  Lidar has become an essential sensor for autonomous driving as it provides
reliable depth estimation. Lidar is also the primary sensor used in building 3D
maps which can be used even in the case of low-cost systems which do not use
Lidar. Computation on Lidar point clouds is intensive as it requires processing
of millions of points per second. Additionally there are many subsequent tasks
such as clustering, detection, tracking and classification which makes
real-time execution challenging. In this paper, we discuss real-time dynamic
object detection algorithms which leverages previously mapped Lidar point
clouds to reduce processing. The prior 3D maps provide a static background
model and we formulate dynamic object detection as a background subtraction
problem. Computation and modeling challenges in the mapping and online
execution pipeline are described. We propose a rejection cascade architecture
to subtract road regions and other 3D regions separately. We implemented an
initial version of our proposed algorithm and evaluated the accuracy on CARLA
simulator.
