Ruqi Huang

Beyond Talking – Generating Holistic 3D Human Dyadic Motion for Communication

Mingze Sun, Chao Xu, Xinyu Jiang, Yang Liu, Baigui Sun, Ruqi Huang

Abstract: In this paper, we introduce an innovative task focused on human communication, aiming to generate 3D holistic human motions for both speakers and listeners. Central to our approach is the incorporation of factorization to decouple audio features and the combination of textual semantic information, thereby facilitating the creation of more realistic and coordinated movements. We separately train VQ-VAEs with respect to the holistic motions of both speaker and listener. We consider the real-time mutual influence between the speaker and the listener and propose a novel chain-like transformer-based auto-regressive model specifically designed to characterize real-world communication scenarios effectively which can generate the motions of both the speaker and the listener simultaneously. These designs ensure that the results we generate are both coordinated and diverse. Our approach demonstrates state-of-the-art performance on two benchmark datasets. Furthermore, we introduce the HoCo holistic communication dataset, which is a valuable resource for future research. Our HoCo dataset and code will be released for research purposes upon acceptance.

International Journal of Computer Vision, 2024

[pdf 2.1M]

SRIF: Semantic Shape Registration Empowered by Diffusion-based Image Morphing and Flow Estimation

Mingze Sun, Chen Guo, Puhua Jiang, Shiwei Mao, Yurun Chen, Ruqi Huang

Abstract: In this paper, we propose SRIF, a novel Semantic shape Registration framework based on diffusion-based Image morphing and Flow estimation. More concretely, given a pair of extrinsically aligned shapes, we first render them from multi-views, and then utilize an image interpolation framework based on diffusion models to generate sequences of intermediate images between them. The images are later fed into a dynamic 3D Gaussian splatting framework, with which we reconstruct and post-process for intermediate point clouds respecting the image morphing processing. In the end, tailored for the above, we propose a novel registration module to estimate continuous normalizing flow, which deforms source shape consistently towards the target, with intermediate point clouds as weak guidance. Our key insight is to leverage large vision models (LVMs) to associate shapes and therefore obtain much richer semantic information on the relationship between shapes than the ad-hoc feature extraction and alignment. As consequence, SRIF achieves high-quality dense correspondences on challenging shape pairs, but also delivers smooth, semantically meaningful interpolation in between. Empirical evidences justify the effectiveness and superiority of our method as well as specific design choices.

Proc. SIGGRAPH Asia, 2024

[pdf 3.2M] [BibTex]

Enhancing Human Optical Flow via 3D Spectral Prior

Shiwei Mao, Mingze Sun, Ruqi Huang

Abstract: In this paper, we consider the problem of human optical flow estimation, which is critical in a series of human-centric computer vision tasks. Recent deep learning-based optical flow models have achieved considerable accuracy and generalization by incorporating various kinds of priors. However, the majority either rely on large-scale 2D annotations or rigid priors, overlooking the 3D non-rigid nature of human articulations. To this end, we advocate enhancing human optical flow estimation via 3D spectral prior-aware pretraining, which is based on the well-known functional maps formulation in 3D shape matching. Our pretraining can be performed with synthetic human shapes. More specifically, we first render shapes to images and then leverage the natural inclusion maps from images to shapes to lift 2D optical flow into 3D correspondences, which are further encoded as functional maps. Such lifting operation allows to inject the intrinsic geometric features encoded in the spectral representations into optical flow learning, leading to improvement of the latter, especially in the presence of non-rigid deformations. In practice, we establish a pretraining pipeline tailored for triangular meshes, which is general regarding target optical flow network. It is worth noting that it does not introduce any additional learning parameters but only require some pre-computed eigen decomposition on the meshes. For RAFT and GMA, our pretraining task achieves improvements of 12.8% and 4.9% in AEPE on the SHOF benchmark, respectively.

Proc. Pacific Graphics, 2024

[pdf 7.7M]

Nanowatt all-optical 3D perception for mobile robotics

Tao Yan, Tiankuang Zhou, Yanchen Guo, Yun Zhao, Guocheng Shao, Jiamin Wu, Ruqi Huang, Qionghai Dai, Lu Fang

Abstract: Three-dimensional (3D) perception is vital to drive mobile robotics’ progress toward intelligence. However, state-of-the-art 3D perception solutions require complicated postprocessing or point-by-point scanning, suffering computational burden, latency of tens of milliseconds, and additional power consumption. Here, we propose a parallel all-optical computational chipset 3D perception architecture (Aop3D) with nanowatt power and light speed. The 3D perception is executed during the light propagation over the passive chipset, and the captured light intensity distribution provides a direct reflection of the depth map, eliminating the need for extensive postprocessing. The prototype system of Aop3D is tested in various scenarios and deployed to a mobile robot, demonstrating unprecedented performance in distance detection and obstacle avoidance. Moreover, Aop3D works at a frame rate of 600 hertz and a power consumption of 33.3 nanowatts per meta-pixel experimentally. Our work is promising toward next-generation direct 3D perception techniques with light speed and high energy efficiency.

