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How you can achieve 1 cm (0.4 in) drone survey accuracy in your next mapping project

Drone PPK accuracy comparison infographThe recent Wingtra white paper on Reaching 1 cm (0.4 in) Absolute Accuracy showcases that the VTOL fixed-wing WingtraOne drone reaches three times higher accuracy than what other fixed-wing drones can achieve. But how does it actually work? And what do you have to do to reach such drone survey accuracy? Read further and we will guide you through the steps.

 

Use a WingtraOne PPK drone with a Sony RX1RII payload

WingtraOne PPK is the only broad-coverage drone to date to have achieved subcentimeter (0.4 in) absolute drone survey accuracy results.

VTOL drone with heavier payload and camera
The VTOL WingtraOne can safely carry heavy high-end sensors; for example, a 42 MP full frame Sony RX1RII. Such a camera takes really high resolution images with a higher number of total pixels. Since coordinates are defined for each pixel, the more of them there are, the more accurate the final map or 3D model is. Therefore, VTOL = higher resolution = better accuracy.

Be aware of the distance to a base station

The achievable absolute accuracy depends on the correction data derived from the static base station logging. The closer a base station is to the flight location, the better the correction data will be to the onboard GNSS logging of the WingtraOne.

PPK accuracy and distance to base station
Absolute accuracy results decrease gradually when moving away from the static base station. Rule of thumb — every 10 km (6.2 mi) add 1 cm (0.4 in) to the accuracy.

When using a continuously measuring GNSS station, make sure it is close enough. The accuracy results will reduce gradually the further you are from the station. Rule of thumb—every 10 km (6.2 mi) adds 1 cm (0.4 in) to the RMS error.

In case the GNSS station is further away, use your own base station.

Be aware of elevation influence

A long baseline most of all effects the vertical accuracy. In the case of a height difference between base station and surveying area of more than 500 m (1640 ft), accuracy becomes significantly worse. Take that into consideration when planning your projects.

PPK accuracy and elevation difference to base station
In case of more than 500 m (1640 ft) elevation difference to a base station, accuracy results will be worse.

Always use a high-quality, survey-grade base station

When setting up a new base station on an unknown point, let the GNSS receiver log the GPS data for a couple of hours or, even better, overnight. Logging GPS data for longer periods will help ensure higher accuracy results.

Note that if a new base station is established on a known point, the results depend on how accurately the point was measured before.

PPK and connection to base station
When establishing a new base station, log GPS data for at least a couple of hours.

Important! Don’t forget to check minimum base station requirements, which are:

  • Possibility of continuous logging with logging interval of 15s or faster (1s is recommended for highest accuracy)
  • Logging at least two frequencies L1 and L2
  • Receiving Constellations GPS + GLONASS (optional for high precision)

Establish checkpoints to prove the accuracy to your customer

When measuring your checkpoints, make sure to use an RTK or PPK GPS receiver. Common brands include Trimble or Leica. Using any device other than an RTK or PPK GPS receiver will compromise the accuracy.

Remember to place the tip of your GPS receiver directly on the center of the control point marker. Make sure to calibrate your GPS receiver to be level with the ground. Follow the instructions on the system provided by the measurement device manufacturer. Use a tripod to make sure the receiver is stable and does not move during the measurement process.

Checkpoints for PPK accuracy
To ensure bulletproof accuracy evaluation, make sure that your checkpoints are measured precisely.

Be careful with different coordinate systems

WingtraOne images can be geotagged in any Earth-centered, Earth-fixed coordinate system such as WGS84. In case a local projected coordinate system is desired as an output, the transformation can be performed either in the post-processing toolchain or externally using a conversion tool suitable for the desired coordinate system. Be aware that the final results in local coordinate systems are only as good as the provided conversion tools for the local coordinate system.

PPK coordinates systems
Transforming final results from one coordinate system to another might introduce some errors. Be aware that the final results in local coordinate systems are only as good as the provided conversion tools.

Avoid environmental obstacles

The GNSS satellite signals can be blocked by big obstacles such as tall buildings, mountains or trees. Therefore when using GNSS as a surveying method, carefully choose locations where the surrounding environment does not shelter your receiver from the satellite signals.

PPK accuracy and obstacles
Environmental obstacles might block the GNSS satellite signal to your GNSS receiver. Such interference would have a negative impact on your accuracy results. Be aware of that when planning your projects in valleys, canyons or next to tall buildings.

Access raw data of the tests

No high-coverage drone to date has ever been capable of reaching subcentimeter level drone survey accuracy, and many experts were wary of trusting new facts about the WingtraOne. Thus in order to verify them, Wingtra partnered with RDO Integrated Controls, one of the largest Topcon and the largest Wingtra distributor in the US, as well as ETH Zurich, one of the best science universities in the world (Topuniversities, 2018).

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Wingtra
Wingtra

Wingtra develops, produces and commercializes high precision VTOL drones that collect survey-grade aerial data.

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