Recent advancements in self-supervised learning in the point cloud domain have demonstrated significant potential. However, these methods often suffer from drawbacks such as lengthy pre-training time, the necessity of reconstruction in the input space, and the necessity of additional modalities. In order to address these issues, we introduce Point-JEPA, a joint embedding predictive architecture designed specifically for point cloud data. To this end, we introduce a sequencer that orders point cloud patch embeddings to efficiently compute and utilize their proximity based on their indices during target and context selection. The sequencer also allows shared computations of the patch embeddings' proximity between context and target selection, further improving the efficiency. Experimentally, our method demonstrates state-of-the-art performance while avoiding the re-construction in the input space or additional modality. In particular, Point-JEPA attains a classification accuracy of 93.7 ±0.2 % for linear SVM on ModelNet40 surpassing all other self-supervised models. Moreover, Point-JEPA also establishes new state-of-the-art performance levels across all four few-shot learning evaluation frameworks. The code is available at https://github.com/Ayumu-J-S/Point-JEPA

Individual tree segmentation from terrestrial laser scanning (TLS) point clouds is essential for precise forest inventory, instance-level tree modeling, and the estimation of forest stock volume. However, current instance-level segmentation techniques encounter significant challenges in complex forest environments, particularly those characterized by dense understory vegetation and substantial crown overlap in natural forests. These complexities reduce segmentation accuracy and limit the generalizability of existing methods across diverse forest types. This paper presents a unified method for individual tree segmentation that integrates trunk localization with crown segmentation. The trunk localization uses normal vector features to eliminate non-trunk slice points, employs an enhanced DBSCAN algorithm for trunk slice separation, and refines trunk positions by fitting circular-like trunk slices using the Hough transform. This integrated approach ensures precise segmentation and optimization of final trunk positions. Subsequently, a graph-based optimization method is applied for crown segmentation. This method incorporates supervoxel technology, an optimal Euclidean distance metric between supervoxels, and a supervoxel similarity metric to construct an optimal undirected graph. Tree crown supervoxels are segmented by tracing the shortest path from the crown supervoxels to their corresponding tree roots. We validated the proposed method on eight sample plots representing various complexities and forest types. For tree trunk localization, the proposed method achieved an average Mean accuracy of 0.761, which is 27% higher than the best result among the three traditional methods. For crown segmentation, it achieved an average mIoU of 0.645, marking a 31% improvement over the best baseline performance. The source code for our individual tree segmentation method is available at https://github.com/TLS-tree/tree-segmentation.

3D models of urban buildings have paramount importance to most digital urban applications. However, requirement of large storage and high computational cost for processing the geometric details of urban objects have been observed as a major limitation to existing 3D modeling approaches. This draws the need of lightweight modeling techniques requiring less computational storage to capture the details of the urban entities. Additionally these models should facilitate accelerated visualizations along with consuming lesser bandwidth for online applications. In this paper, we propose a lightweight urban modeling method using gradient structure tensors based feature point extraction to produce highly detailed lightweight 3D building models from LiDAR scans. Further, a mean cost-based edge collapse operation is proposed to preserve the feature points. The qualitative and quantitative analysis and comparative study of different building façade models shows the efficacy of our method in generating simplified models with a trade-off between model simplification and accuracy.

Graph Neural Networks have brought many breakthroughs in graph representation learning and boosted the state of the art in many data processing domains including point cloud learning. Graph structures provide the relative neighborhood information to unordered point clouds and help the exploration of topological structures for the understanding of complex scenes. Therefore, in this paper, we propose novel neural network architectures leveraging graph attention for point cloud-based classification and segmentation. The proposed architectures construct a connected graph from point cloud scans and employ a global aware attention module using global, local, and self-feature information for point cloud segmentation and classification. Various experiments on different datasets (ModelNet40 [1], ShapeNet [2], S3DIC [3], and Semantic3D [4]) show that our methods yield comparable results for classification, part segmentation, and semantic segmentation.

In this work, we present an attention based feature aggregation technique in graph neural networks (GNN) for detecting objects in LiDAR scan. We first employ a distance-aware downsampling scheme that not only enhances the algorithmic performance but also retains maximum geometric features of objects even if they lie far from the sensor. Our graph attention formulation uses novel neighborhood aggregation strategies through per node masked attention by combining local and self features. The experiments on KITTI dataset show that the proposed method yields comparable results for 3D object detection under GNN models category.