Science Advances, 2024

[pdf] [BibTex]

XScale-NVS: Cross-Scale Novel View Synthesis with Hash Featurized Manifold

Guangyu Wang, Jinzhi Zhang, Fan Wang, Ruqi Huang, Lu Fang

Abstract: We propose XScale-NVS for high-fidelity cross-scale novel view synthesis of real-world large-scale scenes. Existing representations based on explicit surface suffer from discretization resolution or UV distortion, while implicit volumetric representations lack scalability for large scenes due to the dispersed weight distribution and surface ambiguity. In light of the above challenges, we introduce hash featurized manifold, a novel hash-based featurization coupled with a deferred neural rendering framework. This approach fully unlocks the expressivity of the representation by explicitly concentrating the hash entries on the 2D manifold, thus effectively representing highly detailed contents independent of the discretization resolution. We also introduce a novel dataset, namely GigaNVS, to benchmark cross-scale, high-resolution novel view synthesis of realworld large-scale scenes. Our method significantly outperforms competing baselines on various real-world scenes, yielding an average LPIPS that is ∼ 40% lower than prior state-of-the-art on the challenging GigaNVS benchmark.

Proc. IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2024

[pdf 8.9M] [BibTex]

OmniSeg3D: Omniversal 3D Segmentation via Hierarchical Contrastive Learning

Haiyang Ying, Yixuan Yin, Jinzhi Zhang, Fan Wang, Tao Yu, Ruqi Huang, Lu Fang

Abstract: Towards holistic understanding of 3D scenes, a general 3D segmentation method is needed that can segment diverse objects without restrictions on object quantity or categories, while also reflecting the inherent hierarchical structure. To achieve this, we propose OmniSeg3D, an omniversal segmentation method aims for segmenting anything in 3D all at once. The key insight is to lift multi-view inconsistent 2D segmentations into a consistent 3D feature field through a hierarchical contrastive learning framework, which is accomplished by two steps. Firstly, we design a novel hierarchical representation based on category-agnostic 2D segmentations to model the multi-level relationship among pixels. Secondly, image features rendered from the 3D feature field are clustered at different levels, which can be further drawn closer or pushed apart according to the hierarchical relationship between different levels. In tackling the challenges posed by inconsistent 2D segmentations, this framework yields a global consistent 3D feature field, which further enables hierarchical segmentation, multi-object selection, and global discretization. Extensive experiments demonstrate the effectiveness of our method on high-quality 3D segmentation and accurate hierarchical structure understanding. A graphical user interface further facilitates flexible interaction for omniversal 3D segmentation.

Proc. IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2024

[pdf 9.0M] [BibTex]

Non-Rigid Shape Registration via Deep Functional Maps Prior

Puhua Jiang, Mingze Sun, Ruqi Huang

Abstract: In this paper, we propose a learning-based framework for non-rigid shape registration without correspondence supervision. Traditional shape registration techniques typically rely on correspondences induced by extrinsic proximity, therefore can fail in the presence of large intrinsic deformations. Spectral mapping methods overcome this challenge by embedding shapes into, geometric or learned, highdimensional spaces, where shapes are easier to align. However, due to the dependency on abstract, non-linear embedding schemes, the latter can be vulnerable with respect to perturbed or alien input. In light of this, our framework takes the best of both worlds. Namely, we deform source mesh towards the target point cloud, guided by correspondences induced by high-dimensional embeddings learned from deep functional maps (DFM). In particular, the correspondences are dynamically updated according to the intermediate registrations and filtered by consistency prior, which prominently robustify the overall pipeline. Moreover, in order to alleviate the requirement of extrinsically aligned input, we train an orientation regressor on a set of aligned synthetic shapes independent of the training shapes for DFM. Empirical results show that, with as few as dozens of training shapes of limited variability, our pipeline achieves state-of-the-art results on several benchmarks of non-rigid point cloud matching, but also delivers high-quality correspondences between unseen challenging shape pairs that undergo both significant extrinsic and intrinsic deformations, in which case neither traditional registration methods nor intrinsic methods work.

