Jan 14, 2018 - much detail (compare to centre image patch in Figure 3). Figure 5: Castle Landenberg, Obwalden, Switzerland, modelled from UAV images. 15 ...
Article
From Toys to Tools
Unmanned Aerial Vehicles
Unmanned Aerial Vehicles (UAV’s) have recently attained great attention. This article explains why this is so and decribes the wide range of users and applications. But UAV’s also have a number of disadvantages, which have to be solved in the future in order to establish a good transition from ‘toys to tools’. By Armin Gruen
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bama demands Iran goes back to 1967, when Schlueter return downed US offered his first system. Five year drone. Iranian engilater even a construction set neers will soon build an aircraft became available. The first professuperior to the American (drone) sional photogrammetric use was using reverse engineering” – newsreported by Wester-Ebbinghaus, paper headline of 14 December 1980 who used such system for the 2011. monitoring of the construction of the UAVs (Unmanned Aerial Vehicles), Wuppertal monorail. At those times of course, autopilots based on or more generally called UASs GPS/INS were not available, nei(Unmanned Aerial Systems), have ther were digital cameras. Since recently attained great attention. Figure 1: “Photogrammetric” UAV of the Institute of Geodesy and Photogrammetry, ETH Zuerich then many things have been further Both amateur model aircraft pilots developed and have made the sysand military drone users are showtems more powerful: More diverse ing increased activities, as eviplatform and propulsion technolodenced by various media reports. gies, use of digital cameras, inteSqueezed between both parties are the civilian professional users, those gration of GPS and INS for which apply these technologies in autonomous flying, stabilizer for order to solve their technical probprecise camera axis pointing, more lems. This domain covers a very flexibility in both flight pattern and picture taking, and fast processing wide range of applications: capabilities. Archaeology, architecture, Cultural Heritage, large scale local mapUAV’s today ping, 3D city modeling, change Figure 2: The Copter1B on a mission flight over a cornfield (application in Plant Sciences) Today we can choose between the detection in urban and suburban many different types of aircrafts: areas, cadastre, characterization of Balloons, airships, gliders/kites, fixed wing gliders, propeller and jet river and other landscapes, landfill surveys, landslide investigations, agriculture and forestry, natural and man-made hazards, geology, enviengines, rotor-kite, single rotor (helicopter), coaxial systems, quadroronmental and construction monitoring, search and rescue, traffic superrotors, multi-copters. Gas-, jet- and electro-engines are applied and vision and traffic accident recording, fire brigade crisis management, each comes with its own advantages and disadvantages. Finally the application conditions will dictate the kind of platform to be best used. crime fighting and coordination of police services, multimedia applicaIn general however, UAV platforms have, compared to other data acquitions and generation of video games, etc. The diversity of applications sition techniques and tools, a number of significant advantages, as: is already now enormous and ever increasing as time goes by. This is • Flexibility in sensor design and integration, data acquisition and one of the reasons why so many people try to get into this technology. flight pattern (navigation, flying height). The choice of the recording The other reasons are the seemingly ease of operation of such aircrafts camera can be optimized with respect to project requirements. Flying and the economic benefits which this technology offers. heights can vary greatly (usually we fly at heights above ground For an instructive overview of current activities in the UAV sector please from 50 to 400m) and thus image coverage and footprint (ground contact: “UAS. Unmanned Aircraft Systems. The Global Perspective. resolution) can be varied. Production of vertical, oblique and hori2011/2012, 9th edition. Blyenburgh &Co, Paris, France. 216 pages”. The publication contains contributing stakeholders, country overviews, zontal images from one platform is possible, and maybe even durcertification and airspace integration, feature articles and a reference ing one flight. This is the more important the more truly 3D modelsection. Although this publication does by no means show all current ing projects require multi-arrangement imaging. activities in this sector, it indicates the widespread interest which this • Use in high-risk situations. The lack of on-board humans allows for more risky flight executions. technology finds. It clearly shows the large amount of systems avail• Flight close to objects. Parts of objects, which are otherwise not able, their different designs and various applications. reachable at all or only by great efforts, can be recorded. The underlying technology is by no means new. The model helicopter
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Figure 3: UAV image from 325m above ground, showing the excavation site Pernil Alto, Palpa, Peru (Archaic Period) in its environmental context. Traces of looting of burial grounds are clearly visible. Figure 4: UAV image from 50m above ground, showing the excavation site of Pernil Alto, Palpa, Peru in much detail (compare to centre image patch in Figure 3)
• Some systems require an experienced pilot. This is not only for operating the platform, but also for reasons of repair. You do not want to travel to a desert in Peru and find out there that some components of your system do not work. • Weight restrictions for carry-on sensors apply. Your system manufacturer will advise you about these limitations. • Both the relative and the absolute flying heights may be limited (the former by regulations, the latter by lack of uplift and oxygen (in case of a model helicopter with gas engine). It is advisable to test your system under project conditions before you travel far. • Also, the operating distance is limited. It depends on radio link, energy support and visibility conditions.
• Fast data processing (download, on-line and real-time capabilities). Typically (although not always) UAV projects are covering only relatively small areas with small or medium format images. This allows efficient in-the-field data processing. Thus data validation and project corrections can be made while still on site. • Inexpensive platform. This applies to both the costs of a system and its operation. Due to the many different systems on the market there are also great differences in price (and performance). • High educational value. It is my experience that students love to work with such platforms. For the first time in their aerial photogrammetric career they can control the full process of project planning, flight execution, data processing, result representation, etc. by themselves. This generates a strong push of motivation.
