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用于点采样几何的曲率感知自适应重采样
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随着高分辨率3D扫描设备获取的大规模点采样几何的出现,开发有效的算法来处理这类具有大量几何细节和复杂拓扑的模型变得越来越重要。 作为预处理步骤,表面简化对于后续操作和几何处理非常重要,也是必需的。 基于自适应均值漂移聚类方案,提出了一种曲率感知的自适应重采样方法,用于点采样几何简化。 生成的采样点是非均匀分布的,并且可以以曲率感知的方式考虑局部几何特征,即在简化模型中,采样点在高曲率区域中密集,而在低曲率区域中稀疏。 所提出的方法已经实现并通过几个示例进行了演示。
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Computer-Aided Design 41 (2009) 395–403
Contents lists available at ScienceDirect
Computer-Aided Design
journal homepage: www.elsevier.com/locate/cad
Curvature-aware adaptive re-sampling for point-sampled geometry
Yongwei Miao
a,b,c,∗
, Renato Pajarola
c
, Jieqing Feng
a
a
State Key Laboratory of CAD&CG, Zhejiang University, China
b
College of Science, Zhejiang University of Technology, China
c
Department of Informatics, University of Zurich, Switzerland
a r t i c l e i n f o
Article history:
Received 14 April 2008
Accepted 22 January 2009
Keywords:
Point-sampled geometry
Adaptive re-sampling
Simplification
Curvature-aware
Mean-shift clustering
a b s t r a c t
With the emergence of large-scale point-sampled geometry acquired by high-resolution 3D scanning
devices, it has become increasingly important to develop efficient algorithms for processing such models
which have abundant geometric details and complex topology in general. As a preprocessing step, surface
simplification is important and necessary for the subsequent operations and geometric processing. Owing
to adaptive mean-shift clustering scheme, a curvature-aware adaptive re-sampling method is proposed
for point-sampled geometry simplification. The generated sampling points are non-uniformly distributed
and can account for the local geometric feature in a curvature aware manner, i.e. in the simplified model
the sampling points are dense in the high curvature regions, and sparse in the low curvature regions. The
proposed method has been implemented and demonstrated by several examples.
© 2009 Elsevier Ltd. All rights reserved.
1. Introduction
With the rapid development of various 3D scanning devices,
point-sampled geometry has become a powerful alternative to
the traditional polygonal geometric model in computer graphics
[1–3]. Efficient modeling and rendering techniques for the point-
sampled geometry have developed into an attractive research
area for its potential ability in representing complex geometric
models with high-fidelity [4–6]. However, due to the large memory
requirement and high time complexity, efficiently processing large
scale point-sampled geometry is still facing great challenges, such
as storage, editing, transmission, and rendering, etc. To achieve
real-time performance required in many application fields such
as entertainment, industrial design, virtual reality etc. [7,8], a
simplification procedure is an efficient solution to alleviate the
storage and time complexities.
In the point-sampled geometry simplification, it is important
to choose the representative points and re-sampling the original
geometry for faithfully approximating the underlying geometry
in both geometry and topology. In practical applications, how to
keep geometric features may attract more attentions since it is
a comparably simple task to keep the simplified model topology
unchanged. Thus, pursuing the geometry fidelity of the simplified
model, the sampling density variation should manifest the local
geometric features, i.e. the sample points should be dense in
the sharp features regions (usually with high curvatures), and
∗
Corresponding author.
E-mail addresses: miaoyw@cad.zju.edu.cn, ywmiao@zjut.edu.cn (Y. Miao).
sparse in the relative planar regions (usually with low curvatures).
Another important issue that relates to surface re-sampling is
the theoretical analysis of sampling conditions and other pre-
conditions for correct reconstruction of surfaces with or without
boundaries [9–11].