Proc. 37th Conference on Neural Information Processing Systems (NeurIPS 2023)

[pdf 9.9M] [code] [BibTex]

GiganticNVS: Gigapixel Large-scale Neural Rendering with Implicit Meta-deformed Manifold

Guangyu Wang, Jinzhi Zhang, Kai Zhang, Ruqi Huang, Lu Fang

Abstract: The rapid advances of high-performance sensation empowered gigapixel-level imaging/videography for large-scale scenes, yet the abundant details in gigapixel images were rarely valued in 3d reconstruction solutions. Bridging the gap between the sensation capacity and that of reconstruction requires to attack the large-baseline challenge imposed by the large-scale scenes, while utilizing the high-resolution details provided by the gigapixel images. This paper introduces GiganticNVS for gigapixel large-scale novel view synthesis (NVS). Existing NVS methods suffer from excessively blurred artifacts and fail on the full exploitation of image resolution, due to their inefficacy of recovering a faithful underlying geometry and the dependence on dense observations to accurately interpolate radiance. Our key insight is that, a highly-expressive implicit field with view-consistency is critical for synthesizing high-fidelity details from large-baseline observations. In light of this, we propose meta-deformed manifold, where meta refers to the locally defined surface manifold whose geometry and appearance are embedded into high-dimensional latent space. Technically, meta can be decoded as neural fields using an MLP (i.e., implicit representation). Upon this novel representation, multi-view geometric correspondence can be effectively enforced with featuremetric deformation and the reflectance field can be learned purely on the surface. Experimental results verify that the proposed method outperforms state-of-the-art methods both quantitatively and qualitatively, not only on the standard datasets containing complex real-world scenes with large baseline angles, but also on the challenging gigapixel-level ultra-large-scale benchmarks.

IEEE Transactions on Pattern Analysis and Machine Intelligence (TPAMI), 2023

[pdf 2.4M] [BibTex]

Spatially and Spectrally Consistent Deep Functional Maps

Mingze Sun, Shiwei Mao, Puhua Jiang, Maks Ovsjanikov, Ruqi Huang

Abstract: Cycle consistency has long been exploited as a powerful prior for jointly optimizing maps within a collection of shapes. In this paper, we investigate its utility in the approaches of Deep Functional Maps, which are considered state-of-the-art in non-rigid shape matching. We first justify that under certain conditions, the learned maps, when represented in the spectral domain, are already cycle consistent. Furthermore, we identify the discrepancy that spectrally consistent maps are not necessarily spatially, or point-wise, consistent. In light of this, we present a novel design of unsupervised Deep Functional Maps, which effectively enforces the harmony of learned maps under the spectral and the point-wise representation. By taking advantage of cycle consistency, our framework produces stateof- the-art results in mapping shapes even under significant distortions. Beyond that, by independently estimating maps in both spectral and spatial domains, our method naturally alleviates over-fitting in network training, yielding superior generalization performance and accuracy within an array of challenging tests for both near-isometric and nonisometric datasets.

Proc. International Conference on Computer Vision (ICCV), 2023

[pdf 16.6M] [code] [poster 9.2M] [BibTex]

RealGraph: A Multiview Dataset for 4D Real-world Context Graph Generation

Haozhe Lin, Zequn Chen, Jinzhi Zhang, Bing Bai, Yu Wang, Ruqi Huang, Lu Fang

Abstract: Understanding 4D scene context in real world has become urgently critical for deploying sophisticated AI systems. In this paper, we propose a brand new scene understanding paradigm called “Context Graph Generation (CGG)”, aiming at abstracting holistic semantic information in the complicated 4D world. The CGG task capitalizes on the calibrated multiview videos of a dynamic scene, and targets at recovering semantic information (coordination, trajectories and relationships) of the presented objects in the form of spatio-temporal context graph in 4D space. We also present a benchmark 4D video dataset “RealGraph”, the first dataset tailored for the proposed CGG task. The raw data of RealGraph is composed of calibrated and synchronized multiview videos. We exclusively provide manual annotations including object 2D&3D bounding boxes, category labels and semantic relationships. We also make sure the annotated ID for every single object is temporally and spatially consistent. We propose the first CGG baseline algorithm, Multiview-based Context Graph Generation Network (MCGNet), to empirically investigate the legitimacy of CGG task on RealGraph dataset. We nevertheless reveal the great challenges behind this task and encourage the community to explore beyond our solution.