Although, as mentioned before, the photogrammetric use of those platforms is by no means new, the current boom in applications is due to the fact that new sensors (digital cameras, GPS/INS) are used on the platforms and the flexibility and ease of raw data acquisition. While many systems where originally built just as “one-shot systems”, going up into the air for the acquisition of only a few images, without necessarily stereo overlap, we see today many more truly photogrammetric applications. These professional “photogrammetric” UAV systems can be characterized by: • Long flying time for image block data acquisition • Large image sequences (100 – several thousands) • Navigation devices for automated control of trajectory and orientation (autopilot), possibly supported by image-based navigation (new) • Stabilizing platform for precise image frame location • Image-based and/or range-based sensor(s), modular/exchangeable • Calibration of sensors and system • Accurate geo-referencing hard- and software (direct/indirect)
These advantages must be balanced against certain inherent problems of the technology, as there are: • Flight permissions are required. The regulations and legal conditions for UAV flights differ greatly from country to country and are also dependent on various factors like location of flight, flying height, size of platform, communication frequencies, etc. We had recently experienced a case where we had to get flight permissions from five different parties. Under such conditions very early project planning is absolutely necessary. Going out and just flying is by no means an advisable working mode, even if it would be possible technically. • Also, the safety issue is of great concern. After all, UAV technology is not in all cases very stable and absolutely reliable. There are certain rules which should be followed wisely: Do not lose the platform out of sight. Anything can happen once you lose eye contact. If autopilot is used and the platform runs in autonomous mode (which we recommend highly anyway) make sure you can switch to manual mode quickly – it may be necessary. • These platforms have no built-in intelligence. They cannot cope with unexpected situations (obstacles).
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Figure 5: Castle Landenberg, Obwalden, Switzerland, modelled from UAV images
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Figure 6: Quadrocopter over Drapham Dzong, Bhutan
Figure 8: Workflow of a photogrammetric UAV mission
• Automated image analysis and fast processing (batch and/or sequential estimation) • Standard photogrammetric pre-and post-processing functions • 3D modeling of objects and processes (geometry and texture) • Other suitable data processing software While this may be regarded as a wish-list, some of those functions are already available, others under development.
Figure 8 indicates the individual steps of data acquisition and processing and the associated degree of automation. “Semi-automation” can be understood either (a) as a fully automated process with substantial post-editing or (b) as an algorithm that has been designed from the very beginning as consisting of a combination of manual procedures and automated components, activated and controlled by a human operator. If “measurement of tie points” is said to be semi-automatic, it does not preclude cooperative cases where it works even fully automatically with success. The same applies to the measurement of control points. Under certain circumstances this can be done semi-automatically or even fully automatically. By far the most manual effort goes into the 3D modeling of complex objects. Here advancements in research are urgently required.
Applications Figure 1 shows the Copter1B with the autopilot system wePilot1000 of weControl AG, which was intensively used by my group in many projects, ranging from Archaeology/Cultural Heritage, Civil Engineering, Geology to Plant Sciences/Agriculture. Although it was originally not designed for photogrammetric use, it was later upgraded to photogrammetric functionality. This system has so far seen more than 40 project flights. Figure 2 shows a flight over a cornfield, where a Digital Surface Model had to be produced for studies and computations in Plant Sciences. In another application we have recorded an archaeological site in Peril Alto, Palpa, Peru (Archaic Period) for the German Archaeological Institute. We show two images from different flying heights - 325m (Figure 3) and 50m (Figure 4) above ground, which are used for different purposes. While the image of Figure 3 shows an overview of the area around the excavation site (indicating also the many looting holes in the ground), Figure 4 zooms into the excavation and can be used for the mapping and modeling of details. UAVs are suitable tools to record buildings, which are otherwise not easy to access. Figure 5 shows the 3D model of Castle Landenberg, Obwalden, Switzerland, which was modeled from UAV images. Even more, full ensembles and sites can be recorded. Figure 6 shows the flight of a quadrocopter over the archaeological site of Drapham Dzong, Bhutan and Figure 7 the resulting 3D model. The site is located at 3000m above sea level. We had to use a quadrocopter with electro-engine, since our model helicopter would not have worked at such altitude.
What will the future bring? We will see many more and also new applications of UAV technology. The integration of other sensors, besides panchromatic cameras, e.g. of infrared (near and far infrared), multi-spectral cameras and laserscanners is already on its way. This leads to new capabilities and applications. Manufacturers are working on the robustification of systems. Minification is also a topic of interest, although one should note that minification of components may result in a loss of quality. On the data processing side there is much room for useful R&D: • Integration of novel sensors (multiple cameras, LiDAR, etc.) • Development and testing of dynamic sensor models (LiDAR, Linear Array cameras) • System and sensor calibration of those new and possibly hybrid sensor configurations • Improvement of positioning and orientation accuracy • Integration of image-based navigation (e.g. by sequential estimation) • Improvement of the level of automation in 3D modeling • Emphasis on real-time and on-line processing The most urgent needs we see on the side of flight regulations. Here we need clear rules, laws and regulations, such that projects can be planned and executed in an orderly fashion. As evidenced by the developments in recent years, the many current activities and new applications UAVs have paved their way undoubtedly into the professional scenery of Geomatics. It is safe to say that we will even see an increase of activities in the years to come, making UAVs, both in terms of hardware and software development, a most interesting and challenging area for research, development and practice. This marks a clear transition from toys to tools.
Figure 7: 3D model of Drapham Dzong, Bhutan, reconstructed primarily from quadrocopter images
Prof. em. Dr. Armin Gruen, Institute of Conservation and Building Research, ETH Zuerich.
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