{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,2]],"date-time":"2026-06-02T09:30:51Z","timestamp":1780392651177,"version":"3.54.1"},"reference-count":24,"publisher":"MDPI AG","issue":"11","license":[{"start":{"date-parts":[[2019,6,2]],"date-time":"2019-06-02T00:00:00Z","timestamp":1559433600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003725","name":"National Research Foundation of Korea","doi-asserted-by":"publisher","award":["2017R1D1A1B03029992"],"award-info":[{"award-number":["2017R1D1A1B03029992"]}],"id":[{"id":"10.13039\/501100003725","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002613","name":"Ulsan National Institute of Science and Technology","doi-asserted-by":"publisher","award":["1.190011.01"],"award-info":[{"award-number":["1.190011.01"]}],"id":[{"id":"10.13039\/501100002613","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Civil Military Technology Cooperation Center","award":["2.180832.01"],"award-info":[{"award-number":["2.180832.01"]}]},{"DOI":"10.13039\/501100003052","name":"Ministry of Trade, Industry and Energy","doi-asserted-by":"publisher","award":["10062327"],"award-info":[{"award-number":["10062327"]}],"id":[{"id":"10.13039\/501100003052","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Due to payload restrictions for micro aerial vehicles (MAVs), vision-based approaches have been widely studied with their light weight characteristics and cost effectiveness. In particular, optical flow-based obstacle avoidance has proven to be one of the most efficient methods in terms of obstacle avoidance capabilities and computational load; however, existing approaches do not consider 3-D complex environments. In addition, most approaches are unable to deal with situations where there are wall-like frontal obstacles. Although some algorithms consider wall-like frontal obstacles, they cause a jitter or unnecessary motion. To address these limitations, this paper proposes a vision-based obstacle avoidance algorithm for MAVs using the optical flow in 3-D textured environments. The image obtained from a monocular camera is first split into two horizontal and vertical half planes. The desired heading direction and climb rate are then determined by comparing the sum of optical flows between half planes horizontally and vertically, respectively, for obstacle avoidance in 3-D environments. Besides, the proposed approach is capable of avoiding wall-like frontal obstacles by considering the divergence of the optical flow at the focus of expansion and navigating to the goal position using a sigmoid weighting function. The performance of the proposed algorithm was validated through numerical simulations and indoor flight experiments in various situations.<\/jats:p>","DOI":"10.3390\/s19112523","type":"journal-article","created":{"date-parts":[[2019,6,3]],"date-time":"2019-06-03T02:08:40Z","timestamp":1559527720000},"page":"2523","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":35,"title":["Vision-Based Obstacle Avoidance Strategies for MAVs Using Optical Flows in 3-D Textured Environments"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-9406-3624","authenticated-orcid":false,"given":"Gangik","family":"Cho","sequence":"first","affiliation":[{"name":"School of Mechanical, Aerospace and Nuclear Engineering, Ulsan National Institute of Science and Technology, 50, UNIST-gil, Banyeon-ri, Eonyang-eup, Ulju-gun, Ulsan 44919, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Jongyun","family":"Kim","sequence":"additional","affiliation":[{"name":"School of Mechanical, Aerospace and Nuclear Engineering, Ulsan National Institute of Science and Technology, 50, UNIST-gil, Banyeon-ri, Eonyang-eup, Ulju-gun, Ulsan 44919, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1051-9477","authenticated-orcid":false,"given":"Hyondong","family":"Oh","sequence":"additional","affiliation":[{"name":"School of Mechanical, Aerospace and Nuclear Engineering, Ulsan National Institute of Science and Technology, 50, UNIST-gil, Banyeon-ri, Eonyang-eup, Ulju-gun, Ulsan 44919, Korea"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2019,6,2]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Opromolla, R., Fasano, G., and Accardo, D. (2018, January 23\u201327). Perspectives and Sensing Concepts for Small UAS Sense and Avoid. Proceedings of the 2018 IEEE\/AIAA 37th Digital Avionics Systems Conference (DASC), London, UK.","DOI":"10.1109\/DASC.2018.8569338"},{"key":"ref_2","doi-asserted-by":"crossref","unstructured":"Mori, T., and Scherer, S. (2013, January 6\u201310). First results in detecting and avoiding frontal obstacles from a monocular camera for micro unmanned aerial vehicles. Proceedings of the 2013 IEEE International Conference on Robotics and Automation, Karlsruhe, Germany.","DOI":"10.1109\/ICRA.2013.6630807"},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Sun, D., Yang, X., Liu, M.Y., and Kautz, J. (2018, January 18\u201322). Pwc-net: Cnns for optical flow using pyramid, warping, and cost volume. Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, Salt Lake City, UT, USA.","DOI":"10.1109\/CVPR.2018.00931"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"13","DOI":"10.5772\/5715","article-title":"Optical Flow Based Robot Obstacle Avoidance","volume":"4","author":"Souhila","year":"2007","journal-title":"Int. J. Adv. Robot. Syst."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"195","DOI":"10.1016\/j.robot.2004.09.017","article-title":"A contribution to vision-based autonomous helicopter flight in urban environments","volume":"50","author":"Muratet","year":"2005","journal-title":"Robot. Auton. Syst."