September 2019 Full - page 633

Enhanced 3D Mapping with an RGB-D Sensor
via Integration of Depth Measurements
and Image Sequences
Bo Wu, Xuming Ge, Linfu Xie, and Wu Chen
Abstract
State-of-the-art visual simultaneous localization and mapping
(SLAM) techniques greatly facilitate three-dimensional (3D)
mapping and modeling with the use of low-cost red-green-
blue-depth (RGB-D ) sensors. However, the effective range of
such sensors is limited due to the working range of the infra-
red (IR) camera, which provides depth information, and thus
the practicability of such sensors in3D mapping and model-
ing is limited. To address this limitation, we present a novel
solution for enhanced 3D mapping using a low-cost RGB-D
sensor. We carry out state-of-the-art visual SLAM to obtain 3D
point clouds within the mapping range of the RGB-D sensor
and implement an improved structure-from-motion (SfM) on
the collected RGB image sequences with additional constraints
from the depth information to produce image-based 3D point
clouds. We then develop a feature-based scale-adaptive reg-
istration to merge the gained point clouds to further generate
enhanced and extended 3D mapping results. We use two chal-
lenging test sites to examine the proposed method. At these
two sites, the coverage of both generated 3D models increases
by more than 50% with the proposed solution. Moreover, the
proposed solution achieves a geometric accuracy of about
1% in a measurement range of about 20 m. These positive
experimental results not only demonstrate the feasibility and
practicality of the proposed solution but also its potential.
Introduction
Red-green-blue-depth (RGB-D) sensors (such as the Kinect or
the Structure sensors) have remarkable advantages, such as
mobility and low cost, and have been used extensively in
three-dimensional (3D) mapping and visual simultaneous
localization and mapping (SLAM) (Dryanovski et al. 2013). An
RGB-D sensor captures RGB images by a RGB camera and pixel-
wise depth information by an infrared (IR) camera together
with an IR projector, and it can thus produce textured 3D
point clouds in the object coordinate system via transforma-
tion from the RGB camera coordinate system to the IR camera
coordinate system (Tang et al. 2016). RGB-D sensors have thus
been used for 3D mapping and modeling both in indoor and
outdoor environments in recent years (Henry et al. 2010; Kerl
et al. 2013; Tang et al. 2016). Although RGB-D sensors can be
used to build 3D models of unprecedented richness, they
have drawbacks that limit their application in practice: they
measure depth only up to a limited distance (typically less
than 5 m), and the gained depth values are much noisier than
those provided by traditional laser scanners. Moreover, the
field of view of a depth camera is far more constrained than
that of traditional laser scanners that are typically used for 3D
mapping and modeling.
The above-mentioned drawbacks of RGB-D sensors narrow
the scope of their application in 3D mapping and modeling
(Ye and Wu 2018). For example, when it is impossible to get
close enough to scan targets in the working environment, an
RGB-D sensor cannot provide desirable results. Other solutions
are therefore needed to improve the feasibility and practical-
ity of such sensors. This paper introduces the structure-from-
motion (SfM) and multiviewstereo ( MVS) methods to generate
extended 3D models in relatively distant ranges using RGB
image sequences to supplement the 3D models obtained from
the RGB-D sensors at short range. The proposed solution has
three main advantages. (1) It requires no additional effort;
although the SfM and MVS are offline productions, the RGB
image sequences can be simultaneously collected with the
online SLAM. (2) It provides improved SfM constrained by the
additional depth information. (3) It uses scale-adaptive regis-
tration to fuse the multisensor point clouds.
The remainder of this paper is organized as follows. In the
section “Related Work”, the paper briefly introduces works
related to the RGB-D SLAM and SfM. In the section “Enhanced
3D Mapping by Integrating Depth Measurements and Image
Sequences”, the proposed solution for enhanced 3D mapping
is described in detail. In the “Experimental Evaluation” sec-
tion, two challenging cases are tested to demonstrate the posi-
tive properties of the proposed system. In the final section,
concluding remarks are presented.
Related Work
The advent of RGB-D sensors has led to a great deal of progress
in SLAM. Typically, a visual SLAM system consists of a camera-
tracking frontend that uses visual odometry (Engel et al. 2014;
Kerl et al. 2013) and a backend that generates and maintains
a map of key-frames and reduce global drift via loop closure
detection and map optimization (Mur-Artal and Tardós 2017;
Gao et al. 2018). Most state-of-the-art methods estimate six
degrees of freedom between adjacent frames based on the
sparsely selected visual features to represent the camera
motion (Liu et al. 2018). The two main classical approaches
are to minimize the photometric error between consecu-
tive stereo pairs (Comport et al. 2007) and to minimize the
geometric error between 3D points (e.g., the iterative closest
point [ICP] (Besl and McKay 1992) and the three-dimensional
normal-distributions transform (Magnusson 2009). Tykkälä et
al. (2011) and Whelan et al. (2013) used the minimization of
photometric and geometric error to estimate camera motion.
Newcombe et al. (2011) proposed an incremental strategy to
register RGB-D frames. In recent years, visual-inertial SLAM
has been increasingly used (Hesch et al. 2014) and these
The Hong Kong Polytechnic University, Department of Land
Surveying & Geo-Informatics ( xuming.ge@polyu.edu.hk).
Photogrammetric Engineering & Remote Sensing
Vol. 85, No. 9, September 2019, pp. 633–642.
0099-1112/19/633–642
© 2019 American Society for Photogrammetry
and Remote Sensing
doi: 10.14358/PERS.85.9.633
PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING September 2019 633