PhD Defence • 3D Computer Vision • LiDAR-based 3D Perception from Multi-frame Point Clouds for Autonomous Driving

Please note: This PhD defence will take place online.

Chengjie Huang, PhD candidate
David R. Cheriton School of Computer Science

Supervisor: Professor Krzysztof Czarnecki

3D perception is a critical component of autonomous driving systems, where accurately detecting objects and understanding the surrounding environment is essential for safety.  Recent advances in Light Detection and Ranging (LiDAR) technology and deep neural network architectures have enabled state-of-the-art (SOTA) methods to achieve high performance in 3D object detection and segmentation tasks. Many approaches leverage the sequential nature of LiDAR data by aggregating multiple consecutive scans to generate dense multi-frame point clouds. However, the challenges and applications of multi-frame point clouds have not been fully explored.

This thesis makes three key contributions to advance the understanding and application of multi-frame point clouds in 3D perception tasks.

First, we address the limitations of multi-frame point clouds in 3D object detection. Specifically, we observe that increasing the number of aggregated frames has diminishing returns and even performance degradation, due to objects responding differently to the number of aggregated frames. To overcome this performance trade-off, we propose an efficient adaptive method termed Variable Aggregation Detection (VADet). Instead of aggregating the entire scene using a fixed number of frames, VADet performs aggregation per object, with the number of frames determined by an object's observed properties, such as speed and point density. This adaptive approach reduces the inherent trade-offs of fixed aggregation, improving detection accuracy.

Next, we tackle the challenge of applying multi-frame point cloud to 3D semantic segmentation. Point-wise prediction on dense multi-frame point clouds can be computationally expensive, especially for SOTA transformer-based architectures. To address this issue, we propose MFSeg, an efficient multi-frame 3D semantic segmentation framework. MFSeg aggregates point cloud sequences at the feature level and regularizes the feature extraction and aggregation process to reduce computational overhead without compromising accuracy. Additionally, by employing a lightweight MLP-based point decoder, MFSeg eliminates the need to upsample redundant points from past frames, further improving efficiency.

Finally, we explore the use of multi-frame point clouds for cross-sensor domain adaptation. Based on the observation that multi-frame point clouds can weaken the distinct LiDAR scan patterns for stationary objects, we propose Stationary Object Aggregation Pseudo-labelling (SOAP) to generate high quality pseudo-labels for 3D object detection in a target domain. In contrast to the current SOTA in-domain practice of aggregating few input frames, SOAP utilizes entire sequences of point clouds to effectively reduce the sensor domain gap.

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