The Revisiting Problem in Simultaneous Localization and Mapping: A Survey on Visual Loop Closure Detection

Where am I? This is one of the most critical questions that any intelligent system should answer to decide whether it navigates to a previously visited area. This problem has long been acknowledged for its challenging nature in simultaneous localization and mapping (SLAM), wherein the robot needs to correctly associate the incoming sensory data to the database allowing consistent map generation. The significant advances in computer vision achieved over the last 20 years, the increased computational power, and the growing demand for long-term exploration contributed to efficiently performing such a complex task with inexpensive perception sensors. In this article, visual loop closure detection, which formulates a solution based solely on appearance input data, is surveyed. We start by briefly introducing place recognition and SLAM concepts in robotics. Then, we describe a loop closure detection system's structure, covering an extensive collection of topics, including the feature extraction, the environment representation, the decision-making step, and the evaluation process. We conclude by discussing open and new research challenges, particularly concerning the robustness in dynamic environments, the computational complexity, and scalability in long-term operations. The article aims to serve as a tutorial and a position paper for newcomers to visual loop closure detection.Comment: 25 pages, 15 figure

VNI-Net: Vector Neurons-based Rotation-Invariant Descriptor for LiDAR Place Recognition

LiDAR-based place recognition plays a crucial role in Simultaneous Localization and Mapping (SLAM) and LiDAR localization. Despite the emergence of various deep learning-based and hand-crafting-based methods, rotation-induced place recognition failure remains a critical challenge. Existing studies address this limitation through specific training strategies or network structures. However, the former does not produce satisfactory results, while the latter focuses mainly on the reduced problem of SO(2) rotation invariance. Methods targeting SO(3) rotation invariance suffer from limitations in discrimination capability. In this paper, we propose a new method that employs Vector Neurons Network (VNN) to achieve SO(3) rotation invariance. We first extract rotation-equivariant features from neighboring points and map low-dimensional features to a high-dimensional space through VNN. Afterwards, we calculate the Euclidean and Cosine distance in the rotation-equivariant feature space as rotation-invariant feature descriptors. Finally, we aggregate the features using GeM pooling to obtain global descriptors. To address the significant information loss when formulating rotation-invariant descriptors, we propose computing distances between features at different layers within the Euclidean space neighborhood. This greatly improves the discriminability of the point cloud descriptors while ensuring computational efficiency. Experimental results on public datasets show that our approach significantly outperforms other baseline methods implementing rotation invariance, while achieving comparable results with current state-of-the-art place recognition methods that do not consider rotation issues

Semantic Segmentation in Long-term Visual Localization

Tato práce má pět hlavních cílů. Nejprve mapuje datové sady používané pro dlouhodobou vizuální lokalizaci a vybere vhodné datové sady pro další vyhodnocení. Dále je vybrán a vylepšen jeden ze současných state-of-the-art přístupů. Výsledky s pečlivě vyladěnými parametry vybrané metody dosahují lepších výsledků lokalizace. Dále je ukázáno, že dynamické objekty v obrázku jsou pro dlouhodobou vizuální lokalizaci zbytečné, protože neobsahují žádnou užitečnou informaci a lze je zcela odstranit. Čtvrtým cílem této práce je pokusit se vložit sémantickou informaci do detektoru a deskriptoru klíčových bodů SuperPoint úpravou trénovacích dat. Závěrem je dosaženo nových state-of-the-art výsledků na vybrané datové sadě aplikací nového přístupu filtrování klíčových bodů založeného na sémantické informaci. Význam této práce ukazuje důležitost analýzy obrazové informace v úloze dlouhodobé vizuální lokalizace a detekce klíčových bodů obecně.ObhájenoThis thesis has five main goals. At first, it maps the datasets used for long-term visual localization and selects viable datasets for further evaluation. Next, one of the current state-of-the-art pipelines is selected and enhanced. Results with carefully fine-tuned methods' parameters accomplish better localization results. Furthermore, it shows that dynamic objects in an image are unnecessary for long-term visual localization because they do not contain any helpful information and can be ignored. The fourth goal in this thesis is to embed semantic segmentation information into the SuperPoint keypoint detector and descriptor by editing training data. Finally, the new state-of-the-art results on a selected dataset are achieved by applying a novel keypoint filtering approach based on semantic segmentation information. The significance of this work shows the importance of analyzing underlying image information in long-term visual localization and keypoint detection in general

The ecological thought of Thomas Hardy: a comparative study of his selected novels and their movie adaptations

