- 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 customizationapplications.
Point clouds themselves are generally not directly usable in most 3D applications, and therefore are usually converted to
triangle meshmodels, NURBS surface models, or CAD models through a process commonly referred to as reverse engineeringso that they can be used for various purposes.
Techniques for converting a point cloud to a
polygon meshinclude Delaunay triangulationand more recent techniques such as Marching trianglesand 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 compressionis achieved [Sitek et al. "Tomographic Reconstruction Using an Adaptive Tetrahedral Mesh Defined by a Point Cloud" "IEEE Trans. Med. Imag." 25 1172 (2006)] .
MeshLabAn open source tool that can convert point clouds to a triangle mesh using the OFF file format.
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