Architecture and Process Flow¶
The topmost object in LSD-SLAM is lsd_slam::SlamSystem. It is the
primary container of both system state and the sub-threads which do the work.
Once created, the main access point is lsd_slam::SlamSystem::nextImage()
(for mono) and lsd_slam::SlamSystem::nextImageSet() (for stereo)
which are used to provide the next image to the algorithm.
The main data structures are:
lsd_slam::Frame- is a single image from the incoming data stream. It contains pre-computed values (for example, an image pyramid, gradient image, etc.) used when processing that image. Frames are generally not retained, unless an image is converted to a KeyFrame
lsd_slam::KeyFrame- represents a single key frame. It contains the original Frame, along with supplemental data structures used to perform KeyFrame-specific functions: a DepthMap for the associated point cloud, and a TrackingReference for accelerating subsequent tracking operations against the Key Frame.
lsd_slam::DepthMap- contains the data and code for performing KeyFrame point cloud updates (virtual baseline stereo).
lsd_slam::KeyFrameGraph- stores all KeyFrames both as a simple list and as an undirected pose graph.
LSD-SLAM has four top-level threads. The thread objects are designed as execution contexts first, although they also store the subset of the “global” state which is most relevant to their mission.
lsd_slam::TrackingThread- is responsible for calculating the pose of the current image relative to the current Keyframe.
lsd_slam::MappingThread- takes tracked frames and uses them to update the depth map estimate for the current KeyFrame.
lsd_slam::ConstraintSearchThread- operates in spare cycles to search for additional cross-links between KeyFrames based on appearance.
lsd_slam::OptimizationThread- operates in spare cycles to globally optimize the pose graph.
Each thread object is implemented as an (ActiveObject)[https://github.com/apl-ocean-engineering/libactiveobject], a work queue model where method calls to the object are executed asynchronously in a separate thread of execution.
