Centroid Distance Keypoint Detector for Colored Point Clouds Hanzhe Teng Dimitrios Chatziparaschis Xinyue Kan Amit K. Roy-Chowdhury Konstantinos Karydis University of California Riverside

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Centroid Distance Keypoint Detector for Colored Point Clouds
Hanzhe Teng, Dimitrios Chatziparaschis, Xinyue Kan, Amit K. Roy-Chowdhury, Konstantinos Karydis
University of California, Riverside
United States of America
{hteng007, dchat013, xkan001, amitrc, karydis}@ucr.edu *
Abstract
Keypoint detection serves as the basis for many com-
puter vision and robotics applications. Despite the fact that
colored point clouds can be readily obtained, most existing
keypoint detectors extract only geometry-salient keypoints,
which can impede the overall performance of systems that
intend to (or have the potential to) leverage color informa-
tion. To promote advances in such systems, we propose an
efficient multi-modal keypoint detector that can extract both
geometry-salient and color-salient keypoints in colored
point clouds. The proposed CEntroid Distance (CED) key-
point detector comprises an intuitive and effective saliency
measure, the centroid distance, that can be used in both 3D
space and color space, and a multi-modal non-maximum
suppression algorithm that can select keypoints with high
saliency in two or more modalities. The proposed saliency
measure leverages directly the distribution of points in a
local neighborhood and does not require normal estima-
tion or eigenvalue decomposition. We evaluate the pro-
posed method in terms of repeatability and computational
efficiency (i.e. running time) against state-of-the-art key-
point detectors on both synthetic and real-world datasets.
Results demonstrate that our proposed CED keypoint de-
tector requires minimal computational time while attaining
high repeatability. To showcase one of the potential ap-
plications of the proposed method, we further investigate
the task of colored point cloud registration. Results sug-
gest that our proposed CED detector outperforms state-of-
the-art handcrafted and learning-based keypoint detectors
in the evaluated scenes. The C++ implementation of the
proposed method is made publicly available at https://
github.com/UCR-Robotics/CED_Detector.
*We gratefully acknowledge the support of NSF grants #IIS-1724341
and #IIS-1901379, ONR grant #N00014-18-1-2252, and USDA/NIFA
#2021-67022-33453. Any opinions, findings, and conclusions or recom-
mendations expressed in this material are those of the authors and do not
necessarily reflect the views of the funding agencies.
1. Introduction
Keypoint detection serves as the basis across computer
vision and robotics applications such as 3D reconstruc-
tion [1,11], localization and mapping [8,12], and navigation
on point clouds [9, 17]. In such applications, colored point
clouds can be obtained from RGB-D cameras, where color
and depth images are aligned, or camera-LiDAR systems,
where they are collected after extrinsic calibration; this pro-
cess is often referred to as point cloud colorization or pho-
tometric reconstruction (e.g., [21]). However, most existing
keypoint detectors only consider geometric information and
fail to extract color-rich keypoints, which impedes the over-
all performance of systems that intend to (or have the poten-
tial to) leverage color information. Hence, there is need for
efficient keypoint detectors that can extract both geometric
and color information in the point cloud.
Keypoint detection aims to extract a subset of points
from the point cloud so that they can best represent the
original data in a compact form. Some successful key-
point detectors for 2D images, such as SIFT [19] and Har-
ris [10], have been extended to 3D space following the orig-
inal design ideas by the Point Cloud Library (PCL) com-
munity [28]. However, the data structures used in 2D im-
ages and 3D point clouds are fundamentally different. This
may limit deployment of such methods and has led to stud-
ies that focus on intrinsic properties of point clouds. Re-
cent advances in deep learning has helped introduce sev-
eral learning-based keypoint detectors and feature descrip-
tors [6, 18, 37, 39]. In spite of their strong performance
within their training domains, learned detectors and features
may not transfer over in new scenes that are different from
those used in training. For example, it may be challenging
for a system trained with data collected in indoor environ-
ments to operate in diverse outdoor scenes [2].
In contrast, methods that leverage the inherent properties
of point clouds may help overcome this difficulty. Several
existing methods focusing on geometric properties of point
clouds, such as NARF [29] and ISS [40], require eigenvalue
decomposition and/or normal estimation. These operations
are computationally expensive, especially when performing
arXiv:2210.01298v2 [cs.CV] 15 Jun 2023
keypoint detection at a large scale. In a distinct line of re-
search, it has been shown that incorporating color modality
can improve accuracy for applications such as point cloud
registration [23].
The main hypothesis underlying this work is that in-
corporating color modality (in addition to a geometric
modality) can help improve the overall performance, as the
amount of information passed on to the following compo-
nents in the system has increased. Despite existing descrip-
