@article { ISI:000348881600008,
	title = {Visual contact with catadioptric cameras},
	journal = {ROBOTICS AND AUTONOMOUS SYSTEMS},
	volume = {64},
	year = {2015},
	month = {FEB},
	pages = {100-119},
	abstract = {Time to contact or time to collision (TTC) is utmost important information for animals as well as for mobile robots because it enables them to avoid obstacles; it is a convenient way to analyze the surrounding environment. The problem of TTC estimation is largely discussed in perspective images. Although a lot of works have shown the interest of omnidirectional camera for robotic applications such as localization, motion, monitoring, few works use omnidirectional images to compute the TTC. In this paper, we show that TTC can be also estimated on catadioptric images. We present two approaches for TTC estimation using directly or indirectly the optical flow based on de-rotation strategy. The first, called {\textquoteleft}{\textquoteleft}gradient based TTC{{\textquoteright}{\textquoteright}}, is simple, fast and it does not need an explicit estimation of the optical flow. Nevertheless, this method cannot provide a TTC on each pixel, valid only for para-catadioptric sensors and requires an initial segmentation of the obstacle. The second method, called {\textquoteleft}{\textquoteleft}TTC map estimation based on optical flow{{\textquoteright}{\textquoteright}}, estimates TTC on each point on the image and provides the depth map of the environment for any obstacle in any direction and is valid for all central catadioptric sensors. Some results and comparisons in synthetic and real images will be given. (C) 2014 Elsevier B.V. All rights reserved.},
	issn = {0921-8890},
	doi = {10.1016/j.robot.2014.09.036},
	author = {Benamar, F. and Elfkihi, S. and Demonceaux, C. and Mouaddib, E. and Aboutajdine, D.}
}
@conference { ISI:000351597600002,
	title = {GRADIENT-BASED TIME TO CONTACT ON PARACATADIOPTRIC CAMERA},
	booktitle = {2013 20TH IEEE INTERNATIONAL CONFERENCE ON IMAGE PROCESSING (ICIP 2013)},
	series = {IEEE International Conference on Image Processing ICIP},
	year = {2013},
	note = {20th IEEE International Conference on Image Processing (ICIP), Melbourne, AUSTRALIA, SEP 15-18, 2013},
	pages = {5-9},
	publisher = {Inst Elect \& Elect Engineers; IEEE Signal Proc Soc},
	organization = {Inst Elect \& Elect Engineers; IEEE Signal Proc Soc},
	abstract = {The problem of time to contact or time to collision (TTC) estimation is largely discussed in perspective images. However, a few works have dealt with images of catadioptric sensors despite of their utility in robotics applications. The objective of this paper is to develop a novel model for estimating TTC with catadioptric images relative to a planar surface, and to demonstrate that TTC can be estimated only with derivative brightness and image coordinates. This model, called {\textquoteleft}{\textquoteleft}gradient based time to contact{{\textquoteright}{\textquoteright}}, does not need high processing such as explicit estimation of optical flow and feature detection and/or tracking. The proposed method allows to estimate TTC and gives additional information about the orientation of planar surface. It was tested on simulated and real datasets.},
	isbn = {978-1-4799-2341-0},
	issn = {1522-4880},
	author = {Benamar, F. and El Fkihi, S. and Demonceaux, C. and Mouaddib, E. and Aboutajdine, D.}
}
@conference {Benamar20123602,
	title = {Time to contact estimation on paracatadioptric cameras},
	booktitle = {Proceedings - International Conference on Pattern Recognition},
	year = {2012},
	note = {cited By 2},
	pages = {3602-3605},
	url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84874558961\&partnerID=40\&md5=ed024edcf33e2e2b82c2adf2ecc505f3},
	author = {Benamar, F. and Demonceaux, C. and Fkihi, S.E. and Mouaddib, E. and Aboutajdine, D.}
}
