VERIFY 3D LIBRARY
VERIFY 3D GLOSSARY
3D MEASUREMENT
A measurement that includes three values, one each for the X, Y, and Z directions. The values are the distances from an arbitrary 0,0,0 point.
​ACCURACY
How close a measurement comes to a specific value. In different disciplines accuracy is defined in different terms. In laser scanning, generally it means how close to the true value a measurement comes. cf. PRECISION
ACCURACY – MEASURED & ACCURACY - REPRESENTED
Measured accuracy refers to the accuracy of the direct laser measurements taken while scanning. Measured accuracy refers to the POINT CLOUD. Represented accuracy refers to the accuracy of the objects in the CAD model. Objects are sometimes drawn square, plumb, and true even though they are not. The choice of representing objects as square, plumb, and true or not depends on the objectives of scanning and modeling.
AS BUILT & AS DESIGNED
Any complex structure, such as a hospital, is carefully designed, but as construction proceeds, changes are made, sometimes intentionally, sometimes not. Laser scanning is often used to compare the design drawings or models to the actual construction. The differences between AS BUILT and AS DESIGNED are useful to owners, constructors, regulatory agencies, and others.
BENCHMARK
A surveyor’s term for a precisely known elevation at a specific coordinate.
BÉZIER CURVE
A mathematical representation of a parametric curved line. This allows the succinct representation of complex curves that do not conform to simple geometric shapes such as circles, rectangles, and ellipses that are easily defines by simple equations. Beyond the BÉZIER CURVE is the Bézier surface for representing three dimensional curves.
BIM
An abbreviation for Building Information Modeling. A set of methods for creating a virtual duplicate of the physical and functional characteristics of a structure according to certain rules, conventions, and standards.
CAD MODEL
Short for Computer Aided Design Model. CAD models are data representations of a (generally) physical thing. The data can be stored in many different formats, most of which are propriety to the vendor of the CAD system. CAD models can be built manually or built from POINT CLOUDs. The construction of the CAD MODEL from the POINT CLOUD is semi-automatic.
CAD SYSTEM
A collection of software that is used to manipulate CAD MODELS and POINT CLOUDS. Among the many companies that offer such are AutoDesk, Bentley, Dassault Systèmes, Technodigit SARL. Among the many products for such are AutoCAD, Revit, Navisworks, Microstation, 3D Solidworks, 3D Reshaper.
CONTROL POINT
A laser scanning term for a location with precisely known coordinates. During scanning, control points are often established at locations that will not move, such as the base of a structural steel column.
DENSITY OF SCAN
The number of measurements taken by the laser scanner per unit area. For example, if the laser scanner is set to take twenty measurements per square meter of a surface, that is one-fifth the density of one-hundred measurements per square meter. Specifications for laser scanning should include density of scan, and this is usually written as the number of measurements per unit area at a specified distance from the scanner. Specifications for laser scanning change depending on the purposes to which the scanning data will be put. Collecting measurements more dense than needed wastes time. Collecting measurements less dense than needed runs the risk of insufficient ACCURACY in the resulting models and drawings.
LASER SCANNER
A surveying instrument that emits pulses of laser light and calculates distances based on differences between the emitted pulse and the light that was reflected back from some object.
LEVEL OF DEVELOPMENT (LOD)
A measurement of the amount of detail in a modeled object. The Level of Development is usually expressed as a number between 100 and 500; the higher the number, the more detail. Modeling to a higher level of development is more time-consuming and expensive than modeling to a lower level. Specifications for laser scanning and modeling should take into account the uses to which the data will be put and identify a specific Level of Development that matches the needs of those who will use the data.
MEP
An abbreviation for Mechanical Electrical Plumbing, which distinguishes those systems from the architectural, structural, HVAC, and other components of a building.
MESH or WIRE MESH
A data format built from the POINT CLOUD in which each measured point is connected to its nearest neighbors in a 3-dimensional surface of triangles. The MESH is used for various purposes including analysis of variations in a surface.
PHASE DIFFERENCE
One of the ways a LASER SCANNER measures the distance from the scanner to an object. In this method, the circuitry of the LASER SCANNER compares the phase of the light reflected from the object to the phase of the light emitted by the scanner. From this difference, the scanner can calculate the distance to the object. cf. TIME OF FLIGHT
POINT CLOUD
The collection of measurements obtained from laser scanning. Each measurement consists of X, Y, & Z coordinates and the albedo or reflectivity of the surface. When many measured points are displayed on a computer screen, the resulting image of the object(s) appears cloud like, similar to a pointillist painting of the late 19th. century.
PRECISION
How closely a set of measurements come to each other, or how closely they are spaced. cf. ACCURACY. For example, if the distance to an object is measured four times (1003 mm, 1002 mm, 1004 mm, 1005 mm) the measurements are more precise than another set (1010 mm, 998 mm, 1001 mm, 1005 mm) even though the two sets have the same average value. And all the measurements could be inaccurate or accurate. PRECISION can be represented as the standard deviation of a set of measurements.
REALITY CAPTURE
Another name for the process of laser scanning. The scanning data in the form of the POINT CLOUD is a fully measured, virtual duplicate of the objects or space that was scanned.
REGISTRATION
Combining multiple scan positions into a single conglomerate POINT CLOUD. Scans are mathematically aligned using millions of overlapping points between stations. Methods include scan-to-scan and scan to target registration. Targets may be placed on survey control points allowing registration to global or site survey coordinates.
TARGET
An object of known dimensions and characteristics placed in an area before scanning begins. Placing targets in the scanned area assists in the accurate REGISTRATION of scans, and targets improve the overall ACCURACY of the scanning data.
TIME OF FLIGHT (TOF)
One of the ways a LASER SCANNER measures the distance from the scanner to an object. In this method, the circuitry of the scanner multiplies the time that light took to travel to the object and back by the speed of light in the ambient air divided by two. Variations in the density of the air can affect the speed of light and consequently the measurements. cf. PHASE DIFFERENCE.
USIBD
An abbreviation for United States Institute of Building Documentation, an organization devoted to the development of conventions and standards for collecting and organizing the various documents of building design, construction, and maintenance.
