Obtaining a realistic and accurate model of the longitudinal dynamics is key for a good speed control of a self-driving car. It is also useful to simulate the longitudinal behavior of the vehicle with high fidelity. In this paper, a straightforward and generic method for obtaining the friction, braking and propulsion forces as a function of speed, throttle input and brake input is proposed. Experimental data is recorded during tests over the full speed range to estimate the forces, to which the corresponding curves are adjusted. A simple and direct balance of forces in the direction tangent to the ground is used to obtain an estimation of the real forces involved. Then a model composed of approximate spline curves that fit the results is proposed. Using splines to model the dynamic response has the advantage of being quick and accurate, avoiding the complexity of parameter identification and tuning of non-linear responses embedding the internal functionalities of the car, like ABS or regenerative brake. This methodology has been applied to LS2N's electric Renault Zoe but can be applied to any other electric car. As shown in the experimental section, a comparison between the estimated acceleration of the car using the model and the real one for a normal driving over a wide range of speeds along a trip of about 10 km/h reveals only 0.35 m/s2of error standard deviation in a range of ±2m/s2which is very encouraging.

In this paper, it is shown that the Enhanced Unified Camera Model, which is used to model fisheye cameras, projects straight lines into conic sections. Then a way to find equations of straight line projections is proposed. The method is applied to epipolar curves to adapt the Semi-Global Matching algorithm to fisheye stereo systems to compute a dense direct stereo correspondence without undistortion and rectification of fisheye images. It is done by efficient image sampling along an epipolar curve, using an algorithm for rasterization of implicit curves. A C++ implementation is available online.

Many ideas have been proposed to reduce traffic congestion. Driving a platoon of vehicles with constant spacing seems to be a promising idea as it increases traffic density. But keeping constant inter-vehicle spacing requires very reliable communication. Another control policy is to drive the platoon with a time headway between vehicles. It is a robust and well known policy but large inter-vehicle distances in addition to weak stability (unity error gain) near low frequencies make it less practical. We have proposed in [1], [2] a modification of the Constant Time Headway policy (CTH). This modification largely reduces the inter-vehicle distances using only one information shared between all vehicles. In this work, we propose an additional modification of our control law. This modification makes our control law similar, in form, to the classical constant spacing policy, but it requires to share only one information between the vehicles. This modification improves the stability of the platoon and removes the weak stability of the CTH near low frequencies. We prove the robustness of the control law in the presence of actuating lags, sensing and communication delays. This proof can also be used to prove the stability of the classical constant spacing policy in the presence of all previous delays, which makes our result more general than those established in the literature. Safety is also discussed and the maximum acceptable communication delay without losing safety is determined. Simulations have been done in many critical scenarios.

Finding solutions to traffic congestion is an active area of research. Many ideas have been proposed to reduce this problem, among of this ideas is moving in platoon. The constant time headway policy (CTH) is a very important platoon control policy, but it is too conservative and induces large inter-vehicle distances. Recently, we have proposed a modification of CTH [1], [2]. This modification reduces inter-vehicle distances and makes CTH very practical. This paper focuses on the control of platoons in urban areas. To control the vehicles, we assume that the longitudinal and the lateral dynamics are decoupled. We take into account a simplified engine model. We linearize the two dynamics using exact linearisation technique. Then, we use the modified CTH control law, adapted to urban platoons, for the longitudinal control and the robust sliding mode control for lateral control. The stability and the safety of the platoon are also studied. The conditions of stability of homogeneous and nonhomogeneous platoons are established. The conditions to verify the safety of the platoon for the longitudinal control (assuming stable and accurate lateral control) are exhibited. The weaknesses (large inter-vehicle distance, weak stability near low frequencies) of the CTH are solved. The improved performance and the safety of the platoon are verified by simulation using TORCS (The Open Racing Car Simulator). A platoon consisting of ten vehicles is created and tested on a curved track, keeping a small desired intervehicle distance. The stability and safety of the longitudinal and lateral controls are tested in many scenarios. These scenarios include platoon creation, changing the speed and emergency stop on straight and curved tracks. The results demonstrate the effectiveness of the proposed approach.

Optimizing inter-vehicle distances is very important to reduce traffic congestion on highways. A modification of the constant time headway policy (CTH) has been proposed in [1]. This modification significantly reduces inter-vehicle distances, but this reduction in the inter-distance may increase the risks of collisions. In this paper, the safety of the modified CTH applied to a homogeneous platoon is addressed. Many critical scenarios are discussed, including hard braking of the leader and followers in the event of communication loss. Safety conditions are presented. In addition, a method to find the maximum allowed delay to inform all the vehicles about communication loss, is also presented. Simulations have been run with 10 vehicles to check safety in the proposed scenarios.

