In this paper, we propose a low-complexity histogram of oriented gradients (HOG) implementation for efficient video saliency framework. After showing how original HOG calculations present significant computation bottleneck for visual understanding pipes, we present the optimized HOG flow and algorithm for video saliency framework, which can reduce computational requirements without losing algorithmic performance. Furthermore, simplification for light-weight computations and data-reusable scanning for optimal memory usage are explained for improving system efficiency. Based on our testing and analysis, the proposed HOG implementation optimizes computational complexity and performance while maintaining the video saliency algorithm capability.

An urban operation of unmanned aerial vehicles (UAVs) demands a high level of autonomy for tasks presented in a cluttered environment. While fixed-wing UAVs have been well suited for long-endurance missions at a high altitude, their navigation inside an urban area brings more challenges in motion planning and control. The inability to hover and low agility in motion cause more difficulties on planning a feasible path in a compact region, and a limited payload allows only low-grade sensors for state estimation and control.

This paper presents a convenient self-calibration method for an inertial measurement unit (IMU) using matrix factorization. Using limited information about applied loads (accelerations or angular rates) available from natural references, the proposed method can linearly solve all the parameters of an IMU in any configuration of its inertial components. Our factorization-based calibration method exploits the bilinear form of an IMU measurement, which is the product of intrinsic calibration parameters and exerted loads. For a redundant IMU, we prove that partial knowledge of the loads, such as magnitude, can produce a linear solution space for a proper decomposition of the measurement. Theoretical analysis on this linear space reveals that a 1-D null space should be considered when load magnitudes are all equal (e.g., gravity loads). Degenerate load distributions are also geometrically identified to avoid singular measurement collection. Since a triad IMU has a lower number of sensor components than a 4-D parameter space, we propose an iterative factorization in which only initial bias is required. A wide convergence region of the bias can provide an automatic setting of the initial bias as the mean of the measurements. Performance of the proposed method is evaluated with respect to various noise levels and constraint types. Self-calibration capability is demonstrated using natural references, which are gravity for accelerometers and image stream from an attached camera for gyroscopes. Calibration results are globally optimal and identical to those of nonlinear optimization.

We present a drift-free attitude estimation method that uses image line segments for the correction of accumulated errors in integrated gyro rates when an unmanned aerial vehicle (UAV) operates in urban areas. Since man-made environments generally exhibit strong regularity in structure, a set of line segments that are either parallel or orthogonal to the gravitational direction can provide visual measurements for the absolute attitude from a calibrated camera. Line segments are robustly classified with the assumption that a single vertical vanishing point or multiple horizontal vanishing points exist. In the fusion with gyro angles, we introduce a new Kalman update step that directly uses line segments rather than vanishing points. The simulation and experiment based on urban images at distant views are provided to demonstrate that our method can serve as a robust visual attitude sensor for aerial robot navigation.

We propose a novel inertial-aided KLT feature tracking method robust to camera ego-motions. The conventional KLT uses images only and its working condition is inherently limited to small appearance change between images. When big optical flows are induced by a camera-ego motion, an inertial sensor attached to the camera can provide a good prediction to preserve the tracking performance. We use a low-grade MEMS-based gyroscope to refine an initial condition of the nonlinear optimization in the KLT. It increases the possibility for warping parameters to be in the convergence region of the KLT. For longer tracking with less drift, we use the affine photometric model and it can effectively deal with camera rolling and outdoor illumination change. Extra computational cost caused by this higher-order motion model is alleviated by restraining the Hessian update and GPU acceleration. Experimental results are provided for both indoor and outdoor scenes and GPU implementation issues are discussed.

