In visual Simultaneous Localization And Mapping (SLAM), detecting loop closures has been an important but difficult task. Currently, most solutions are based on the bag-of-words approach. Yet the possibility of deep neural network application to this task has not been fully explored due to the lack of appropriate architecture design and of sufficient training data. In this paper we demonstrate the applicability of deep neural networks by addressing both issues. Specifically we show that a feature pyramid Siamese neural network can achieve state-of-the-art performance on pairwise loop closure detection. The network is trained and tested on large-scale RGB-D datasets with a novel automatic loop closure labeling algorithm. Each image pair is labelled by how much the images overlap, allowing loop closure to be computed directly rather than by labor intensive manual labeling. We present an algorithm to adopt any large-scale generic RGB-D dataset for use in training deep loop-closure networks. We show for the first time that deep neural networks are capable of detecting loop closures, and we provide a method for generating large-scale datasets for use in evaluating and training loop closure detectors.
Currently, bag-of-words approach is the state-of-the-art method for loop closure detection @cite_37 @cite_28 @cite_3 @cite_17 in which each image is represented as a histogram of word-frequency of each word present in the dictionary generated offline from a large number of images. The computation of similarity is based on comparing the histograms @cite_2 between image pairs with certain heuristics such as spatial constraint or dynamic island @cite_38 . Image pairs with high similarity are deemed as possible loop closures.
@cite_38 @cite_37 @cite_28 @cite_3 @cite_2 @cite_17
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We present a method for detecting revisited places in a image sequence in real time by using efficient features. We introduce three important novelties to the bag-of-words plus geometrical checking approach. We use FAST keypoints and BRIEF descriptors, which are binary and very fast to compute (less that 20µs per point). To perform image comparisons, we make use of a bag of words that discretises the binary descriptor space and an inverse index. We also introduce the use of a direct index to take advantage of the bag of words to obtain correspondence points between two images efficiently, avoiding a matching of complexity Θ(n2). To detect loop closure candidates, we propose managing matches in groups to increase the reliability of the candidates returned by the bag of words. We present results in three real and public datasets, with 0.7–1.7 Km long trajectories. We obtain high precision and recall rates, spending 16 ms on average per image for the feature computation and the whole loop detection process in sequences with 19000 images, one order of magnitude less than other similar techniques. In state-of-the-art image retrieval systems, an image is represented by a bag of visual words obtained by quantizing high-dimensional local image descriptors, and scalable schemes inspired by text retrieval are then applied for large scale image indexing and retrieval. Bag-of-words representations, however: 1) reduce the discriminative power of image features due to feature quantization; and 2) ignore geometric relationships among visual words. Exploiting such geometric constraints, by estimating a 2D affine transformation between a query image and each candidate image, has been shown to greatly improve retrieval precision but at high computational cost. In this paper we present a novel scheme where image features are bundled into local groups. Each group of bundled features becomes much more discriminative than a single feature, and within each group simple and robust geometric constraints can be efficiently enforced. Experiments in Web image search, with a database of more than one million images, show that our scheme achieves a 49 improvement in average precision over the baseline bag-of-words approach. Retrieval performance is comparable to existing full geometric verification approaches while being much less computationally expensive. When combined with full geometric verification we achieve a 77 precision improvement over the baseline bag-of-words approach, and a 24 improvement over full geometric verification alone. The place recognition module is a fundamental component in SLAM systems, as incorrect loop closures may result in severe errors in trajectory estimation. In the case of appearance-based methods the bag-of-words approach is typically employed for recognizing locations. This paper introduces a novel algorithm for improving loop closures detection performance by adopting a set of visual words weights, learned offline accordingly to a discriminative criterion. The proposed weights learning approach, based on the large margin paradigm, can be used for generic similarity functions and relies on an efficient online leaning algorithm in the training phase. As the computed weights are usually very sparse, a gain in terms of computational cost at recognition time is also obtained. Our experiments, conducted on publicly available datasets, demonstrate that the discriminative weights lead to loop closures detection results that are more accurate than the traditional bag-of-words method and that our place recognition approach is competitive with state-of-the-art methods. In this paper a novel method for action recognition based on the bag of visual words approach is proposed. The main contribution is to model each action through a high level features vector computed as the histogram of the visual words: the visual words are extracted by analyzing global descriptors of the scene and their occurrences are evaluated according to a codebook, a kind of dictionary, which encodes the typical visual words, automatically extracted during the learning phase. The classification is performed by using an SVM classifier, trained only by using high level features vectors, in order to increase the overall reliability of the system. The experimentation has been conducted over two recently proposed datasets, the MIVIA and the MHAD, the promising results confirm the robustness and the stability of the proposed approach.