Owing to the efficiency of feature space analysis, a mean-shift
scheme is performed in both spatial and range domain of the
underlying geometry. Due to the bilateral filtering property of our
mean-shift clustering scheme, the proposed re-sampling approach
can filter moderate noise attached by the given model. Moreover,
in order to guide a feature sensitive re-sampling procedure,
unlike the fixed bandwidth mean-shift clustering, the proposed
adaptive scheme is suitable for the moderately non-uniformly
distributed point-sampled geometry. However, point clouds with
highly non-uniform sampling or large noise cannot be treated well
by our algorithm. For these raw scanner data, some pre-processing
steps [12] should be performed for subsequent re-sampling task.
The contributions are summarized as follows:
• Based on an adaptive mean-shift clustering scheme, a novel
point-sampled geometry simplification method is proposed,
which can adaptively re-sample the underlying model so as
to reflect the intrinsic geometry features whilst introducing
relatively lower geometric error.
• By choosing different thresholds and different weights in
our mean-shift clustering scheme, the adaptive re-sampling
scheme can adapt to different sampling density requirements
of the underlying point-sampled geometry.
0010-4485/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.cad.2009.01.006
396 Y. Miao et al. / Computer-Aided Design 41 (2009) 395–403
• Our simplification scheme is time efficient and easy to
implement. It allows direct processing of scanned data without
the need to construct polygonal meshes beforehand, leading to
an increased overall performance.
The paper is organized as follows. The related work on simpli-
fication and re-sampling methods for point-sampled geometry is
reviewed in Section 2. In Section 3, an adaptive mean-shift scheme
is proposed to analyze the local maxima of a multivariate probabil-
ity density function. Based on the mean-shift analysis, an adaptive
re-sampling approach for the point-sampled geometry is described
in Section 4. In Section 5, some experimental results are listed and
the geometric error analysis by our re-sampling scheme is given.
Finally, conclusions are drawn and directions for future research
are given in Section 6.
2. Related work
Surface simplification and re-sampling. Many pieces of work
related to point-sampled geometry simplification and re-sampling
have been proposed in digital geometry processing, such as
extrinsic Voronoi diagram-based scheme, intrinsic technique, grid-
based and statistical-based approach, incremental and hierarchical
clustering scheme, iterative simplification method, and particle-
based re-sampling approach, etc.
Dey et al. [13] presented a dedicated point cloud simplification
algorithm using the particular structure of 3D Voronoi cells of a
dense point cloud. It is a locally restricted method and cannot
handle the non-uniformly distributed point clouds or point clouds
with holes. Moenning and Dodgson [14,15] presented an intrinsic
coarse-to-fine simplification algorithm with sampling density
guarantee for point clouds. However, their algorithm requires the
complicated computation of intrinsic geodesic Voronoi diagrams.
Linsen [2] proposed a point set simplification scheme that
associated each input sample point with an information content
measure and then iteratively removed points with lowest entropy.
This re-sampling algorithm is only limited to the generation of
point cloud subsets and cannot give any density guarantee.
Kalaiah and Varshney [16] described a statistical-based ge-
ometry representation scheme, which can contribute to reduce
network bandwidth and to high-quality interactive rendering
without sacrificing visual realism. Nehab and Shilane [17] pro-
posed a grid-based stratified sampling strategy for 3D models,
which first voxelizes the underlying model and then selects one
sample point for each voxel. However, these surface simplification
approaches cannot sample the given 3D model to indicate its local
geometric features exactly.
Due to the comprehensive research on mesh simplification
[18–21], many greedy and local clustering mesh simplification
schemes can be directly extended to point-sampled geometry.
However, major difficulties for the direct extension are how
to control the re-sampling density, and the approximation
error for simplifying point-sampled geometry. Pauly et al. [7]
adopted uniform incremental clustering and adaptive hierarchical
clustering methods to simplify a given point cloud. The uniform
incremental clustering approach is computationally efficient but
is reported to cause high approximation error. Similarly, the
hierarchical clustering approach is memory and execution efficient
but even in its adaptive version the approximation error is not very
low in general. Similar to the error-controlled mesh simplification
scheme [18], Pauly et al. [7] also presented an iterative scheme to
produce an optimal result in terms of average geometric accuracy.
