Indoor Environment Mapping Tutorials

OctoMap and RTAB-Map

• Octree
  • An octree is a tree data structure in which each internal node has exactly eight children.
  • Octrees are most often used to partition a three-dimensional space by recursively subdividing it into eight octants

images/octree.png

Left: Recursive subdivision of a cube into octants. Right: The corresponding octree.

• OctoMap

  • The OctoMap library implements a 3D occupancy grid mapping approach, providing data structures and mapping algorithms in C++ particularly suited for robotics
  • The map implementation is based on an Octree and is designed to meet the following requirements:
    1. Full 3D model - The map is able to model arbitrary environments without prior assumptions about it
    2. Updatable - It is possible to add new information or sensor readings at any time.
    3. Flexible - The extent of the map does not have to be known in advance.
    4. Compact - The map is stored efficiently, both in memory and on disk

• RTAB-Map

  • Simultaneous Localisation And Mapping (SLAM) is the computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of an agent's location within it
  • RTAB-Map (Real-Time Appearance-Based Mapping) is a RGB-D Graph-Based SLAM approach based on an incremental appearance-based loop closure detector
  • RTAB-Map can be used alone with a hand-held Kinect or stereo camera for 6DoF RGB-D mapping

• Localisation and Loop closure detection

  • Loop closure is the problem of recognising a previously-visited location and updating the map accordingly.
  • The loop closure detector in RTAB-Map uses a bag-of-words approach to determinate how likely a new image comes from a previous location or a new location
  • The visual features used by RTAB-Map can be computed using a number of popular techniques from computer vision including SIFT, SURF, BRIEF, FAST, etc

images/RTAB-Map-features.png

• OctoMap Vs RTAB-Map

  • OctoMap is only a mapping approach. It is an efficient way of storing and manipulating 3D maps
  • RTAB-Map is a complete SLAM approach. It does localisation based on visual features it detects in the RGB video stream
  • For mapping, OctoMap requires a backend SLAM package for localisation and loop closure detection while it is possible to do mapping with just RTAB-Map

• References

  • http://octomap.github.io
  • http://introlab.github.io/rtabmap/
  • https://en.wikipedia.org/wiki/Octree
  • https://en.wikipedia.org/wiki/Simultaneous_localization_and_mapping
  • http://www.pirobot.org/wordpress/rtab-map-saves-the-kidnapped-robot/