Robotics
Point cloud
Definition
A point cloud is a collection of points representing sampled locations in space, usually with three-dimensional coordinates. Individual points may also carry attributes such as color or return intensity.
Also known as: Point clouds
Updated
Spatial samples from sensors
A depth camera or lidar can produce measurements that become points in a shared coordinate frame. Ouster's explanation describes this process for laser range measurements. The Point Cloud Library documentation describes point clouds as collections whose point type determines the stored data.
For a humanoid reaching toward a table, a cloud can represent the visible tabletop and objects on it. These samples can support geometric processing without already identifying which object is a cup or where it should be grasped.
Organized and unorganized clouds
An organized cloud preserves rows and columns, often corresponding to a depth image. An unorganized cloud is simply a collection of samples without that image arrangement. PCL documents both forms and explains why neighboring pixel relationships can make processing organized clouds more efficient.
A cloud is not a solid model
Points do not automatically define connected surfaces, occupied volumes, or object identities. Missing or invalid coordinates also need handling; PCL distinguishes clouds containing only finite data from those with invalid values. Converting a cloud into a mesh, an occupancy grid, or a distance field requires additional assumptions and processing.
Sources
Related terms
Lidar
Lidar measures distance using emitted laser light and its return from surfaces. Repeated range measurements across directions can form a spatial scan or three-dimensional point cloud.
Pose estimation
Pose estimation determines the position and orientation of an object or robot relative to a reference frame. For a rigid body in three-dimensional space, a full pose has three translational and three rotational degrees of freedom.
Signed distance field
A signed distance field represents a surface by assigning spatial locations a distance value whose sign distinguishes the two sides of the surface. Its zero level marks the surface, while the sign convention depends on the representation.