But it is not intuitive for the point set density control. Wu et al. [8]
re-sample a given dense point set by a sparse set of circular or
elliptical object-space splats. Nevertheless, the generation of initial
splat candidates and guarantee of the simplified model of being
free of holes are time-consuming.
Recently, particle simulation has become a popular approach
for simplifying large-scale 3D models. Early in 1992, Turk [22]
introduced a mesh re-sampling method via particle simulation.
The particles with a specified number are randomly spread across
the surface and they are approximately equal-distance distributed
by using a point repulsion algorithm according to their curvature
estimation. Witkin and Heckbert [23] used an adaptive repulsion
and split-and-death criteria to scatter a particle system on an
implicit surface which minimizes an energy criterion. Hart et al.
[24] extended the method of Witkin and Heckbert to uniformly
sample and control the more complex implicit surfaces. Pauly
et al. [7] adopt particle simulation to simplify the point-sampled
geometry by considering approximation accuracy and density
controls. Recently, Proenca et al. [25] achieved non-uniform
sampling MPU implicit surface according to the model features,
i.e. high densities in the abundant feature areas and vice versa. In
general, the particle simulation is a computationally demanding
approach and is not efficient enough for the large-scale point-
sampled models.
Local surface differentials estimation. In order to obtain the
splats for each cluster produced by our technique, an important
step of our algorithm is to estimate the local surface differentials.
A detailed overview of surface differentials estimation algorithms
can be found in recent papers [26,27] and the references therein.
Taubin [28] proposed a integral eigenvalue method to estimate
the tensor of curvature using a one-ring neighborhood. Hameiri
and Shimsoni [29] presented a modification of Taunbin’s method
by expanding to all the neighbor points inside a given radius
across the normal sections for stable principal curvature estimate
on discrete noisy range data. Applying the principal component
analysis (PCA) method to the neighborhoods of sample points,
Pauly et al. [7] proposed an algorithm to estimate normals and
curvatures for point-sampled geometry. Translating from Taubin’s
method, Lange and Polthier [30] derived a similar method for
estimating principal curvatures and principal curvature directions
for point set surfaces.
The idea of surface fitting is always applied to estimate
surface features. To calculate surface differentials analytically,
the quadratic or cubic polynomial fitting is adopted to find
an implicit representation that fits the geometry locally [31,
32]. Cazals and Pouget [33] proposed a method to estimate
local surface differentials by polynomial fitting of an osculating
jet. Rusinkiewicz [34] presented an algorithm to estimate the
curvature tensor by least-squares fitting to the normal variations.
Also using local least square fitting, Mitra et al. [35] described
a method for estimating the normals at all sample points of a
point cloud data set. Tong and Tang [36] proposed a tensor voting
technique to robustly estimate curvature tensors. Based on Levin’s
moving least square (MLS) approximation method [37], Alexa and
Adamson [38] adopted the gradient of the local implicit surface
as an accurate surface normal estimate and presented efficient
orthogonal projection operators for sampling theory. Based on the
explicit definition for point-set surfaces [39], Yang and Qian [40]
proposed a direct computing scheme for surface curvatures.
Recently, based on curvature tensor fitting, Kalogerakis et al.
[26] proposed a robust statistical framework for curvature
estimate on discretely sampled surfaces. Miao et al. [41] proposed
a projection scheme to estimate local surface differentials for the
point-sampled geometry. All of the sample points in the neighbors
are projected onto the normal plane, and the two principal
directions and curvatures can be obtained by normal curvature
analysis regarding to only three sampled tangent directions.
In our implementation, we use the projection scheme [41] to
estimate the principal directions and curvatures as it provides an
efficient estimation of the principal directions and curvatures for
point-set surfaces. However, our re-sampling method is not strictly
dependent on this specific curvature estimate algorithm and other
techniques also can be used instead.
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