tors that can incorporate color information (e.g., [32]), to
the best of the authors’ knowledge there currently exists no
effective keypoint detector that can extract color-rich key-
points to feed to the descriptor. For instance, geometric-
based keypoint detectors can fail to extract keypoints on a
flat surface with color texture. While some methods (e.g.,
SIFT-3D) can extract color-rich keypoints, they do so at ex-
pense of losing geometric information (i.e. they can only
respond to one modality). This limitation can be linked to
lack of an effective non-maximum suppression algorithm to
combine the two modalities; this is one of the key contribu-
tions of this work.
To this end, we propose an efficient multi-modal key-
point detector, named CEntroid Distance (CED) keypoint
detector, that utilizes both geometric and photometric in-
formation. The proposed CED detector comprises an intu-
itive and effective saliency measure, the centroid distance,
that can be used in both 3D space and color space, and
a multi-modal non-maximum suppression algorithm that
can select keypoints with high saliency in two or more
modalities. The proposed saliency measure leverages di-
rectly the distribution of points in a local neighborhood and
does not require normal estimation or eigenvalue decom-
position. The proposed CED detector is evaluated in terms
of repeatability and computational efficiency (running time)
against state-of-the-art keypoint detectors on both synthetic
and real-world datasets. Results demonstrate that our pro-
posed CED keypoint detector requires minimal computa-
tional time while attaining high repeatability. In addition,
to showcase one of the potential applications of the pro-
posed method, we further investigate the task of colored
point cloud registration. Results show that our CED detec-
tor outperforms state-of-the-art crafted and learning-based
keypoint detectors in the evaluated scenes.
Contributions. The paper’s contributions are fourfold:
We propose an efficient multi-modal keypoint detector
that can extract both geometry-salient and color-salient
keypoints in a colored point cloud, with the potential to
be extended and applied to point clouds with multiple
modalities (e.g., colored by multi-spectrum images).
We propose to use an intuitive and effective measure
for keypoint saliency, the distance to centroid, which
can leverage directly the distribution of points and does
not require normal estimation or eigenvalue decompo-
sition.
We develop a multi-modal non-maximum suppression
algorithm that can select keypoints with high saliency
in two or more modalities.
We demonstrate through experiments in four datasets
that the proposed keypoint detector can outperform the
state-of-the-art handcrafted and learning-based key-
point detectors.
2. Related Work
3D keypoint detectors can be categorized as those ex-
tending designs originally developed for 2D images [10,19],
and those native to 3D point clouds [4, 20, 31, 40] and 3D
meshes [3, 34, 38]. Following the design in 2D images,
Harris family [10] computes covariance matrices of surface
normal or intensity gradient in 3D space, and in 3D and
color space (herein referred to as 6D space). SIFT [19]
applies the difference of Gaussian operator in scale-space
to find keypoints with local maximal response. However,
for 3D point clouds, the amount and position of points
within the spherical region are uncertain, making it hard
to obtain gradients. In 3D space, Normal Aligned Ra-
dial Feature (NARF) [29] measures saliency from surface
normal and distance changes between neighboring points.
Intrinsic Shape Signature (ISS) [40] and KeyPoint Qual-
ity (KPQ) [20] perform eigenvalue decomposition of the
scatter matrix of neighbor points and threshold on the ra-
tio between eigenvalues. Heat Kernel Signature (HKS) [31]
and Laplace-Beltrami Scale-space (LBSS) [34] measure the
saliency from the response to the Laplace-Beltrami opera-
tor in the neighborhood. Local Surface Patches (LSP) [4]
leverages local principal curvatures to construct the Shape
Index (SI) [7] as the measure of saliency. As in SIFT,
MeshDoG [38] and Salient Points (SP) [3] apply the
difference-of-Gaussian operator to construct the scale space
for saliency measure. We refer readers to the comprehen-
sive evaluation in [33] for more details.
In summary, the existing methods often apply an oper-
ator to obtain point normal, curvature and gradient in the
local region, and threshold on either a combination of the
obtained measures or the eigenvalues of the covariance ma-
trices. On the contrary, our proposed method leverages di-
rectly the point distribution and statistics in 3D space and
color space, without the need of normal estimation or eigen-
value decomposition.
Learning-based approaches, such as USIP [18] and
3DFeat-Net [37], have also been studied. 3DFeat-Net [37]
learns a 3D feature detector and descriptor for point cloud
matching using weak supervision, whereas USIP [18] trains
a feature proposal network with probabilistic Chamfer loss
in an unsupervised manner.
摘要:

CentroidDistanceKeypointDetectorforColoredPointCloudsHanzheTeng,DimitriosChatziparaschis,XinyueKan,AmitK.Roy-Chowdhury,KonstantinosKarydisUniversityofCalifornia,RiversideUnitedStatesofAmerica{hteng007,dchat013,xkan001,amitrc,karydis}@ucr.edu*AbstractKeypointdetectionservesasthebasisformanycom-puterv...

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