‘The Ecological Thought of Thomas Hardy: A Comparative Study of his Selected Novels and their Movie Adaptations’ is an inter-textual analysis of Hardy’s novels and their movie adaptations from an ecocritical perspective. My study explores the ways in which verbal and audio-visual narratives engage with human and non-human relationships, and thus offer alternative perceptions of nature in a historical era marked by an escalating ecological crisis and environmental anxiety. I examine the possibility of human and non-human co-existence as well as various modes of human and non-human entanglement and connection: labour-related, material, acoustic, semiotic, corporeal, as well as emotive. This study is interdisciplinary in nature, drawing on an eclectic mix of theories, mainly ecocriticism, eco-cinema and adaptation studies. The conceptual framework developed here identifies convergent and divergent ecocritical strands of thought between the novels and their movie adaptations. My project recognizes the complexity of both the verbal and the audio-visual narratives, illuminating complex eco-centric and occasionally anthropocentric visions across the fiction as well as the movies. While highlighting similarities and dissimilarities between novels and their movie adaptations, my project recognizes the originality and autonomy of movie adaptations as well as the artistic creativity of their respective directors. Hence, my research contributes and expands ecocritical studies of Hardy’s narrative prose fiction as well as the existing scholarship on adaptations of his works. By analyzing adaptations in ecocritical terms, my project extends debates about eco-cinema, seeking the possibility to push beyond a study of environmental documentaries and wildlife films. With this aim in my mind, I hope to encourage a better, more nuanced engagement with the natural and the non-human in the related field of the film industry, especially representations of the natural world in adaptations

Engagements with the pastoral mode in the poetry and plays of Derek Walcott

The intention of this thesis is to investigate engagements with the pastoral mode in the poetry and plays of Derek Walcott. This will be achieved through a focus upon four key areas: Edenic symbolism, classical reception, allusions to the visual arts, and pastoral drama. The pastoral is a complex mode, with a long literary history. I argue that Walcott engages with the mode in a process of transformative interactions with the legacy of Eurocentric representations of Caribbean settings, the notion of the Caribbean as an Edenic space, the classical tradition including the pastorals of Theocritus and Virgil, the tradition of landscape art and both the piscatory pastoral and pastoral drama. These engagements allow for the subversion of generic expectations, and a revisionary, transformative approach to the pastoral mode and its many associations. This results in a distinctly Walcottian type of pastoral, one which evades reductive idealisation and restrictive uses of aesthetic models, in favour of a creative and profound engagement with pastoral’s core themes

Ithacas, a photographic journey:exile and displacement arising from the Greek crisis

The economic crisis in Greece, that became an acute reality in 2010, revealed the preexisting cultural crisis in the country and created the need to redefine the Greek identity. This practice-based research explores this particular need through the conditions of immigration to European metropolises, repatriation from abroad and internal migration to Greek islands that are incited by the crisis, and are part of the many consequences of the crisis. The aim is to create a photographic narrative on the subject with an approach embedded within it that emphasises the need to recreate both Greek identity and Greek photography, as the latter was never incorporated into a Greek cultural context but rather developed as an imitation of European and North-American photographic trends. The project draws upon original visual and academic research to construct a photographic narrative. The process of image making works as a methodological tool that uses morphological, aesthetic, and narrative elements from the genres of subjective documentary and landscape photography and develops in parallel with the theoretical research on the areas of (i) displacement and exile, (ii) Greek culture and aesthetics and (iii) Greek landscape photography. To achieve a photographic approach that can be described as Greek, three basic methods are used; (i) the reappropriation of the myth of Odysseus as a representational and symbolic structure of the voyage of contemporary Greek migrants towards their own Ithacas, (ii) the appliance of the Neohellenic principle of entopia in image making as a code of symbolism, and (iii) the use of symbolic Greek landscape images to re-create/restore a collective memory. The project uses the mythological ten-year journey on the sea of Odysseus towards his home and redirects it to represent the migratory flows of Greek neo-migrants. The story is seen from the perspective of Odysseus, who becomes the narrator that experiences displacement and tries to define his/her identity in relation to the borders of each place he/she resides. The narrative, that is presented as four books in a slipcase, consists of two main types of images, colour landscapes and black-and-white instant images. The first explore the concept of the border and build the inner landscape of the narrator, based on theoretical research on displacement and exile and the code of symbolism inspired by Neohellenism. The latter refer to archive images and use representations of the Greek landscape to explore cultural memory. In this thesis, the final outcome is analysed in a Greek cultural context and it is argued that just as the redefinition of Greek identity is possible by redefining the traditional values of Greek culture, the search for the new Greek photographic identity can be achieved by studying the principles of Greek culture and applying them info photography