  Obstacle detection is a safety-critical problem in robot navigation, where
stereo matching is a popular vision-based approach. While deep neural networks
have shown impressive results in computer vision, most of the previous obstacle
detection works only leverage traditional stereo matching techniques to meet
the computational constraints for real-time feedback. This paper proposes a
computationally efficient method that employs a deep neural network to detect
occupancy from stereo images directly. Instead of learning the point cloud
correspondence from the stereo data, our approach extracts the compact obstacle
distribution based on volumetric representations. In addition, we prune the
computation of safety irrelevant spaces in a coarse-to-fine manner based on
octrees generated by the decoder. As a result, we achieve real-time performance
on the onboard computer (NVIDIA Jetson TX2). Our approach detects obstacles
accurately in the range of 32 meters and achieves better IoU (Intersection over
Union) and CD (Chamfer Distance) scores with only 2% of the computation cost of
the state-of-the-art stereo model. Furthermore, we validate our method's
robustness and real-world feasibility through autonomous navigation experiments
with a real robot. Hence, our work contributes toward closing the gap between
the stereo-based system in robot perception and state-of-the-art stereo models
in computer vision. To counter the scarcity of high-quality real-world indoor
stereo datasets, we collect a 1.36 hours stereo dataset with a mobile robot
which is used to fine-tune our model. The dataset, the code, and further
details including additional visualizations are available at
https://lhy.xyz/stereovoxelnet
