Highest Accuracy in Photogrammetric Drone Mapping and Surveying – Systems You can Rely on!

The UAV market becomes more and more confusing, while at the same time the promises system manufacturers and service providers make are becoming  huge and sometimes really unbelievable.  Even the high price segment providers for professional drone systems make me continuously wonder: A short while ago, I looked at the website of a well known, regional drone company and had to read “image stitching” in the context of photogrammetry. Shouldn’t it be known amongst professionals that the accurate 3D arrangement of points (so called point cloud) results from aerotriangulation, the law of collinearity and it’s equations,  from the block bundle adjustment developed about 90 years ago by Carl Friedrich Gauß’s in conjunction with precise center of image coordinates and calibration data of the optical system used… it just has very little, or basically nothing to do with the development of nice panoramic images (photo stitching). Photogrammetry is and remains an engineering science, still worth while to get a master degree at a renowned university.

Lets get back to photogrammetry! As already stated in earlier blog posts, while choosing sensors (cameras), suitable drones, GNSS-technology, flight planning and photogrammetry software, a few basic but fundamental prerequisites have to be considered. More information can be found here.

This article is focusing on systems tested by KLAU Geomatics, Australia an by ourselves which we know that those systems are able to deliver final results, exclusively using direct georeferencing in the range of better three centimeters in all 3 dimensions. So far we have tested UAVs from DJI and those, equipped with a Pixhawk Flight controller. To make a long story short: As long as the use of the system only has to cover even terrain DJI’s Phantom 4 RTK (SDK version without integrated screen and base station) in combination with KLAU’s adopted KLAUPPK for DJI RTK drones software, using the specific DJI file structure,  is the most efficient and lowest cost solution.  The integrated 20 MP camera (pretty much identical with the the camera oft DJI’s Phantom 4 PRO (V2.0) as well as with the Zenmuse X4s) enables a GSD of less than 20mm at a flight altitude of 70 meters. In addition the camera shows a relatively low, but quite radial symmetric distortion, a very important feature in precise photogrammetric applications. Since PPK processing (post processed kinematic) does not need any real time correction like RTK systems depend on, this system always works, even if there is no mobile data coverage and does not need the DJI base station. Unfortunately there is no safe third party way point software like eg. UgCS for DJI (ugCS PRo from SPH Engineering) available, which would allow to fly in the terrain follow modus, essential for missions in hilly or even alpine terrain. Phantom 4 RTK is the only exemption. All other DJI systems – to our knowledge – can be operated through the advanced UgCS mission planning software. The most recent release (3.5.x) of UgCS has been released End of February. For only 535 € (excl. VAT) offers a variety of different planning tools for surveying, scanning and advanced facade mapping. In addition, custom no fly zones can be generated to secure missions and force the aircraft depending on the route parameters to change either altitudes or fly around the prohibited area.

The use of those NFZs are a great tool to design mapping or scanning routes with changing altitudes. A new (3.4) “Continue Rote” feature is a highlight not only for huge missions. If the pre planned route has to be left due to a battery change, the UAV will continue the mission exactly on the coordinate point where it has left. Generating double sets of imagery (this always happens if the miossion is continued at the last waypoint passed – often the startpoint on the beginning of a long flight line) is history and efficiency is increasing!

Now, let’s get back to reliable drones: A simple to use but versatile drone is DJI’s Matrice 210 RTK V2.0. As a suitable sensors you can either use the Zenmuse X4s (which DJI has stopped to manufacture and sell) or the Zenmuse X7 system camera with 24 or 35 mm lens). Again I’d like to stress the absolute need to have a global (mechanical) shutter camera for precise aerial photogrammetry. This is also true if your photogrammetry software provides features like “rolling shutter compensation” since even the software only can reduce a problem but not eliminating it as “shit in (is likely,) shit out”

Upgrading the M200/210 with a KLAUPPK GNSS system and a Sony camera is a great alternative to the M210 RTK V2.0. As optical systems the Sony A600 family has been proven as a very good choice (the A7R is a bit heavy and slow in data writing) as well as the Sony RX1R2  (The dedicated gimbal from Klau which mechanically fits onto the single DJI gimbal mount can be tilted in 15° steps from horizontal to nadir and is available for Sony’s A6000 and RX1RII. The camera is being triggered through the KLAUPPK system by preset time or distance intervals. If you consider to upgrade a M210 RTK (V1.0/V2.0) you need to consider detaching the RTK-antennas and mounts due to MTOW limitation.

Upgrading DJI’s multifunctional platform M600 with KLAUPPK is quite simple and straight forward. More important is the use of the camera and the gimbal. The camera can be triggered by the autopilot (way point route) or by the PPK system (using the time or distance preset function.

As alternative to DJI systems we have been very successful in testing drone systems with Pixhawk flight controller. For over one year we tested an AIR6 (from AIR6 SYSTEMS) equipped with a Sony A6000/SEL20F28 (20mm) and KLAUPPK in most different projects with excellent imagery and accuracy results of the end products (point cloud). For mission planning, ARDUPILOT Mission Planner was used and found very straight forward. In addition we also have tested connectivity and functionality of UgCS successful in our tests.

For comprehensive and in depth photogrammetry know how we offer seminars and trainings for professionals. Further information about KLAUPPK systems you’ll find here! We are looking forward to your email at info@videographics.de or your personal call +49 (0)81048889810. You are welcome to contact us for further information and support in the context of drone photogrammetric mapping!