Proc. International Conference on Computer Vision (ICCV), 2023

[pdf 2.0M] [BibTex]

The Group Interaction Field for Learning and Explaining Pedestrian Anticipation

Xueyang Wang, Xuecheng Chen, Puhua Jiang, Haozhe Lin, Xiaoyun Yuan, Mengqi Ji, Yuchen Guo, Ruqi Huang, Lu Fang

Abstract: Anticipating others’ actions is innate and essential in order for humans to navigate and interact well with others in dense crowds. This ability is urgently required for unmanned systems such as service robots and self-driving cars. However, existing solutions struggle to predict pedestrian anticipation accurately, because the influence of group-related social behaviors has not been well considered. While group relationships and group interactions are ubiquitous and significantly influence pedestrian anticipation, their influence is diverse and subtle, making it difficult to explicitly quantify. Here, we propose the group interaction field (GIF), a novel group-aware representation that quantifies pedestrian anticipation into a probability field of pedestrians’ future locations and attention orientations. An end-to-end neural network, GIFNet, is tailored to estimate the GIF from explicit multidimensional observations. GIFNet quantifies the influence of group behaviors by formulating a group interaction graph with propagation and graph attention that is adaptive to the group size and dynamic interaction states. The experimental results show that the GIF effectively represents the change in pedestrians’ anticipation under the prominent impact of group behaviors and accurately predicts pedestrians’ future states. Moreover, the GIF contributes to explaining various predictions of pedestrians’ behavior in different social states. The proposed GIF will eventually be able to allow unmanned systems to work in a human-like manner and comply with social norms, thereby promoting harmonious human–machine relationships.

Engineering, 2023

[pdf 3.6M] [BibTex]

Neural Intrinsic Embedding for Non-rigid Point Cloud Matching

Puhua Jiang, Mingze Sun, Ruqi Huang

Abstract: As a primitive 3D data representation, point clouds are prevailing in 3D sensing, yet short of intrinsic structural information of the underlying objects. Such discrepancy poses great challenges on directly establishing correspondences between point clouds sampled from deformable shapes. In light of this, we propose Neural Intrinsic Embedding (NIE) to embed each vertex into a high-dimensional space in a way that respects the intrinsic structure. Based upon NIE, we further present a weakly-supervised learning framework for non-rigid point cloud registration. Unlike the prior works, we do not require expansive and sensitive off-line basis construction (e.g., eigen-decomposition of Laplacians), nor do we require ground-truth correspondence labels for supervision. We empirically show that our framework performs on par with or even better than the state-of-the-art baselines, which generally require more supervision and/or more structural geometric input.

Proc. IEEE Conference on Computer Vision and Pattern Recognition (CVPR), 2023

[pdf 6.5M] [code] [poster 2.4M] [BibTex]

Optical Neural Ordinary Differential Equations

Yun Zhao, Hang Chen, Min Lin, Haiou Zhang, Tao Yan, Xing Lin, Ruqi Huang, Qionghai Dai

Abstract: Increasing the layer number of on-chip photonic neural networks (PNNs) is essential to improve its model performance. However, the successively cascading of network hidden layers results in larger integrated photonic chip areas. To address this issue, we propose the optical neural ordinary differential equations (ON-ODE) architecture that parameterizes the continuous dynamics of hidden layers with optical ODE solvers. The ON-ODE comprises the PNNs followed by the photonic integrator and optical feedback loop, which can be configured to represent residual neural networks (ResNet) and recurrent neural networks with effectively reduced chip area occupancy. For the interference-based optoelectronic nonlinear hidden layer, the numerical experiments demonstrate that the single hidden layer ON-ODE can achieve approximately the same accuracy as the two-layer optical ResNet in image classification tasks. Besides, the ON-ODE improves the model classification accuracy for the diffraction-based all-optical linear hidden layer. The time-dependent dynamics property of ON-ODE is further applied for trajectory prediction with high accuracy.

