In this paper, we present a novel approach to accurately calibrate the kinematic model of a humanoid based on observations of its monocular camera. Our technique estimates the parameters of the complete model, consisting of the joint angle offsets of the whole body including the legs, as well as the camera extrinsic and intrinsic parameters. We cast the parameter estimation as a least-squares optimization problem. In the error function, we consider the residuals between camera observations of end-effector markers and their projections into the image based on the estimate of the calibration parameters. Furthermore, we developed an approach to automatically select a subset of configurations for the calibration process that yields a good trade-off between the number of observations and accuracy. As the experiments with a Nao humanoid show, we achieve an accurate calibration for this low-cost platform. Further, our approach to configuration selection yields substantially better optimization results compared to randomly chosen viable configurations. Hence, our system only requires a reduced number of configurations to achieve accurate results. Our optimization is general and the implementation, which is available online, can easily be applied to different humanoids.

In this paper, we present an integrated navigation system that allows humanoid robots to autonomously navigate in unknown, cluttered environments. From the data of an onboard consumer-grade depth camera, our system estimates the robot's pose to compensate for drift of odometry and maintains a heightmap representation of the environment. Based on this model, our system iteratively computes sequences of safe actions including footsteps and whole-body motions, leading the robot to target locations. Hereby, the planner chooses from a set of actions that consists of planar footsteps, step-over actions, as well as parameterized step-onto and step-down actions. To efficiently check for collisions during planning, we developed a new approach that takes into account the shape of the robot and the obstacles. As we demonstrate in experiments with a Nao humanoid, our system leads to robust navigation in cluttered environments and the robot is able to traverse highly challenging passages.

In this paper, we present an approach to traversability classification solely based on monocular images and odometry estimates. We iteratively estimate the ground plane by detecting and matching features. Since the features are only sparse in the images and do not lead to dense information about traversability, we present a technique to train appearance-based floor detectors. In this way, we achieve a dense classification of the image data. Our approach trains the classifiers online in a self-supervised fashion from the ground plane estimation. During robot navigation, the classifiers are automatically updated and applied to the image stream to decide which areas are traversable. From this information, the robot can compute a two-dimensional occupancy grid map of the environment and use it for planning collision-free paths. As we illustrate in thorough experiments with a real humanoid, the classification results of our approach are highly accurate and the resulting occupancy map enables the robot to reliably avoid obstacles during navigation. Our appearance-based classifiers can also be used to augment stereo or RGBD-data in close ranges where these sensors cannot provide any depth information.

In this paper, we present an approach to obstacle detection for collision-free, efficient humanoid robot navigation based on monocular images and sparse laser range data. To detect arbitrary obstacles in the surroundings of the robot, we analyze 3D data points obtained from a 2D laser range finder installed in the robot's head. Relying only on this laser data, however, can be problematic. While walking, the floor close to the robot's feet is not observable by the laser sensor, which inherently increases the risk of collisions, especially in nonstatic scenes. Furthermore, it is time-consuming to frequently stop walking and tilting the head to obtain reliable information about close obstacles. We therefore present a technique to train obstacle detectors for images obtained from a monocular camera also located in the robot's head. The training is done online based on sparse laser data in a self-supervised fashion. Our approach projects the obstacles identified from the laser data into the camera image and learns a classifier that considers color and texture information. While the robot is walking, it then applies the learned classifiers to the images to decide which areas are traversable. As we illustrate in experiments with a real humanoid, our approach enables the robot to reliably avoid obstacles during navigation. Furthermore, the results show that our technique leads to significantly more efficient navigation compared to extracting obstacles solely based on 3D laser range data acquired while the robot is standing at certain intervals.

Autonomous robot navigation in out-door scenarios gains increasing importance in various growing application areas. Whereas in non-urban domains such as deserts the problem of successful GPS-based navigation appears to be almost solved, navigation in urban domains particularly in the close vicinity of buildings is still a challenging problem. In such situations GPS accuracy significantly drops down due to multiple signal reflections with larger objects causing the so-called multipath error. In this paper we contribute a novel approach for incorporating multipath errors into the conventional GPS sensor model by analyzing environmental structures from online generated point clouds. The approach has been validated by experimental results conducted with an all-terrain robot operating in scenarios requiring close-to-building navigation. Presented results show that positioning accuracy can significantly be improved within urban domains.