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Glossary

Glossary of Terms


AB CD • E • F • GH • I • J • K • L • M • N • OP • Q • R • S • T • U • V • W • X • Y • Z

 

AERIAL PHOTOGRAPHY

Is the taking of photographs of the ground from an elevated position. Usually the camera is not supported by a ground-based structure. Platforms for aerial photography include fixed-wing aircraft, helicopters, multirotor Unmanned Aircraft Systems (UAS), balloons, blimps and dirigibles, rockets, pigeons, kites, parachutes, stand-alone telescoping and vehicle-mounted poles. Mounted cameras may be triggered remotely or automatically; hand-held photographs may be taken by a photographer.


https://en.wikipedia.org/wiki/Aerial_photography

 

BARE EARTH MODEL

A digital terrain surface without vegetation or structures.  It can be in the form of a point-cloud, a DEM grid or a TIN.

BREAKLINE

A linear feature that describes a change in the smoothness or continuity of a surface. The two most common forms of breaklines are as follows:

  • A soft (round) breakline ensures that known z values along a linear feature are maintained (for example, elevations along a pipeline, road centerline or drainage ditch), and ensures that linear features and polygon edges are maintained in a triangulated irregular network (TIN) surface model, by enforcing the breaklines as TIN edges. They are generally synonymous with three-dimensional (3D) breaklines because they are depicted with series of x, y, z coordinates.

  • A hard (sharp) breakline defines interruptions in surface smoothness (for example, to define streams, rivers, shorelines, dams, ridges, building footprints, and other locations) with abrupt surface changes.

 

 

CANOPY HEIGHT MODEL

A digital representation showing the height of the vegetation above the ground surface.

 

CARTOGRAPHY

 (from Greek χάρτης khartÄ?s, "map"; and γράφειν graphein, "write") is the study and practice of making maps. Combining science, aesthetics, and technique, cartography builds on the premise that reality can be modeled in ways that communicate spatial information effectively.


https://en.wikipedia.org/wiki/Cartography


CLASSIFICATION (OF LIDAR)

The classification of lidar point cloud returns in accordance with a classification scheme to identify the type of target from which each lidar return is reflected. The process allows future differentiation between bare-earth terrain points, water, noise, vegetation, buildings, other man-made features and objects of interest.


CONTOUR MAP

A line map demarking lines of constant elevation across a terrain surface.  It is often included in a topographical map.

 


DEM (DIGITAL ELEVATION MODEL)

A collection of three dimensional points in a grid or random arrangement to represent or derive a Bare Earth surface.


DGPS (DIFFERENTIAL GLOBAL POSITIONING SYSTEM)

Is an enhancement to Global Positioning System that provides improved location accuracy, from the 15-meter nominal GPS accuracy to about 10 cm in case of the best implementations.
 DGPS uses a network of fixed, ground-based reference stations to broadcast the difference between the positions indicated by the GPS (satellite) systems and the known fixed positions. These stations broadcast the difference between the measured satellite pseudorangesand actual (internally computed) pseudoranges, and receiver stations may correct their pseudoranges by the same amount. The digital correction signal is typically broadcast locally over ground-based transmitters of shorter range.

https://en.wikipedia.org/wiki/Differential_GPS
 


DSM (DIGITAL SURFACE MODEL)

A collection of three dimensional points and/or linework depicting breaklines and/or features to represent or derive a surface of all applicable terrain and features including: buildings, bridges, roads, vegetation and hydrology.


DTM (DIGITAL TERRAIN MODEL)

A collection of three dimensional points and linework representing breaklines and/or features to represent or derive a Bare Earth surface.


FINAL RETURN

The Laser pulse echo that is associated with the lowest object In the path of the laser beam (often the ground)


GIS (GEOGRAPHIC INFORMATION SYSTEM)

A system designed to capture, store, manipulate, analyze, manage, and present all types of spatial or geographical data. The acronym GIS is sometimes used for geographical information science or geospatial information studies to refer to the academic discipline or career of working with geographic information systems and is a large domain within the broader academic discipline of Geoinformatics.[1] What goes beyond a GIS is a spatial data infrastructure, a concept that has no such restrictive boundaries.


https://en.wikipedia.org/wiki/Geographic_information_system
 


GPS (GLOBAL POSITIONING SYSTEM)

Is a space-based navigation system that provides location and time information in all weather conditions, anywhere on or near the earth where there is an unobstructed line of sight to four or more GPS satellites.[1] The system provides critical capabilities to military, civil, and commercial users around the world. The United States government created the system, maintains it, and makes it freely accessible to anyone with a GPS receiver.


https://en.wikipedia.org/wiki/Global_Positioning_System


HILLSHADE MAP

A georeferenced rendering of a Bare Earth model to give a digital raster image the impession of a 3D shape through the application of shadows derived as a function of terrain slope and artificial sun angle.


HYDROLOGICALLY FLATTENED (HYDRO-FLATTENED)

Processing of a LiDAR-derived surface (DEM or TIN) so that standing water bodies are flat and flowing water bodies are level from bank-to-bank. Additionally, surfaces of streams, rivers, and long reservoirs demonstrate a gradient change in elevation along their length. In traditional maps that are compiled photogrammetrically, this process is accomplished automatically through the inclusion of measured breaklines in the DTM. However, because LiDAR does not inherently include breaklines, a DEM or TIN derived solely from LiDAR points will depict water surfaces with unsightly and unnatural artifacts of triangulation. Hydro-flattening typically involves the addition of corrected breaklines along the banks of the specified water bodies. These breaklines establish elevations for the water surfaces that are consistent with the surrounding topography, and produce aesthetically acceptable water surfaces in the final DEM or TIN.


