# Point cloud

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Point cloud

A point cloud is a set of vertices in a three-dimensional coordinate system. These vertices are usually defined by "X", "Y" and "Z" coordinates.

Point clouds are most often created by 3D scanners. These devices measure a large number of points on the surface of an object, and output a point cloud as a data file. The point cloud represents the visible surface of the object that has been scanned or digitized.

Point clouds are used for many purposes, including to create 3D CAD models for manufactured parts, metrology/quality inspection, and a multitude of visualization, animation, rendering and mass customization applications.

Point clouds themselves are generally not directly usable in most 3D applications, and therefore are usually converted to triangle mesh models, NURBS surface models, or CAD models through a process commonly referred to as reverse engineering so that they can be used for various purposes.
Techniques for converting a point cloud to a polygon mesh include Delaunay triangulation and more recent techniques such as Marching triangles and the Ball-Pivoting algorithm.

One application in which point clouds are directly usable is industrial metrology or inspection. The point cloud of a manufactured part can be aligned to a CAD model (or even another point cloud), and compared to check for differences. These differences can be displayed as color maps that give a visual indicator of the deviation between the manufactured part and the CAD model. Geometric dimensions and tolerances can also be extracted directly from the point cloud.

Point clouds can also be used to represent volumetric data used for example in medical imaging. Using point clouds multi-sampling and data compression is achieved [Sitek et al. "Tomographic Reconstruction Using an Adaptive Tetrahedral Mesh Defined by a Point Cloud" "IEEE Trans. Med. Imag." 25 1172 (2006)] .

References

ee also

MeshLab An open source tool that can convert point clouds to a triangle mesh using the OFF file format.

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