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Peng, X.Z., Lin, H.Y., and Dai, J.M. (2016, January 1\u20133). Path planning and obstacle avoidance for vision guided quadrotor UAV navigation. Proceedings of the 2016 12th IEEE International Conference on Control and Automation (ICCA), Kathmandu, Nepal.","DOI":"10.1109\/ICCA.2016.7505408"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"163","DOI":"10.1016\/j.ast.2017.05.012","article-title":"Inverse optical flow based guidance for UAV navigation through urban canyons","volume":"68","author":"Agrawal","year":"2017","journal-title":"Aerosp. Sci. Technol."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Liau, Y.S., Zhang, Q., Li, Y., and Ge, S.S. (2012, January 7\u201312). Non-metric navigation for mobile robot using optical flow. Proceedings of the 2012 IEEE\/RSJ International Conference on Intelligent Robots and Systems, Vilamoura, Algarve, Portugal.","DOI":"10.1109\/IROS.2012.6386221"},{"key":"ref_9","doi-asserted-by":"crossref","unstructured":"Gao, P., Zhang, D., Fang, Q., and Jin, S. (2017, January 28\u201330). Obstacle avoidance for micro quadrotor based on optical flow. Proceedings of the 2017 29th Chinese Control And Decision Conference (CCDC), Chongqing, China.","DOI":"10.1109\/CCDC.2017.7979206"},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Yang, Y.R., Gong, H.J., Wang, X.H., and Jia, S. (2016, January 12\u201314). Obstacle-avoidance strategy for small scale unmanned helicopter. Proceedings of the 2016 IEEE Chinese Guidance, Navigation and Control Conference (CGNCC), Nanjing, China.","DOI":"10.1109\/CGNCC.2016.7829028"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"894","DOI":"10.1016\/j.eswa.2011.07.087","article-title":"Autonomous quadrotor flight with vision-based obstacle avoidance in virtual environment","volume":"39","author":"Eresen","year":"2012","journal-title":"Expert Syst. Appl."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"252","DOI":"10.5139\/IJASS.2011.12.3.252","article-title":"Optical flow based collision avoidance of multi-rotor uavs in urban environments","volume":"12","author":"Yoo","year":"2011","journal-title":"Int. J. Aeronaut. Space Sci."},{"key":"ref_13","unstructured":"Muratet, L., Doncieux, S., and Meyer, J.A. (2004, January 23\u201326). A biomimetic reactive navigation system using the optical flow for a rotary-wing UAV in urban environment. Proceedings of the International Session on Robotics, Paris-Nord Villepinte, France."},{"key":"ref_14","first-page":"31","article-title":"Real Time Obstacle Avoidance and Navigation of a Quad-Rotor MAV Using Optical Flow Algorithms","volume":"12","author":"Prashanth","year":"2013","journal-title":"Sastech J."},{"key":"ref_15","unstructured":"Lucas, B.D., and Kanade, T. (1981, January 24\u201328). An iterative image registration technique with an application to stereo vision. Proceedings of the 7th International Joint Conference on Artificial Intelligence (IJCAI), Vancouver, BC, Canada."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"185","DOI":"10.1016\/0004-3702(81)90024-2","article-title":"Determining optical flow","volume":"17","author":"Horn","year":"1981","journal-title":"Artif. Intell."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Revaud, J., Weinzaepfel, P., Harchaoui, Z., and Schmid, C. (2015, January 7\u201312). Epicflow: Edge-preserving interpolation of correspondences for optical flow. Proceedings of the IEEE Conference on Computer Vision and Pattern Recognition, Boston, MA, USA.","DOI":"10.1109\/CVPR.2015.7298720"},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Dosovitskiy, A., Fischer, P., Ilg, E., Hausser, P., Hazirbas, C., Golkov, V., Van Der Smagt, P., Cremers, D., and Brox, T. (2015, January 7\u201313). Flownet: Learning optical flow with convolutional networks. Proceedings of the IEEE International Conference on Computer Vision, Santiago, Chile.","DOI":"10.1109\/ICCV.2015.316"},{"key":"ref_19","doi-asserted-by":"crossref","unstructured":"Weinzaepfel, P., Revaud, J., Harchaoui, Z., and Schmid, C. (2013, January 1\u20138). DeepFlow: Large displacement optical flow with deep matching. Proceedings of the IEEE International Conference on Computer Vision, Sydney, Australia.","DOI":"10.1109\/ICCV.2013.175"},{"key":"ref_20","unstructured":"Duchon, A.P., and Warren, W.H. (1994, January 2\u20135). Robot navigation from a Gibsonian viewpoint. Proceedings of the IEEE International Conference on Systems, Man and Cybernetics, San Antonio, TX, USA."},{"key":"ref_21","first-page":"224","article-title":"Maze navigation using optical flow","volume":"4","author":"Duchon","year":"1996","journal-title":"Anim. Animat."},{"key":"ref_22","doi-asserted-by":"crossref","unstructured":"Furrer, F., Burri, M., Achtelik, M., and Siegwart, R. (2016). Rotors\u2014A modular gazebo mav simulator framework. Robot Operating System (ROS), Springer.","DOI":"10.1007\/978-3-319-26054-9_23"},{"key":"ref_23","unstructured":"(2019, April 04). RotorS Simulator. Available online: http:\/\/github.com\/ethz-asl\/rotors_simulator."},{"key":"ref_24","unstructured":"(2019, April 04). Robot Operating System. Available online: http:\/\/www.ros.org."}],"container-title":["Sensors"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/11\/2523\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T12:55:35Z","timestamp":1760187335000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1424-8220\/19\/11\/2523"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2019,6,2]]},"references-count":24,"journal-issue":{"issue":"11","published-online":{"date-parts":[[2019,6]]}},"alternative-id":["s19112523"],"URL":"https:\/\/doi.org\/10.3390\/s19112523","relation":{},"ISSN":["1424-8220"],"issn-type":[{"value":"1424-8220","type":"electronic"}],"subject":[],"published":{"date-parts":[[2019,6,2]]}}}