Abstract Curve reconstruction from unstructured points in a plane is a fundamental problem with many applications that has generated research interest for decades. Involved aspects like handling open, sharp, multiple and non‐manifold outlines, run‐time and provability as well as potential extension to 3D for surface reconstruction have led to many different algorithms. We survey the literature on 2D curve reconstruction and then present an open‐sourced benchmark for the experimental study. Our unprecedented evaluation of a selected set of planar curve reconstruction algorithms aims to give an overview of both quantitative analysis and qualitative aspects for helping users to select the right algorithm for specific problems in the field. Our benchmark framework is available online to permit reproducing the results and easy integration of new algorithms.

Procedural noise functions are fundamental tools in computer graphics used for synthesizing virtual geometry and texture patterns. Ideally, a procedural noise function should be compact, aperiodic, parameterized, and randomly accessible. Traditional lattice noise functions such as Perlin noise, however, exhibit periodicity due to the axial correlation induced while hashing the lattice vertices to the gradients. In this paper, we introduce a parameterized lattice noise called prime gradient noise (PGN) that minimizes discernible periodicity in the noise while enhancing the algorithmic efficiency. PGN utilizes prime gradients, a set of random unit vectors constructed from subsets of prime numbers plotted in polar coordinate system. To map axial indices of lattice vertices to prime gradients, PGN employs Szudzik pairing, a bijection F : ℕ 2 → ℕ. Compositions of Szudzik pairing functions are used in higher dimensions. At the core of PGN is the ability to parameterize noise generation though prime sequence offsetting which facilitates the creation of fractal noise with varying levels of heterogeneity ranging from homogeneous to hybrid multifractals. A comparative spectral analysis of the proposed noise with other noises including lattice noises show that PGN significantly reduces axial correlation and hence, periodicity in the noise texture. We demonstrate the utility of the proposed noise function with several examples in procedural modeling, parameterized pattern synthesis, and solid texturing.

Metro subway systems with underground tunnels form the backbone of urban transportations and therefore, accurate monitoring and maintenance of such subway systems are extremely necessary for a hassle-free daily commutation of billions of people. Though 3-D models of tunnels are widely used for the deformation monitoring of such subway tunnels, existing model-based tunnel monitoring systems rely on coarse geometric models and hence fail to capture complete tunnel health information. We present a two-stage algorithm to create high-fidelity geometric models of tunnel lining from Terrestrial Laser Scanning (TLS) point clouds. Tunnel geometry, defined at the detailed block entity level, is constructed through a data-driven block segmentation algorithm and a model-driven assembly technique. In our approach, the 3-D tunnel block segmentation problem has been translated into a bolt and lining joint recognition problem from 2-D images unfolded from the 3-D scans. The segmented 3-D blocks are matched with a set of predefined 3-D templates from a primitive library via a constraint total least squares matching method and the matched 3-D templates are assembled to create the final watertight tunnel model. The proposed tunnel modeling method has been comprehensively evaluated on Changzhou, Nanjing, and Wuhan tunnel data sets in terms of outliers, missing data, point density, topological representation, robustness, and geometric accuracy. The experiments on Nanjing and Changzhou metro tunnels show that the geometric model fitting incurs an error of only 7 mm, which is almost consistent with a mean density of 6 mm of these two data sets. Experimental results validate the advantages and potentials of the proposed tunnel modeling method.

Abstract We present an incremental Voronoi vertex labelling algorithm for approximating contours, medial axes and dominant points (high curvature points) from 2D point sets. Though there exist many number of algorithms for reconstructing curves, medial axes or dominant points, a unified framework capable of approximating all the three in one place from points is missing in the literature. Our algorithm estimates the normals at each sample point through poles (farthest Voronoi vertices of a sample point) and uses the estimated normals and the corresponding tangents to determine the spatial locations (inner or outer) of the Voronoi vertices with respect to the original curve. The vertex classification helps to construct a piece‐wise linear approximation to the object boundary. We provide a theoretical analysis of the algorithm for points non‐uniformly (ε‐sampling) sampled from simple, closed, concave and smooth curves. The proposed framework has been thoroughly evaluated for its usefulness using various test data. Results indicate that even sparsely and non‐uniformly sampled curves with outliers or collection of curves are faithfully reconstructed by the proposed algorithm.

