Note: The ASTM provides more in-depth discussion of several terms that have not been disclosed here; please refer to Designation E 2544-08b, “Standard Terminology for Three-Dimensional (3D) Imaging Systems” for more details.
3D Imaging System: A non-contact measurement instrument used to produce a 3D representation (for example, a a point cloud) of an object or site (ASTM).
3D Laser Scanning: the process of graphically capturing as-built physical elements of an object, facility or area and applying surveyed information to esch point. The process of collecting 3D coordinates of a given region of an object surface automatically and in a systematic pattern at a high rate (hundreds or thousands of points per second) achieving the results (i.e. 3D coordinates) in (near) real time.
Alignment: The process of aligning two objects in a common coordinate system. Commonly refers to aligning scan data.
As-built: Describes how a structure was actually constructed. The as-built condition of a structure may vary significantly from the design.
As-is: Describes the current status of the structure. The as-is condition of a structure may vary significantly from the as-built condition.
Azimuth: The angular distance measured along the horizon. Typically measured as an angular distance east from north.
Base station: In the context of external land surveying, a base station is a GPS receiver at an accurately know fixed location which is used to derive correction information for nearby portable GPS receivers. The correction data allows propogation and other effects to be corrected out of the position data obtained by the mobile stations, which proves greatly increased location precision and accuracy over the results obtained by uncorrected GPS receivers.
Benchmark: A point of reference for a measurement.
Calibration: A set of operations that establish, under specified conditions, the relationship between values of quantities indicated by a measuring system, or values represented by a material measure or a reference material, and the corresponding values realized by standards (ASTM).
Clash detection: Detecting possible collisions between as-is and proposed design.
Cross section: The intersection of a 3-dimensional body with a plane.
Dimensional control: A risk mitigation process that is applied to every project execution task that requires dimensional accuracy.
DEM (Digital Elevation Model): Digital stored xyz-triples of a surface. It is necessary to mention always which surface is meant by using the DEM ( for example DEM of the ground water surface, DEM of the earth’s surface).
DTM (Digital Terrain Model): Digital stored xyz-triples of the Earth’s surface. Therefore, the DTM is one special case of the DEM (DTM=DEM of the Earth’s surface).
Elevation: Angular distance measured from horizontal.
Error (of measurement): The result of measurement minus a true value of the measurand (the particular quantity subject to measurement (ASTM).
Field of View (FOV): The angular extent within which objects are measureable by a device such as an optical instrument without user interference. (1) For a scanner that is based on a spherical coordinate system, the FOV can typically be given by two angles; horizontal (azimuth) angle and vertical (elevation) angle (ASTM).
Fly-through: In virtual reality environments, fly through is movement of and object or model through a predefined path.
Georeferencing: Georeferencing is the process of aligning spatial data (layers that are shape files; polygons, points, etc.) to an image file such as a historical map, satellite image, or aerial photograph.
INS (Inertial Navigation System): A navigation system that uses a computer and motion sensors (accelerometers and gyroscopes) to continuously track the position, orientation, and velocity of an object without the need for external references.
Instrument origin: The point from which all instruments are referenced, that is, origin of the instrument coordinate reference frame (ASTM).
LiDAR (Light Detection and Ranging): A method of detecting distant objects and determining their position, velocity, or other characteristic by analysis of pulsed laser light refelected from their surfaces.
Mesh: A polygonal subdivision of the surface of a geometric model; also referred to as a polygonal model or triangulated model.
Meshing: The process of creating a 3D surface from point clouds.
Phase-Based: 3D laser scanners that produce measurements based on intensity modulated, continuous wave laser beams.
Photogrammetry: The process of taking precise measurements by using digital pictures and coded targets. For 3D scanning purposes, the coded targets and reference markers in the picture frame serve as references to align or register scan data.
Point cloud: Laser scan data from multiple scan stations in a defined volume space. [A] collection of data points in 3D space (frequently in the hundreds of thousands), for example as obtained using a 3D imaging system. (1) The distance between points is generalyy non-uniform and hence all three coordinates (Cartesian or spherical)
Point density: Number of points per unit. Usually the higher the point density is, the better representation of features.