Learning Compact Geometric Features
Marc Khoury
UC Berkeley
Qian-Yi Zhou
Intel Labs
Vladlen Koltun
Intel Labs
Abstract
We present an approach to learning features that rep-
resent the local geometry around a point in an unstruc-
tured point cloud. Such features play a central role in ge-
ometric registration, which supports diverse applications
in robotics and 3D vision. Current state-of-the-art local
features for unstructured point clouds have been manually
crafted and none combines the desirable properties of pre-
cision, compactness, and robustness. We show that features
with these properties can be learned from data, by optimiz-
ing deep networks that map high-dimensional histograms
into low-dimensional Euclidean spaces. The presented ap-
proach yields a family of features, parameterized by dimen-
sion, that are both more compact and more accurate than
existing descriptors.
1. Introduction
Local geometric descriptors represent the local geome-
try around a point in a point cloud. They play a central role
in geometric registration, which supports diverse applica-
tions in robotics and 3D vision [16] and underpins modern
3D reconstruction pipelines [42]. To enable accurate and
efficient registration, the descriptor must possess a number
of properties [12]. First, it should map the local geometry
to a vector in a Euclidean space R
n
; such Euclidean repre-
sentations support efficient geometric search structures and
nearest-neighbor queries. Second, the descriptor should be
discriminative: nearest neighbors in feature space should
correspond to points with genuinely similar local neighbor-
hoods. Third, the representation should be compact, with
a small dimensionality n: this supports fast spatial search.
Finally, the representation should be robust to artifacts that
are commonly encountered in real data, such as noise and
missing regions.
The design of local geometric descriptors has been the
subject of intensive study for the past two decades. Many
hand-crafted descriptors have been designed and evalu-
ated [19, 11, 25, 27]. Nevertheless, no existing descriptor
jointly satisfies the desiderata of high discriminative abil-
ity, compactness, and robustness [12]. Part of the challenge
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Dimensionality
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Precision (%)
CGF-12
CGF-32
CGF
FPFH
PFH
RoPS
SHOT
SI
USC
Figure 1. Our approach yields a family of Compact Geometric
Features (CGF), parameterized by dimension. This figure illus-
trates the performance of CGF on the SceneNN test set. Our fea-
tures are both more compact and more precise than the baselines.
The horizontal axis (dimensionality) is on a logarithmic scale.
is the difficulty of optimizing the parameters of a high-
dimensional feature representation by hand.
In this paper, we present an approach to learning local
geometric features from data. Our descriptor applies di-
rectly to unstructured point clouds and does not require a
clean and consistent surface parameterization [5], a vol-
umetric representation [41], or the synthesis of auxiliary
depth images [35]. Our features support nearest-neighbor
queries in a Euclidean space, which allows establishing
dense correspondences across point sets in near-linear time,
in contrast to the quadratic complexity required by pair-
wise matching networks. We thus obtain the first learned
geometric feature that can serve as a drop-in replace-
ment for state-of-the-art hand-crafted features in existing
pipelines [16, 42].
We show that the presented approach yields descrip-
tors that are both more discriminative and more compact
than state-of-the-art hand-crafted features. An illustration
is provided in Figure 1. Experiments demonstrate that our
Compact Geometric Features (CGF) yield more accurate
matches at lower query times. When CGF is used on the
standard Redwood benchmark for geometric registration,
with no training or fine-tuning on that dataset, it yields the
highest recall reported on the benchmark to date.
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arXiv:1709.05056v1 [cs.CV] 15 Sep 2017