Appreciating a flower's texture, color, and shape leads to better drone landings

January 19, 2021

If you ever saw a honeybee hopping elegantly from flower to flower or avoiding you as you passed by, you may have wondered how such a tiny insect has such perfect navigation skills. These flying insects' skills are partially explained by the concept of optical flow: they perceive the speed with which objects move through their field of view. Robotics researchers have tried to mimic these strategies on flying robots, but with limited success. A team of TU Delft and the Westphalian University of Applied Sciences researchers therefore present an optical flow-based learning process that allows robots to estimate distances through the visual appearance (shape, color, texture) of the objects in view. This artificial intelligence (AI)-based learning strategy increases the navigation skills of small flying drones and entails a new hypothesis on insect intelligence. The article is published today in Nature Machine Intelligence.

How do honeybees land on flowers or avoid obstacles? One would expect such questions to be mostly of interest to biologists. However, the rise of small electronics and robotic systems has also made these questions relevant to robotics and Artificial Intelligence (AI). Small flying robots for example are extremely restricted in terms of the sensors and processing that they can carry onboard. If these robots are to be as autonomous as the much larger self-driving cars, they will have to use an extremely efficient type of artificial intelligence - similar to the highly developed intelligence possessed by flying insects.

Optical flow

One of the main tricks up the insect's sleeve is the extensive use of 'optical flow': the way in which objects move in their view. They use it to land on flowers and avoid obstacles or predators. Insects use surprisingly simple and elegant optical flow strategies to tackle complex tasks. For example, for landing honeybees use the optical flow "divergence", which captures how quickly things get bigger in view. If a honeybee were to fall to the ground, this divergence would keep increasing, with for example the grass becoming bigger in view ever faster. However, while landing honeybees employ a strategy of keeping the divergence constant by slowing down. The result is that they make smooth, soft landings.

"Our work on optical flow control started from enthusiasm about the elegant, simple strategies employed by flying insects" says Guido de Croon, professor of Bio-inspired Micro Air Vehicles and first author on the article. "However, developing the control methods to actually implement these strategies in flying robots turned out to be far from trivial. For example, our flying robots would not actually land, but they started to oscillate, continuously going up and down, just above the landing surface."

Fundamental limitations

Optical flow has two fundamental limitations that have been widely described in the growing literature on bio-inspired robotics. The first is that optical flow only provides mixed information on distances and velocities - and not on distance or velocity separately. To illustrate, if there are two landing drones and one of them flies twice as high and twice as fast as the other drone, then they experience exactly the same optical flow. However, for good control these two drones should actually react differently to deviations in the optical flow divergence. If a drone does not adapt its reactions to the height when landing, it will never arrive and start to oscillate above the landing surface. Second, for obstacle avoidance it is very unfortunate that in the direction in which a robot is moving, the optical flow is very small. This means that in that direction, optical flow measurements are noisy and hence provide very little information on the presence of obstacles. Hence, the most important obstacles - the ones that the robot is moving towards - are actually the hardest ones to detect!

Learning visual appearance as the solution

"We realized that both problems of optical flow would disappear if the robots were able to interpret not only optical flow, but also the visual appearance of objects in their environment", adds Guido de Croon. "This would allow robots to see distances to objects in the scene similarly to how we humans can estimate distances in a still picture. The only question was: How can a robot learn to see distances like that?"

The key to this question lay in a recent theory devised by De Croon, which showed that flying robots can actively induce optical flow oscillations to perceive distances to objects in the scene. In the approach proposed in the Nature Machine Intelligence article the robots use such oscillations in order to learn what the objects in their environment look like at different distances. In this way, the robot can for example learn how fine the texture of grass is when looking at it from different heights during landing, or how thick tree barks are at different distances when navigating in a forest.

Relevance to robotics and applications

"Learning to see distances by means of visual appearance led to much faster, smoother landings than we achieved before", says Christophe De Wagter, researcher at TU Delft and co-author of the article. "Moreover, for obstacle avoidance, the robots were now also able to see obstacles in the flight direction very clearly. This did not only improve obstacle detection performance, but also allowed our robots to speed up." The proposed methods will be very relevant to resource-constrained flying robots, especially when they operate in a rather confined environment, such as flying in greenhouses to monitor crop or keeping track of the stock in warehouses.

Relevance to biology

The findings are not only relevant to robotics, but also provide a new hypothesis for insect intelligence. "Typical honeybee experiments start with a learning phase, in which honeybees exhibit various oscillatory behaviors when they get acquainted with a new environment and related novel cues like artificial flowers", says Tobias Seidl, biologist and professor at the Westphalian University of Applied Sciences. "The final measurements presented in articles typically take place after this learning phase has finished and focus predominantly on the role of optical flow. The presented learning process forms a novel hypothesis on how flying insects improve their navigational skills, such as landing, over their lifetime. This suggests that we should set up more studies to investigate and report on this learning phase."
-end-


Delft University of Technology

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.