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UAV and Direct Georeferencing (DG) solution x RTK

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/23rd February 2019, Joao Marcelo Correa, Drone Market Watch™/ The startup Novarum Sky presents a new solution for Direct Georeferencing (DG) for use in fixed or rotary wing drones to enable Georeferenced Maps with very high accuracy and precision, better than 5 cm. But before explaining about the DG Novarum Sky solution, do you know the difference between DG and RTK or PPK? 

They are different techniques. In summary, it can be said that DG uses RTK or PPK technology to determine Drone's position at the moment of recording the photo, but this is not enough to make maps with precision and centimeter accuracy without the use of ground control points (GCPs). In PPK or RTK, UAV position calculation is done periodically and depends on the satellite data acquisition frequency on the Rover GNSS receiver installed on the UAV, so a 20 Hz GNSS receiver calculates the position of the UAV with centimeter accuracy at every 50 ms.

The time of 50 ms seems little but a Drone flying at 10 m/s in the horizontal direction travels 25 cm in 25 ms, so in this case the average error of the Drone's position at the moment of the photo will be 25 cm, so the accuracy of the map will be decimetric. In order to obtain a Georeferenced map with centimeter accuracy using only the RTK or PPK techniques, it will be necessary to use GCPs for later use in the photogrammetry software that corrects the coordinates of the photos to the centimeter level. The lower the frequency of the GNSS Rover receiver and / or UAV high flight speed, the worse the accuracy of the RTK or PPK solution. The DG solution normally saves 50% of the on-site work time and 50% of the map processing time, because GCPs are not necessary and the lateral overlap of the photos can be only 40% and longitudinal 60%.

In the DG technique it is necessary to estimate the position of the UAV at the time of acquisition of the photo independent of the GNSS Rover receiver frequency and the flight speed. Current DG systems use PPK or RTK techniques and perform algorithms for more accurate position calculation through data generated by the IMU - Inertial Navigation System. In general, the IMU operates at the frequency of 100 Hz, so it provides data every 10 ms to calculate the estimated Drone position. These DG systems also require additional software, proprietary boards that integrate the GNSS Rover L1 / L2 receiver into the IMU, and the cost can exceed the cost of the UAV solution.

After three years of research and development, Novarum Sky has developed an innovative DG solution that does not use proprietary hardware, but running RTK or PPK solution on Raspberry Pi, GNSS receiver L1@5Hz configured to receive Raw data from three constellations and new software that corrects the position of the Drone at the time of exposure of the photo with sampling frequency of 2000 Hz. Novarum Sky DG does not use IMU, however it provides the coordinates of the photos with accuracy and precision better than 5 cm at the end of the workflow without the use of GCPs. Another important factor is the time to FIX RTK that in the DG Novarum Sky solution is only 3 minutes. The base GNSS receiver can be accessed via Internet with the NTRIP protocol or locally for the RTK or PPK solution.

If you want to know if the manufacturer's DG solution works to make georeferenced map with centimeter accuracy, it must provide a georeferenced map report made by first-line photogrammetry software. In the report you must inform at least: 1) that GCP was used only to verify the accuracy of the position of the photos and 2) the RMS Error X [m], RMS Error Y [m] and RMS Error Z [m], all RMS Errors must be under 10 centimeters.
For example, Novarum Sky made a geo-referenced map using EtheCopter DG system on a Mikrokopter Hexa Drone flying at 8 m/s, Sony HX60V camera, connection with GNSS Base via NTRIP-Internet, three GCPs for verification, and Pix4d's photogrammetry software. The results were a georeferenced map with GSD of 1.05 cm and RMS error at coordinates X = 3.20, Y = 3.26 and Z of 3.47 cm. See the report prints:

UAV and Georeferencing2


During the months of March and April 2019, Novarum Sky will sell twenty units of the DG at a promotional price of US$ 1,500.00 plus shipping cost to companies to evaluate that are interested in providing the solution to the market in O&M or resale. Included documentation and all necessary support. We will be very happy to attend. Please forward the request to the email: contact@novarumsky.com

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In this article is used information and pictures from: Direct georeferencing on small unmanned aerial platforms for improved reliability and accuracy of mapping without the need for ground control points

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