IMU (INERTIAL MEASUREMENT UNIT)

An electronic device designed to measure and record or report inertial/gravitational forces acting on it.  The types of forces are both angular (rotational) and linear, acceleration.  Highly accurate and precise three axis gyroscopes and accelerometers, respectively, are employed for these measurements.  Magnetometers are sometimes used to enhance or provide an initial reference for the inertial components of the device.  An IMU, in spite of its precision and accuracies is still a victim of physics.  Without supporting GPS style electronics, its data can only support absolute positioning necessary for mapping, from a few seconds to a few minutes before “drift” takes its toll on accuracy.  Its primary purpose for this application is to highly enhance extrapolation of coordinates between GPS readings.  Errors in GPS reading can also be flagged as excessive residuals from IMU derived coordinates to GPS coordinates over a short time frame.<


INITIAL RETURN

The Laser pulse echo that is associated with the first reflective object below the aircraft.


INTENSITY IMAGE

A georeferenced image constructed to show the echo strength of all valid returned infrared laser pulses.  This product appears as a grainy panchromatic image where shading is proportional to surface reflectance of infrared light at the angle of laser incidence.


LIDAR

(also written LIDAR, LiDAR or LADAR) is a remote sensing technology that measures distance by illuminating a target with a laser and analyzing the reflected light. Although thought by some to be an acronym of Light Detection And Ranging,[1] the term lidar was actually created as a portmanteau of "light" and "radar".[2][3] Lidar is popularly used as a technology to make high-resolution maps, with applications in geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, remote sensing, atmospheric physics,[4] airborne laser swath mapping (ALSM), laser altimetry, and contour mapping.


https://en.wikipedia.org/wiki/Lidar
 

LiDAR was first used in 1963


MULTIPLE RETURNS

Many modern LiDAR units are capable of detecting numerous echos from a single pulse of light.  Part of the laser beam may hit a tree branch (return 1 or initial return) another part my hit a leaf (return 2) another part may it a low shrub (return 3) another part may hit the ground (return 4 – final return)


ORTHOPHOTO

An orthophoto, orthophotograph or orthoimage is an aerial photograph geometrically corrected ("orthorectified") such that the scale is uniform: the photo has the same lack of distortion as a map. Unlike an uncorrected aerial photograph, an orthophotograph can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for topographic relief,[1]lens distortion, and camera tilt.
Orthophotographs are commonly used in the creation of a Geographic Information System (GIS). Software can display the orthophoto and allow an operator to digitize or place linework, text annotations or geographic symbols (such as hospitals, schools, and fire stations). Some software can process the orthophoto and produce the linework automatically.


https://en.wikipedia.org/wiki/Orthophoto


PHOTOGRAMMETRY

The discipline of making measurements from photographs, especially for recovering the exact positions of surface points. Moreover, it may be used to recover the motion pathways of designated reference points located on any moving object, on its components and in the immediately adjacent environment. Photogrammetry may employ high-speed imaging and remote sensing in order to detect, measure and record complex 2-D and 3-D motion fields (see also sonar, radar, lidar etc.). Photogrammetry feeds the measurements from remote sensing and the results of imagery analysis into computational models in an attempt to successively estimate, with increasing accuracy, the actual, 3-D relative motions within the researched field.


https://en.wikipedia.org/wiki/Photogrammetry

 


POINT CLOUD

A large collection of three dimensional points usually obtained by LiDAR.  Originally, point clouds contained only XYZ spatial information, however, this GIS datatype is evolving to include chromatic, reflectant intensity, feature classification and other information.  The positional interrelationship of the points with sufficient density resolves identifiable topographic features and structures.   The image brought to mind by the term "point cloud", accurately describes its appearance.


PULSE

A burst of laser light that is emitted from a LiDAR unit, usually toward the ground.


PULSES PER SQUARE METER

A measure of the density of LiDAR.  The number of pulses that hit each square meter of the surface of the earth.


RETURN

Laser light that is detected by a LiDAR unit after it reflects off of a target (ground).


SLOPE MAP

Shows the slope (steepness) of the terrain in a Bare Earth Model.  These maps can be represented in various forms to show magnitude, direction or regions of slope of a given range.  The latter to highlight areas of interest for development or study of various land uses.


TIN (TRIANGULATED IRREGULAR NETWORK)

A digital data structure used in a geographic information system (GIS) and other software applications for the representation of a surface. A TIN is a vector-based representation of a physical surface, made up of irregularly distributed three dimensional (3D) nodes with lines linking each node to it's neighbors, forming a 3D structure of non-overlapping triangles. Each triangle can be considered a face onto which digital imagery can be projected to provide an amazingly real 3D digital model.

TIN's are also the foundation from which terrain contours are generated, accurate slope and volume calculations are done.

 
VECTOR
A line depicted by two points (cartesian), a start point and an end point; or a start point and one or two relative angles (Polar) and a magnitude/length.