Heavy traffic on highways requires the optimization of inter-distances between vehicles in order to reach time performance and to provide safety solution in transport. Variable spacing and constant spacing are the two policies for the longitudinal control of platoon. Variable spacing doesn't require a lot of data (position, speed...) from other vehicles, and string stability using only on-board information is obtained. However, inter-vehicle distances are very large, and hence traffic density is low. Constant spacing can offer string stability with high traffic density, but it requires at least data from the leader. In this paper, a novel expression of the variable spacing policy has been proposed. It is effective to decrease the distance between the cars, to become nearly equal to the constant spacing policy. It also enables increasing the string stability and the robustness of the control regarding to unmodeled lags, and it can avoid control torque saturation. This novel approach doesn't require heavy communication between the cars. The new control law has been evaluated by simulation with perfect system using Matlab, and with imperfect system using TORCS. The good results have demonstrated the effectiveness of the novel approach.

Deals with the determination of the full 3-D position and spatial orientation of a mobile robot from six azimuth and elevation angle measurements provided by an automatic theodolite. Stochastic approaches have already proved to be interesting for navigation algorithms, but they require a reliable initial estimation of the vehicle posture. Computing this initial posture without any a priori knowledge is not a straightforward mathematical exercise, especially if the landmarks are indistinguishable. In the paper, interval analysis is used to design a robust solution to this issue.

This paper presents a navigation system providing precise 3D position and spatial attitude data for slow outdoor vehicles. Our system uses an odometer and an automatic laser theodolite, the data of which are fused using a Kalman filter. We show through different experiments carried out with the evaluation station SESSYL that the high accuracies required for some civil-engineering tasks are fully satisfied, provided the beacons are properly positioned.

For precise localization of outdoor mobile robots, real-time kinematic Global Positioning System (RTK GPS) has obvious advantages: position data are given with centimeter-accuracy, and the required infrastructure is reduced to a sole fixed reference station. Yet, the use of this solution arises a number of issues, such as satellite maskings, or the existence of the so-called GPS latency, which delays the output of the localization data. This paper deals with the latter problem, and proposes a method to identify this parameter without using other external sensors. Experimental results carried out with the robot MELODY are presented so as to validate our solution.

In order to equip the compactors dedicated to road construction with an operator aiding system, a localization system using real-time kinematic GPS is considered. The paper presents the solutions we have developed to maintain an acceptable precision of the vehicle positioning even during the satellite masking phases. By combining a gyro with steering angle and speed measurements, we show that it is possible to obtain satisfying performances in dead reckoning navigation with low-cost equipment. A forward-backward Kalman filter is proposed to deal with particularly long maskings, which typically occur when the compactor works under bridges. Experimental results carried out in the framework of a cooperation with the Laboratoire Central des Fonts et Chaussees and the Centre d'Experimentations Routieres are presented to validate the proposed solutions.

In road layer compaction, it is essential that the right level of energy should be transmitted to the material, with a uniform distribution. This energy depends on the number of runs, or passes, of the machine. The main objective of CIRCOM is to assist the driver to perform the exact number of passes, at the right speed, everywhere on the surface to be compacted. From this improvement of quality in terms of level and uniformity of density, will result significant gains in road life-time, equipment operating time and material savings. To perform this task, it is essential to provide the operator and the system with an accurate and continuous location of the machine. The second objective is to record the actual work achieved by the compactor, in terms of trajectory and number of passes on every point, in order to feed the site database and to perform a global quality control at the site level. The main constraint is at the level of ergonomics; the system must be very simple and user-friendly.

A 2D mobile robot localization system which uses odometry and the azimuth angles of known landmarks is presented. Observability analysis helps to determine situations where such a system may undergo difficulties, and gives information on its behavior when one of the beacons is hidden. Experimental results are presented.

We present a localization system which computes, by extended Kalman filtering, the position and heading of a vehicle using both odometry and the measurement of the relative azimuth angles of known landmarks. Observability of the continuous system is studied and gives information on situations where the performance of the filter may deteriorate. Results of extensive real outdoor experiments with a wheel-type robot moving on a slightly uneven floor are reported. We show that the system achieves a precision of a few centimetres.