Optics Letters, 2023

[pdf 1.0M] [BibTex]

ElasticMVS: Learning elastic part representation for self-supervised multi-view stereopsis

Jinzhi Zhang, Ruofan Tang, Zheng Cao, Jing Xiao, Ruqi Huang, Lu Fang

Abstract: Learning dense surface predictions from only a set of images without onerous groundtruth 3D training data for supervision. However, existing methods highly rely on the local photometric consistency, which fail to identify accurately dense correspondence in broad textureless or reflectant areas. In this paper, we show that geometric proximity such as surface connectedness and occlusion boundaries implicitly inferred from images could serve as reliable guidance for pixel-wise multi-view correspondences. With this insight, we present a novel elastic part representation, which encodes physically-connected part segmentations with elastically-varying scales, shapes and boundaries. Meanwhile, a self-supervised MVS framework namely ElasticMVS is proposed to learn the representation and estimate per-view depth following a part-aware propagation and evaluation scheme. Specifically, the pixel-wise part representation is trained by a contrastive learning-based strategy, which increases the representation compactness in geometrically concentrated areas and contrasts otherwise. ElasticMVS iteratively optimizes a part-level consistency loss and a surface smoothness loss, based on a set of depth hypotheses propagated from the geometrically concentrated parts. Extensive evaluations convey the superiority of ElasticMVS in the reconstruction completeness and accuracy, as well as the efficiency and scalability. Particularly, for the challenging large-scale reconstruction benchmark, ElasticMVS demonstrates significant performance gain over both the supervised and self-supervised approaches.

Proc. Conference on Neural Information Processing Systems (NeurIPS) (Spotlight), 2022

[pdf 6.5M] [BibTex]

ParseMVS: Learning Primitive-aware Surface Representations for Sparse Multi-view Stereopsis

Haiyang Ying, Jinzhi Zhang, Yuzhe Chen, Zheng Cao, Jing Xiao, Ruqi Huang, Lu Fang

Abstract: Multi-view stereopsis (MVS) recovers 3D surfaces by finding dense photo-consistent correspondences from densely sampled images. In this paper, we tackle the challenging MVS task from sparsely sampled views (up to an order of magnitude fewer images), which is more practical and cost-efficient in applications. The major challenge comes from the significant correspondence ambiguity introduced by the severe occlusions and the highly skewed patches. On the other hand, such ambiguity can be resolved by incorporating geometric cues from the global structure. In light of this, we propose ParseMVS, boosting sparse MVS by learning the Primitive-AwaRe Surface rEpresentation. In particular, on top of being aware of global structure, our novel representation further allows for the preservation of fine details including geometry, texture, and visibility. More specifically, the whole scene is parsed into multiple geometric primitives. On each of them, the geometry is defined as the displacement along the primitives’ normal directions, together with the texture and visibility along each view direction. An unsupervised neural network is trained to learn these factors by progressively increasing the photo-consistency and render-consistency among all input images. Since the surface properties are changed locally in the 2D space of each primitive, ParseMVS can preserve global primitive structures while optimizing local details, handling the ‘incompleteness’ and the ‘inaccuracy’ problems.We experimentally demonstrate that ParseMVS constantly outperforms the state-ofthe- art surface reconstruction method in both completeness and the overall score under varying sampling sparsity, especially under the extreme sparse-MVS settings. Beyond that, ParseMVS also shows great potential in compression, robustness, and efficiency.

Proc. ACM International Conference on Multimedia, 2022

[pdf 22.5M] [BibTex]

Consistent ZoomOut: Efficient Spectral Map Synchronization

Ruqi Huang, Jing Ren, Peter Wonka, Maks Ovsjanikov

Abstract: In this paper, we propose a novel method, which we call CONSISTENT ZOOMOUT, for efficiently refining correspondences among deformable 3D shape collections, while promoting the resulting map consistency. Our formulation is closely related to a recent unidirectional spectral refinement framework, but naturally integrates map consistency constraints into the refinement. Beyond that, we show further that our formulation can be adapted to recover the underlying isometry among near-isometric shape collections with a theoretical guarantee, which is absent in the other spectral map synchronization frameworks. We demonstrate that our method improves the accuracy compared to the competing methods when synchronizing correspondences in both near-isometric and heterogeneous shape collections, but also significantly outperforms the baselines in terms of map consistency.

Proc. Symposium on Geometry Processing, 2020

[pdf 1.2M] [code] [video] [BibTex]

OperatorNet: Recovering 3D Shapes From Difference Operators

Ruqi Huang, Marie-Julie Rakotosaona, Panos Achlioptas, Leonidas Guibas, Maks Ovsjanikov

Abstract: This paper proposes a learning-based framework for reconstructing 3D shapes from functional operators, compactly encoded as small-sized matrices. To this end we introduce a novel neural architecture, called OperatorNet, which takes as input a set of linear operators representing a shape and produces its 3D embedding. We demonstrate that this approach significantly outperforms previous purely geometric methods for the same problem. Furthermore, we introduce a novel functional operator, which encodes the extrinsic or pose-dependent shape information, and thus complements purely intrinsic pose-oblivious operators, such as the classical Laplacian. Coupled with this novel operator, our reconstruction network achieves very high reconstruction accuracy, even in the presence of incomplete information about a shape, given a soft or functional map expressed in a reduced basis. Finally, we demonstrate that the multiplicative functional algebra enjoyed by these operators can be used to synthesize entirely new unseen shapes, in the context of shape interpolation and shape analogy applications.

