo organizations.  If your use cases require the precision that GCPs or RTK bring to digital twins, however, we’ve got that covered too: with integration that provides the ease of use that our customers have come to expect from the vHive platform.

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