Learning-AI

Visual SLAM for Automated Driving: Exploring the Applications of Deep Learning

December 2020

tl;dr: An overview of deep learning application in SLAM for autonomous driving.

Overall impression

The paper provides a good overview of VSLAM applications in autonomous driving.

Key ideas

• Three main scenarios for autonomous driving: highway, parking lot and city
  • Parking: needs an accurate environment map in the near vicinity of the car while driving at low speed.
  • Highway: 20 FPS or more.
    • Orb-SLAM is doing a great job already in highway scenes.
  • City: Many dynamic objects that needs to be detected actively or passively during 3D reconstruction.
    • Orb-SLAM performs poorly. The ability to reconstruct static points with stability against lots of dynamic objects within the scene is key.
• Two approaches to autonomous driving
  • Mediated perception approach
  • End-to-end approach. Perception can be used as auxiliary supervision.
• Two main types of HD map
  • Dense semantic point cloud maps
    • TomTom, Google
    • Mapped with lidar/camera
    • Provides strong prior to semantic segmentation
  • Semantic landmarks maps
    • MobileEye, HERE
    • Mapped with camera
• Private small scale map
  • Small scale mapping capability is necessary
  • Privacy, Coverage and dynamic
• Fundamental pipelines of SLAM
  • Tracking (Visual Odometry, frontend)
  • Mapping: sparse (feature based method) or dense (direct method)
  • Global optimization and loop closure
  • Re-localization
• History of SLAM
  • Feature based SLAM
    • MonoSLAM: EKF-tracking
    • PTAM: bundle adjustment
    • Orb-SLAM: loop closure + global pose optimization
  • Direct SLAM
    • DTAM: photometric error
    • LSD-SLAM: loop closure + global pose optimization
    • DSO: geometric error, lens distortion, exposure time calib
• Deep learning opportunities in SLAM
  • depth estimation
  • optical flow
  • feature correspondence
  • bundle adjustment
  • semantic segmentation
  • camera pose estimation

Technical details

• Stereo SLAM are acceptable for autonomous driving applications, but monocular results are weak and unacceptable.
• Rolling shutter has to be accounted for on highways for accurate SLAM
• There is still no mature solutions for how to do self-repairing map, and map on the vehicle.
• We need motion segmentation for general obstacle detection.

Notes

• Do we really need 20 FPS for parking lot and city?