Abstract: As the technical development of laser scanning and image based modeling, more and more point cloud data are obtained to
represent 3D geometric shapes of natural objects. Calculation of differential properties of 3D discrete geometry becomes one
fundamental work. Through the relation of discrete normal curvatures and principal curvatures, a new algorithm is presented
on estimating the principal curvatures and principal directions 3D point cloud surface. Based on the local fitting of each
normal section circle properties with the position and the normal at a neighbor point, principal curvatures and principal
directions are estimated from the contribution of these neighbor points. Optimization of this estimation is converted as a
linear system by least squares fitting to all discrete normal curvatures corresponding to its neighbor points. A local feature
curve, called as normal curvature index lines, is constructed to show the efficiency of this work. This curve is intuitive and
equivalent to Dupin index line. Experiments are designed on Gaussian curvature, mean curvature and principal directions for
an analytical surface and discrete surfaces of point cloud data. Experimental results show that this work is more advantageous
than similar approaches, ad have applications to shape analysis and measurements.
Keywords: Normal section curvature, principal curvatures, principal directions, least squares fitting.
1. Introduction
In recent years, the increasing availability and power of
range scanners has enabled us to scan larger and more
complex objects, to obtain rich detail features of objects and
to get larger quantity of point cloud data, which is helpful to
the reconstruction of geometric objects, shape modeling and
shape feature analysis. Some basic differential geometric
properties should still be better estimated for object
reconstruction, shape modeling or analysis. Two of these
most important properties are the main curvatures together
with principal directions on an estimated surface. If points
are from a known analytic surface, the curvature at every
point can be precisely calculated by classic differential
geometric methods. However, if points were sampled from
an unknown surface, with a laser-canner for example,
estimating main curvatures and principal directions of every
point would be an interesting and challengeable topic.
Estimating curvatures of 3D B-Rep (Boundary
Representation) models has been cared since 1980s.
Conventional methods often include point cloud denoising,
mesh generation and curvature estimation. Some
preprocessing may be performed at first, such as denoising
and alignment. According to the mathematic tools adopted
for geometric models, these methods can be divided into
three categories. The first category is surface fitting with a
polynomial surface at a local area. The surface can be a
quadric surface [Sander1990; Stokely1992; Hamann1993;
Krsek1998; Krsek1997], a cubic surface [Goldfeather2004],
or a general polynomial surface. The second category is to
compute the curvatures at each vertex of a mesh model by
measuring the angle of each polygon passing through this
vertex [Dyn2001; Kim2001]. The third category is to
calculate the normal curvature of a direction from neighbor
points, and all the normal curvatures are weightily averaged
with central angle or with of tangent vectors [Taubin1995].
These methods work well for mesh models, and they can be
applied to point cloud model after an extension.
We will present a new fast method for point cloud
models, where both mesh reconstruction and surface fitting
are all avoided. Our method just uses neighbor points and
normal vectors to estimate the normal curvature, where a
normal section curve is thought of as spanned by one
neighbor point and corresponding normal vector there.
Principal curvatures and principal directions are estimated
through the least square fitting of all normal curvatures
related to all neighbor points. It can be shown that this new
approach is better to some degree than other similar methods,
and it can be sued for shape analysis and shape
measurements.
To show the effect of curvature estimation and to
compare different approaches, we will construct a new kind
of graph, called as normal curvature index lines, abbreviated
as NCIL. This graph is simple and intuitive. With NCIL, it
will be illustrated that our method is more precise and faster
than the method by Taubin [Taubin1995], and it is better
than the approach of Goldfeather [Goldfeather2004] also.
The organization of this paper is as flows. State-of-art
work of this topic is described in Session 2. The main
algorithm is reasoned and described in Session 3.
Experiments and analysis on analytic data are presented in
Session 4, and on discrete data are in Session 5. Conclusions
and further work are described at last in Session 6.
2. Related Work
Various algorithms to estimate curvature have been
proposed in literatures in recent years. They can be simply
classified as two categories: direct curvature fitting and
indirect curvature fitting though surface fitting. Two
approaches are selected as representatives of two types
ASIAGRAPH 2008 PROCEEDINGS
Curvature Estimation of 3D Point Cloud Surfaces Through the Fitting of Normal
Section Curvatures
Xiaopeng Zhang*
1
/LIAMA-NLPR, Institute of Automation, CAS; Hongjun Li
2
/LIAMA-NLPR, Institute of Automation, CAS; Zhanglin
Cheng
3
/LIAMA-NLPR, Institute of Automation, CAS
*
1
xpzhang@nlpr.ia.ac.cn,
2
hjli@nlpr.ia.ac.cn,
3
zhanglin.cheng@gmail.com