A point cloud is a set of data points defined in a given three-dimensional coordinates system.
Point clouds can be produced directly by 3D scanner which records a large number of points returned from the external surfaces of objects or earth surface. These data are exchanged between LiDAR users mainly through LAS format files (.las).
Airborne LiDAR systems also record point cloud, which density depends on:
- the laser specifications like the number of returns, the number of channels, the measurement range, the number of points returned per second, the Field Of View and the angular resolution, the rotation speed when concerned, …
- the distance from the scanned subject
- and the displacement speed in case of continuous mobile scanning performed from a vehicle, whether on an aerial platform, terrestrial vehicle or walking
Point cloud can also result from a photogrammectric reconstruction from pictures with a dedicated software. The points are then calculated by matching several photographs and camera positions and angles so as they correspond to pointsof the surface of the surveyed subject. The advantage of point cloud resulting from photogrammetry is that it is are already RGB colorized.
The density of such point cloud is dependent on:
- the quantity, overlap and quality of the photos
- the camera’s sensor size, resolution and focal length
- the Ground Sampling Distance (GSD) resulting from the camera specifications and the shooting protocol, which combines the displacement speed and the distance from the subject
- the photogrammetric reconstruction process parameters
Point clouds are used for many purposes, including to create 3D models for manufactured or hand-crafted parts and objects, for geomatic sciences and quality inspection, and for a multitude of visualization, animation, rendering and mass customization applications.
It is essential to understand that the point cloud is a set of individual, unrelated points with defined position, that need to be aligned, sometimes colorized and generally classified to be efficiently processed by a CAD or GIS sotfware for 3D modelling, DTM creation, vectorization, etc.