Place recognition and loop-closure detection are main challenges in the localization, mapping and navigation tasks of self-driving vehicles. In this paper, we solve the loop-closure detection problem by incorporating the deep-learning based point cloud description method and the coarse-to-fine sequence matching strategy. More specifically, we propose a deep neural network to extract a global descriptor from the original large-scale 3D point cloud, then based on which, a typical place analysis approach is presented to investigate the feature space distribution of the global descriptors and select several super keyframes. Finally, a coarse-to-fine strategy, which includes a super keyframe based coarse matching stage and a local sequence matching stage, is presented to ensure the loop-closure detection accuracy and real-time performance simultaneously. Thanks to the sequence matching operation, the proposed approach obtains an improvement against the existing deep-learning based methods. Experiment results on a self-driving vehicle validate the effectiveness of the proposed loop-closure detection algorithm.
Handcrafted local features, such as Shape context @cite_21 and SHOT @cite_9 , first find a keypoint, divide neighboring points into different bins, and encode a histogram with the defined pattern of neighboring bins. Moreover, FPHF @cite_5 , present for 2.5D scans, which is a point-wise histogram based 3D feature descriptor. Global descriptors of the local point cloud were also presented. M2DP was proposed in @cite_13 , which projects the original point cloud to several planes and extracts a global representation. ESF @cite_8 implemented the concatenation of histograms generated from shape functions. Local features usually require normal vectors of keypoints and thus are not suitable for large-scale place recognition tasks in outdoor scenarios. Global descriptors are usually tailored to specific tasks and therefore have poor generalization features.
@cite_8 @cite_9 @cite_21 @cite_5 @cite_13
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This work addresses the problem of real-time 3D shape based object class recognition, its scaling to many categories and the reliable perception of categories. A novel shape descriptor for partial point clouds based on shape functions is presented, capable of training on synthetic data and classifying objects from a depth sensor in a single partial view in a fast and robust manner. The classification task is stated as a 3D retrieval task finding the nearest neighbors from synthetically generated views of CAD-models to the sensed point cloud with a Kinect-style depth sensor. The presented shape descriptor shows that the combination of angle, point-distance and area shape functions gives a significant boost in recognition rate against the baseline descriptor and outperforms the state-of-the-art descriptors in our experimental evaluation on a publicly available dataset of real-world objects in table scene contexts with up to 200 categories. AbstractThis paper presents alocal3D descriptor forsurface matching dubbed SHOT.Our proposal stems from a taxonomy of existing methods which highlightstwo major approaches, referred to as Signatures and Histograms, inher-ently emphasizing descriptiveness and robustness respectively. We formulatea comprehensive proposal which encompasses a repeatable local referenceframe as well as a 3D descriptor, the latter featuring an hybrid structurebetween Signatures and Histograms so as to aim at a more favorable bal-ance between descriptive power and robustness. A quite peculiar trait of ourmethod concerns seamless integration of multiple cues within the descrip-tor to improve distinctiveness, which is particularly relevant nowadays dueto the increasing availability of aﬀordable RGB-D sensors which can gatherboth depth and color information. A thorough experimental evaluation basedon datasets acquired with diﬀerent types of sensors, including a novel RGB-D dataset, vouches that SHOT outperforms state-of-the-art local descriptorsin experiments addressing descriptor matching for object recognition, 3Dreconstruction and shape retrieval.Keywords: Surface Matching, 3D Descriptors, Object Recognition, 3DReconstruction1. IntroductionAutomatic recognition of shapes in 3D data, also referred to as surfacematching, attracts growing interest in the research community, with appli-cation to areas such as shape retrieval, 3D reconstruction, object recogni-tion categorization, manipulation and grasping, robot localization and nav-igation. A key enabling factor for the development of this technology is We present a novel approach to measuring similarity between shapes and exploit it for object recognition. In our framework, the measurement of similarity is preceded by: (1) solving for correspondences between points on the two shapes; (2) using the correspondences to estimate an aligning transform. In order to solve the correspondence problem, we attach a descriptor, the shape context, to each point. The shape context at a reference point captures the distribution of the remaining points relative to it, thus offering a globally discriminative characterization. Corresponding points on two similar shapes will have similar shape contexts, enabling us to solve for correspondences as an optimal assignment problem. Given the point correspondences, we estimate the transformation that best aligns the two shapes; regularized thin-plate splines provide a flexible class of transformation maps for this purpose. The dissimilarity between the two shapes is computed as a sum of matching errors between corresponding points, together with a term measuring the magnitude of the aligning transform. We treat recognition in a nearest-neighbor classification framework as the problem of finding the stored prototype shape that is maximally similar to that in the image. Results are presented for silhouettes, trademarks, handwritten digits, and the COIL data set. In our recent work [1], [2], we proposed Point Feature Histograms (PFH) as robust multi-dimensional features which describe the local geometry around a point p for 3D point cloud datasets. In this paper, we modify their mathematical expressions and perform a rigorous analysis on their robustness and complexity for the problem of 3D registration for overlapping point cloud views. More concretely, we present several optimizations that reduce their computation times drastically by either caching previously computed values or by revising their theoretical formulations. The latter results in a new type of local features, called Fast Point Feature Histograms (FPFH), which retain most of the discriminative power of the PFH. Moreover, we propose an algorithm for the online computation of FPFH features for realtime applications. To validate our results we demonstrate their efficiency for 3D registration and propose a new sample consensus based method for bringing two datasets into the convergence basin of a local non-linear optimizer: SAC-IA (SAmple Consensus Initial Alignment). In this paper, we present a novel global descriptor M2DP for 3D point clouds, and apply it to the problem of loop closure detection. In M2DP, we project a 3D point cloud to multiple 2D planes and generate a density signature for points for each of the planes. We then use the left and right singular vectors of these signatures as the descriptor of the 3D point cloud. Our experimental results show that the proposed algorithm outperforms state-of-the-art global 3D descriptors in both accuracy and efficiency.