  In this paper, we present a factor-graph LiDAR-SLAM system which incorporates
a state-of-the-art deeply learned feature-based loop closure detector to enable
a legged robot to localize and map in industrial environments. These facilities
can be badly lit and comprised of indistinct metallic structures, thus our
system uses only LiDAR sensing and was developed to run on the quadruped
robot's navigation PC. Point clouds are accumulated using an inertial-kinematic
state estimator before being aligned using ICP registration. To close loops we
use a loop proposal mechanism which matches individual segments between clouds.
We trained a descriptor offline to match these segments. The efficiency of our
method comes from carefully designing the network architecture to minimize the
number of parameters such that this deep learning method can be deployed in
real-time using only the CPU of a legged robot, a major contribution of this
work. The set of odometry and loop closure factors are updated using pose graph
optimization. Finally we present an efficient risk alignment prediction method
which verifies the reliability of the registrations. Experimental results at an
industrial facility demonstrated the robustness and flexibility of our system,
including autonomous following paths derived from the SLAM map.
