Point cloud

Encyclopedia

A

Point clouds are most often created by 3D scanner

s. These devices measure in an automatic way a large number of points on the surface of an object, and often output a point cloud as a data file. The point cloud represents the set of points that the device has measured.

As the result of a 3D scanning process 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.

While point clouds can be directly rendered and inspected, usually point clouds themselves are generally not directly usable in most 3D applications, and therefore are usually converted to polygon

or triangle mesh

models, NURBS surface models, or CAD models through a process commonly referred to as surface reconstruction.

There are many techniques for converting a point cloud to a 3D surface. Some approaches, like Delaunay triangulation

, alpha shape

s, and ball pivoting, build a network of triangles over the existing vertices of the point cloud, while other approaches convert the point cloud into a volumetric

distance field and reconstruct the implicit surface so defined through a marching cubes

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.

In geographic information system

, point clouds are one of the sources to make digital elevation model

of the terrain. The point clouds are also employed in order to generate 3D model of urban environment, e.g.

**point cloud**is a set of vertices in a three-dimensional coordinate system. These vertices are usually defined by*X*,*Y*, and*Z*coordinates, and typically are intended to be representative of the external surface of an object.Point clouds are most often created by 3D scanner

3D scanner

A 3D scanner is a device that analyzes a real-world object or environment to collect data on its shape and possibly its appearance . The collected data can then be used to construct digital, three dimensional models....

s. These devices measure in an automatic way a large number of points on the surface of an object, and often output a point cloud as a data file. The point cloud represents the set of points that the device has measured.

As the result of a 3D scanning process point clouds are used for many purposes, including to create 3D CAD

Computer-aided design

Computer-aided design , also known as computer-aided design and drafting , is the use of computer technology for the process of design and design-documentation. Computer Aided Drafting describes the process of drafting with a computer...

models for manufactured parts, metrology

Metrology

Metrology is the science of measurement. Metrology includes all theoretical and practical aspects of measurement. The word comes from Greek μέτρον , "measure" + "λόγος" , amongst others meaning "speech, oration, discourse, quote, study, calculation, reason"...

/quality inspection, and a multitude of visualization, animation, rendering and mass customization

Mass customization

Mass customization, in marketing, manufacturing, call centres and management, is the use of flexible computer-aided manufacturing systems to produce custom output...

applications.

While point clouds can be directly rendered and inspected, usually point clouds themselves are generally not directly usable in most 3D applications, and therefore are usually converted to polygon

Polygon mesh

A polygon mesh or unstructured grid is a collection of vertices, edges and faces that defines the shape of a polyhedral object in 3D computer graphics and solid modeling...

or triangle mesh

Triangle mesh

A triangle mesh is a type of polygon mesh in computer graphics. It comprises a set of triangles that are connected by their common edges or corners....

models, NURBS surface models, or CAD models through a process commonly referred to as surface reconstruction.

There are many techniques for converting a point cloud to a 3D surface. Some approaches, like Delaunay triangulation

Delaunay triangulation

In mathematics and computational geometry, a Delaunay triangulation for a set P of points in a plane is a triangulation DT such that no point in P is inside the circumcircle of any triangle in DT. Delaunay triangulations maximize the minimum angle of all the angles of the triangles in the...

, alpha shape

Alpha shape

In computational geometry, an alpha shape, or α-shape, is a family of piecewise linear simple curves in the Euclidean plane associated with the shape of a finite set of points. They were first defined by . The alpha-shape associated with a set of points is a generalization of the concept of the...

s, and ball pivoting, build a network of triangles over the existing vertices of the point cloud, while other approaches convert the point cloud into a volumetric

Voxel

A voxel is a volume element, representing a value on a regular grid in three dimensional space. This is analogous to a pixel, which represents 2D image data in a bitmap...

distance field and reconstruct the implicit surface so defined through a marching cubes

Marching cubes

Marching cubes is a computer graphics algorithm, published in the 1987 SIGGRAPH proceedings by Lorensen and Cline, for extracting a polygonal mesh of an isosurface from a three-dimensional scalar field...

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

Medical imaging

Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...

. Using point clouds multi-sampling and data compression

Data compression

In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....

is achieved.

In geographic information system

Geographic Information System

A geographic information system, geographical information science, or geospatial information studies is a system designed to capture, store, manipulate, analyze, manage, and present all types of geographically referenced data...

, point clouds are one of the sources to make digital elevation model

Digital elevation model

A digital elevation model is a digital model or 3-D representation of a terrain's surface — commonly for a planet , moon, or asteroid — created from terrain elevation data....

of the terrain. The point clouds are also employed in order to generate 3D model of urban environment, e.g.

## See also

- MeshLabMeshLabMeshLab, is a free 3D mesh processing software program; MeshLab, started in late 2005, is an open-source general-purpose system aimed to help the processing of the typical not-so-small unstructured 3D models that arise in the pipeline of processing of the data coming from 3D scanning...

, an open source tool for managing point clouds and converting them into 3D triangular meshes; - PCL (Point Cloud Library)PCL (Point Cloud Library)PCL is a standalone open-source framework for n-dimensional point clouds and 3D geometry processing. The library contains algorithms for filtering, feature estimation, surface reconstruction, registration, model fitting, and segmentation. PCL is developed by a large consortium of researchers and...

, a comprehensive BSD open source library for n-D Point Clouds and 3D geometry processing

## External links

- PCL (Point Cloud Library) – a comprehensive BSD open source library for n-D Point Clouds and 3D geometry processing. http://pointclouds.org