Abstract The medial axis transform has applications in numerous fields including visualization, computer graphics, and computer vision. Unfortunately, traditional medial axis transformations are usually brittle in the presence of outliers, perturbations and/or noise along the boundary of objects. To overcome this limitation, we introduce a new formulation of the medial axis transform which is naturally robust in the presence of these artefacts. Unlike previous work which has approached the medial axis from a computational geometry angle, we consider it from a numerical optimization perspective. In this work, we follow the definition of the medial axis transform as ‘the set of maximally inscribed spheres’. We show how this definition can be formulated as a least squares relaxation where the transform is obtained by minimizing a continuous optimization problem. The proposed approach is inherently parallelizable by performing independent optimization of each sphere using Gauss–Newton, and its least‐squares form allows it to be significantly more robust compared to traditional computational geometry approaches. Extensive experiments on 2D and 3D objects demonstrate that our method provides superior results to the state of the art on both synthetic and real‐data.

This paper introduces a novel methodology for residential building contouring from large-scale airborne point clouds. Unlike other methods that handle linearization and regularization of the linear primitives separately by imposing rigid constraints, we propose an optimization-based linearization and global regularization to form accurate, topologically error-free, and lightweight polygons. To this end, we enhance the classic density-based spatial clustering of applications with noise algorithm to segment individual building entities at the instance level. The initial contours of each individual building are then delineated and further decomposed by a novel topologically aware propagation process and a global optimization technique. The decomposed linear primitives are fed into the global regularization step, from which the regular shapes are learned and enforced hierarchically by imposing constraints, such as parallelism, homogeneity, orthogonality, and collinearity. Based on the concept of hybrid representation, the regularized and unaltered linear primitives are jointly connected in an esthetic way. Various experiments using representative buildings and large-scale residential scenes from the Dutch AHN3 data set have shown that the proposed methodology generates meaningful building contouring representation in terms of accuracy, compactness, topology, and levels of detail abstraction while being robust and scalable.

Abstract Buildings with symmetrical façades are ubiquitous in urban landscapes and detailed models of these buildings enhance the visual realism of digital urban scenes. However, a vast majority of the existing urban building models in web‐based 3D maps such as Google earth are either less detailed or heavily rely on texturing to render the details. We present a new framework for enhancing the details of such coarse models, using the geometry and symmetry inferred from the light detection and ranging (LiDAR) scans and 2D templates. The user‐defined 2D templates, referred to as coded planar meshes (CPMs), encodes the geometry of the smallest repeating 3D structures of the façades via face codes. Our encoding scheme, take into account the directions, type as well as the offset distance of the sculpting to be applied at the respective locations on the coarse model. In our approach, LiDAR scan is registered with the coarse models taken from Google earth 3D or Bing maps 3D and decomposed into dominant planar segments (each representing the frontal or lateral walls of the building). The façade segments are then split into horizontal and vertical tiles using a weighted point count function defined over the window or door boundaries. This is followed by an automatic identification of CPM locations with the help of a template fitting algorithm that respects the alignment regularity as well as the inter‐element spacing on the façade layout. Finally, 3D boolean sculpting operations are applied over the boxes induced by CPMs and the coarse model, and a detailed 3D model is generated. The proposed framework is capable of modelling details even with occluded scans and enhances not only the frontal façades (facing to the streets) but also the lateral façades of the buildings. We demonstrate the potentials of the proposed framework by providing several examples of enhanced Google earth models and highlight the advantages of our method when designing photo‐realistic urban façades.

This paper presents a novel topologically aware 2.5-D building modeling methodology from airborne laser scanning point clouds. The building reconstruction process consists of three main steps: primitive clustering, boundary representation, and geometric modeling. In primitive clustering, we propose an enhanced probability density clustering algorithm to cluster the rooftop primitives by taking into account the topological consistency among primitives. In the second step, we employ a novel Voronoi subgraph-based algorithm to seamlessly trace the primitive boundaries. This algorithm guarantees the production of geometric models without crack defects among adjacent primitives. The primitive boundaries are further divided into multiple linear segments, from which the key points are generated. These key points help to form a hybrid representation of the boundary by combining the projected points with part of the original boundary points. The model representation by the hybrid key points is flexible and well captures the rooftop details to generate lightweight and highly regular building models. Finally, we assemble the primitive boundaries to form the topologically correct entities, which are regarded as the basic units for primitive triangulation. The reconstructed models not only have accurate geometry and correct topology but more importantly have abundant semantics, by which five levels of building models can be generated in real time. The proposed reconstruction method has been comprehensively evaluated on Toronto data set in terms of model compactness, multilevel model representation, and geometric accuracy.