Since radar point cloud has more noise, the ICP-based algo-
rithm is more likely to fall into a local optimum, resulting
in a larger motion estimation error. We have demonstrated
this experimentally at IV-C. Considering the importance of
map quality, our paper looks at how feature selection can be
used to optimize the process of map building and scan-to-
map matching in ICP-based radar SLAM, resulting in more
accurate maps and more robust state estimates.
In order to address these limitations, we propose a Map-
based Radar Odometry and Mapping system, MAROAM,
which is an accurate and robust map-based radar SLAM
framework based on LOAM [13]. In order to improve
map quality, we use a two-step geometry-probability fea-
ture selection strategy in the registration and map update
stage. In specificity, we first extract surface features by
calculating the Local Linearity and the Local Aggregation
with a geometry-based filter. We then involve a point-to-line
ICP method, using the surface features to solve the relative
pose transformation. Subsequently, we use a probability-
based filter to dynamically filter out the features that are
not frequently selected in the ICP matching process. Using
the more frequent features, our algorithm realizes the scan-
to-map matching strategy of ICP-based radar SLAM for the
first time. Additionally, We use the Scan Context [14] for
loop closure and modify it to fit the radar data format.
We evaluate the performance of MAROAM on the three
datasets: the Oxford Radar RobotCar Dataset [7], the Mul-
Ran Dataset [15] and the Boreas Dataset [16]. We consider
a variety of experimental settings with different scenery,
weather, and road conditions. The experimental results show
that the accuracy of MAROAM is 7.95%, 37.0% and 8.9%
higher than the currently best-performing algorithms on these
three datasets, respectively. The ablation results also show
that our map-based odometry performs 28.6% better than
the commonly used scan-to-frames method.
In summary, our main contributions are as follows:
•We propose MAROAM, an map-based radar SLAM
framework based on LOAM. Using a geometry-
probability two-step feature selection, our algorithm
realizes the scan-to-map matching strategy of ICP-based
radar SALM for the first time.
•We evaluate our MAROAM on three datasets which
contain a variety of scenarios, weathers, and road condi-
tions. Experiments show that our algorithm outperforms
SOTA algorithm on all three datasets.
II. RELATED WORKS
A. Radar SLAM
We divide the existing radar odometry/SLAM algorithms
into four categories according to the method of estimating
the relative pose:
1) Direct methods: Checchin et al. [17] first time use the
Fourier-Mellin Transform (FMT) to register radar images in
a sequence for motion estimation. PhaRao [18] apply FMT
to Cartesian and log polar radar images to estimate rotation
and translation to decouple rotation and translation.
2) ICP-based methods: Adolfsson et al. [10] process the
landmarks extracted by CFAR through k-strongest filtering
in Cartesian coordinates, and optimizes the point-to-line
optimize metric to estimate the relative pose. Kung et al.
[19] propose a RO with probabilistic submap building, and
an NDT-based radar scan matching. Both of them use scan-
to-submap matching, but the submaps they use are only the
superposition of multiple frames, and there is no mapping
process.
3) Descriptor-based methods: Considering the unneces-
sary influence of radar echo, Cen et al. [2] propose an
algorithm to extract landmarks, and performe scan match-
ing by greedily adding features correspondence based on
unary descriptor and pairwise compatibility score. After
that, another feature extraction algorithm that only use one
parameter is proposed by Cen et al. [3], and graph matching
is used for scan matching. Hone et al. [20], [21] propose
a full radar-based SLAM pipeline, RadarSLAM, composed
of pose tracking, local mapping, loop closure detection and
pose graph optimization. RadarSLAM uses visual features
for scan matching and M2DP [22] descriptor based on point
cloud for loop detection.
4) Learning-based methods: Barnes et al. [5] use deep
neural network to learn an embedding space that is basically
free of artifacts and interference, which is used to perform ef-
fective correlation matching between continuous radar scans,
and achieve high accuracy without considering spatial cross-
validation(CSV). A self supervised learning framework is
proposed by Barnes et al. [4] to detect the robust key features
of range estimation and metric positioning in radar. Burnett et
al. [23] uses unsupervised method to extract features, which
increases generalization and performs well on both Oxford
and Boreas.
B. LiDAR SLAM
LOAM [13] is the pioneering work of 3D LiDAR SLAM,
which proposes a basic framework. LOAM extracts edge
features and plane features from the original point cloud,
and designs related loss functions for each type of feature.
The matching consists of a fast frame-to-frame match and a
slow frame-to-graph match. F-LOAM [24] follows LOAM
and abandons the scan-to-scan match and replaces it by
only scan-to-map with high frequency. Duan et al. [25]
propose a feature filter, pFilter, by properly measuring each
feature point’s p-Index and only keeping those with high
index values, and improved both the efficiency and accuracy
of the registration process. Our work is inspired by the
aforementioned LiDAR SLAM.
III. METHOD
A. System Overview
An overview of MAROAM is shown in Fig. 2. The system
receives input from a 2D radar image and outputs a 3-
DOF pose estimation and a global consistent map. The
SLAM system consists of two modules: tracking and loop
closure. The tracking module is used for feature extraction,
feature filtering and real-time motion estimation, and the