Proc. International Conference on Computer Vision(ICCV), 2019

[pdf 13.1M] [code] [BibTex]

Limit Shape – A Tool for Understanding Shape Differences and Variablity in 3D Model Collections

Ruqi Huang, Panos Achlioptas, Leonidas Guibas, Maks Ovsjanikov

Abstract: We propose a novel construction for extracting a central or limit shape in a shape collection, connected via a functional map network. Our approach is based on enriching the latent space induced by a functional map network with an additional natural metric structure. We call this shape-like dual object the limit shape and show that its construction avoids many of the biases introduced by selecting a fixed base shape or template. We also show that shape differences between real shapes and the limit shape can be computed and characterize the unique properties of each shape in a collection – leading to a compact and rich shape representation. We demonstrate the utility of this representation in a range of shape analysis tasks, including improving functional maps in difficult situations through the mediation of limit shapes, understanding and visualizing the variability within and across different shape classes, and several others. In this way, our analysis sheds light on the missing geometric structure in previously used latent functional spaces, demonstrates how these can be addressed and finally enables a compact and meaningful shape representation useful in a variety of practical applications.

Proc. Symposium on Geometry Processing, 2019

[pdf 1.5M] [code] [BibTex]

Adjoint Map Representation for Shape Analysis and Matching

Ruqi Huang, Maks Ovsjanikov

Abstract: In this paper, we propose to consider the adjoint operators of functional maps, and demonstrate their utility in several tasks in geometry processing. Unlike a functional map, which represents a correspondence simply using the pull-back of function values, the adjoint operator reflects both the map and its distortion with respect to given inner products. We argue that this property of adjoint operators and especially their relation to the map inverse under the choice of different inner products, can be useful in applications including bi-directional shape matching, shape exploration, and pointwise map recovery among others. In particular, in this paper, we show that the adjoint operators can be used within the cycle-consistency framework to encode and reveal the presence or lack of consistency between distortions in a collection, in a way that is complementary to the previously used purely map-based consistency measures. We also show how the adjoint can be used for matching pairs of shapes, by accounting for maps in both directions, can help in recovering point-to-point maps from their functional counterparts, and describe how it can shed light on the role of functional basis selection.

Proc. Symposium on Geometry Processing, 2017

[pdf 18.6M] [code] [BibTex]

On the Stability of Functional Maps and Shape Difference Operators

Ruqi Huang, Frederic Chazal, Maks Ovsjanikov

Abstract: In this paper, we provide stability guarantees for two frameworks that are based on the notion of functional maps – the shape difference operators and the framework which is used to analyze and visualize the deformations between shapes induced by a functional map. We consider two types of perturbations in our analysis: one is on the input shapes and the other is on the change in scale. In theory, we formulate and justify the robustness that has been observed in practical implementations of those frameworks. Inspired by our theoretical results, we propose a pipeline for constructing shape difference operators on point clouds and show numerically that the results are robust and informative. In particular, we show that both the shape difference operators and the derived areas of highest distortion are stable with respect to changes in shape representation and change of scale. Remarkably, this is in contrast with the well-known instability of the eigenfunctions of the Laplace-Beltrami operator computed on point clouds compared to those obtained on triangle meshes.

Computer Graphics Forum, 2017

[pdf 18.5M] [BibTex]

Gromov-Hausdorff Approximation of Filamentary Structures Using Reeb-Type Graphs

Frederic Chazal, Ruqi Huang, Jian Sun

Abstract: In many real-world applications data appear to be sampled around 1-dimensional filamentary structures that can be seen as topological metric graphs. In this paper we address the metric reconstruction problem of such filamentary structures from data sampled around them. We prove that they can be approximated, with respect to the Gromov-Hausdorff distance by well-chosen Reeb graphs (and some of their variants) and provide an efficient and easy to implement algorithm to compute such approximations in almost linear time. We illustrate the performances of our algorithm on a few data sets.

Discrete Computational Geometry, 2015

[pdf 3.0M] [BibTex]