We present an easy-to-use calibration method for MEMS inertial sensor units based on the Factorization method which was originally invented for shape-and-motion recovery in computer vision. Our method requires no explicit knowledge of individual motions applied during calibration procedure. Instead a set of motion constraints in the form of an inner-product is used to factorize sensor measurements into a calibration matrix (that represents intrinsic sensor parameters) and a motion matrix (that represents acceleration or angular velocity). These motion constraints can be collected quickly from a low-cost calibration apparatus. Our method is not limited to just triad configurations but also applicable to any coordination of more than three sensor elements. A redundant configuration has the benefit that all the calibration parameters including biases are estimated at once. Simulation and experiments are provided to verify the proposed method.

An imaging sensor made of multiple light-weight non-overlapping cameras is an effective sensor for a small unmanned aerial vehicle that has strong payload limitation. This paper presents a method for motion estimation by assuming that such a multi-camera system is a spherical imaging system (that is, the cameras share a single optical center). We derive analytically and empirically a condition for a multi-camera system to be modeled as a spherical camera. Interestingly, not only does the spherical assumption simplify the algorithms and calibration procedure, but also motion estimation based on that assumption becomes more accurate.

We present an efficient two-phase approach to motion planning for small fixed-wing unmanned aerial vehicles (UAVs) navigating in complex 3D air slalom environments. A coarse global motion planner first computes a kinematically feasible obstacle-free path in a discretized 3D workspace which roughly satisfies the kinematic constraints of the UAV. Given a coarse global path, a fine local motion planner is used to compute a more accurate trajectory for the UAV at a higher level of detail. The local planner is iterated as the vehicle traverses and refines the global path as needed up to its planning horizon. We also introduce a new planning heuristic for 3D motions of fixed-wing UAVs based on 2D Dubins curves, along with precomputed sets of motion primitives derived from the vehicle dynamics model in order to achieve high efficiency.

In this paper, we present a simple linear method for localization an indoor mobile robot based on a natural landmark model and a robust tracking algorithm. The landmark model is sets of three or more natural lines such as baselines, door edges and linear edges in tables or chairs, to take the advantages of fast landmark detection. Lucas-Kanade optical flow algorithm is applied to track the landmark model by using gradient descent. Then, a quick localization method for mobile robots from correspondent lines is proposed by adopting a linear technique. We present experimental results that demonstrate the robustness of the method with respect to image illumination and noises. The performance in indoor environments shows the feasibility of the proposed localization algorithm in real-time.

This paper presents a motion planning method for mobile manipulators for which the base locomotion is less precise than the manipulator control. In such a case, it is advisable to move the base to discrete poses from which the manipulator can be deployed to cover a prescribed trajectory. The proposed method finds base poses that not only cover the trajectory but also meet constraints on a measure of manipulability. We propose a variant of the conventional manipulability measure that is suited to the trajectory control of the end effector of the mobile manipulator along an arbitrary curve in three space. Results with implementation on a mobile manipulator are discussed.

Human friendly service robots such as home service robots, cleaning robots, entertainment robots take great attention in order to create new markets for robots since the markets for conventional industrial robots are saturating. It is a step to change the working environments of robots from industries to homes and offices, and to extend markets for robots from industrial markets to commercial home appliance markets. This paper introduces a home service robot 'ISSAC' applicable for vacuum cleaning, home security to find intruders and to transfer captured images of the intruder to the police or security companies, voice-based information service, real-time image transfer through wireless TCP/IP Ethernet and/or CDMA-2000 wireless communication, and a telepresence controllable by mobile computers such as pocket PC's and/or cellular phones. The overall controller is developed as a network-based layered modular controller using CAN (controller area network). The robot is tested in an apartment for a week successfully.

This paper deals with target tracking control of unicycle type mobile robots. Target tracking function is essential for autonomous robots such as guide robots, security guard robots, etc. In the field of mobile robot control, many control schemes for posture stabilization and trajectory tracking problem have been proposed. Target tracking control, however, cannot be achieved using these kinds of control laws. Therefore, a new global asymptotic stable controller for this problem is designed using the backstepping method. The stability of the system is proved using the Lyapunov function. Various simulation results validate the performance and theoretical analysis.