A map generated by a SLAM Robot. SLAM algorithms are tailored to the available resources, hence not aimed at perfection, but at operational compliance
A map generated by a SLAM Robot. SLAM algorithms are tailored to the available resources, hence not aimed at perfection, but at operational compliance. They provide an estimation of the posterior probability function for robotics for dummies pdf pose of the robot and for the parameters of the map. They provide a set which encloses the pose of the robot and a set approximation of the map.
New SLAM algorithms remain an active research area, and are often driven by differing requirements and assumptions about the types of maps, sensors and models as detailed below. Many SLAM systems can be viewed as combinations of choices from each of these aspects. Topological SLAM approaches have been used to enforce global consistency in metric SLAM algorithms. Typically the cells are assumed to be statistically independent in order to simplify computation. This can include map annotations to the level of marking locations of individual white line segments and curbs on the road. SLAM will always use several different types of sensors, and the powers and limits of various sensor types have been a major driver of new algorithms.
Statistical independence is the mandatory requirement to cope with metric bias and with noise in measures. Different types of sensors give rise to different SLAM algorithms whose assumptions are which are most appropriate to the sensors. Most practical SLAM tasks fall somewhere between these visual and tactile extremes. Sensor models divide broadly into landmark-based and raw-data approaches. Landmarks are uniquely identifiable objects in the world whose location can be estimated by a sensor—such as wifi access points or radio beacons. Visual and LIDAR sensors are informative enough to allow for landmark extraction in many cases. SLAM as a tribute to erratic wireless measures.
From a SLAM perspective, these may be viewed as location sensors whose likelihoods are so sharp that they completely dominate the inference. However GPS sensors may go down entirely or in performance on occasions, especially during times of military conflict which are of particular interest to some robotics applications. As a part of the model, the kinematics of the robot is included, to improve estimates of sensing under conditions of inherent and ambient noise. The dynamic model balances the contributions from various sensors, various partial error models and finally comprises in a sharp virtual depiction as a map with the location and heading of the robot as some cloud of probability.
Mapping is the final depicting of such model, the map is either such depiction or the abstract term for the model. For 2D robots, the kinematics are usually given by a mixture of rotation and “move forward” commands, which are implemented with additional motor noise. Unfortunately the distribution formed by independent noise in angular and linear directions is non-Gaussian, but is often approximated by a Gaussian. An alternative approach is to ignore the kinematic term and read odometry data from robot wheels after each command—such data may then be treated as one of the sensors rather than as kinematics. Bayesian filtering with random finite sets that provide superior performance to leading feature-based SLAM algorithms in challenging measurement scenarios with high false alarm rates and high missed detection rates without the need for data association.
Non-static environments, such as those containing other vehicles or pedestrians, continue to present research challenges. SLAM with DATMO is a model which tracks moving objects in a similar way to the agent itself. Loop closure is the problem of recognizing a previously-visited location and updating beliefs accordingly. This can be a problem because model or algorithm errors can assign low priors to the location.
Typical loop closure methods apply a second algorithm to compute some type of sensor measure similarity, and re-set the location priors when a match is detected. Active SLAM” studies the combined problem of SLAM with deciding where to move next in order to build the map as efficiently as possible. The need for active exploration is especially pronounced in sparse sensing regimes such as tactile SLAM. Multi agent SLAM” extends this problem to the case of multiple robots coordinating themselves to explore optimally. SLAM systems such as RatSLAM.