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The Earth and Its Coordinate System
Published in Terry A. Slocum, Robert B. McMaster, Fritz C. Kessler, Hugh H. Howard, Thematic Cartography and Geovisualization, 2022
Terry A. Slocum, Robert B. McMaster, Fritz C. Kessler, Hugh H. Howard
When creating a model of Earth, geodesists frequently utilize a reference ellipsoid, which is a smooth, mathematically definable figure that flattens at the poles and bulges at the Equator. Numerous reference ellipsoids have been developed, each defined by different parameters for the semimajor and semiminor axes, with the objective of trying to accurately map specific geographic extents (usually countries). In recent years, the reference ellipsoid concept has been updated to reflect accurate measurements of gravitational variation across Earth's surface. This variation has been modeled as a geoid, the two-dimensional curved surface Earth would take on if the oceans were allowed to flow freely over the continents. A datum combines the geoid and a specific reference ellipsoid to produce a reference for horizontal locations defined by latitude and longitude (established by the reference ellipsoid) and vertical elevations (defined by the geoid). The North American Datum of 1927 (NAD27) historically served as the basis on which the U.S. topographic mapping program was established but has been updated to the North American Datum of 1983 (NAD83). Ongoing satellite-based technologies (such as GNSS, GRACE-FO, and GRAV-D) have prompted new accurate modeling of Earth's horizontal and vertical datums, which will be updated to the National Spatial Reference System.
Sea Level Change and Its Potential Effects on Coastal Blue Carbon
Published in Lisamarie Windham-Myers, Stephen Crooks, Tiffany G. Troxler, A Blue Carbon Primer, 2018
Robert R. Christian, Eduardo Leorri, Linda K. Blum, Marcelo Ardón
We use the definitions from the Fifth Assessment Report by the Intergovernmental Panel on Climate Change (IPCC 2014). Specifically, we cite Chapter 13, “Sea Level Change,” by Church et al. (2013). First, RSL is “the height of the ocean surface at any given location, or sea level, is measured … with respect to the solid Earth” (pg. 1,142). Geocentric sea level relates to satellite altimetry and is measured relative to the reference ellipsoid. Sea level averaged over some time span to remove temporal variability is MSL. Generally, spatial averaging of MSL leads to global mean sea level (GMSL), although this might not be feasible for most of the geological record. For estimates in the geological record, far-field site or isostatic modeling are used (Dutton and Lambeck, 2012; Kopp et al. 2009, 2013), where models are typically tested against field data. This chapter focuses on the aspects of sea level most tied to the ability of coastal wetlands to sequester carbon. Therefore, emphasis is on RSL and its rate of rise. Other climate-related concerns are associated with the rates of SLR (e.g., hydrological cycle changes, intrusion of salt water). Further, while there is a tendency to focus on the rise in sea level, often records show a decrease under some circumstances. We use the word change when decreases in sea level may be an important component of the story.
Navigation
Published in Cary R. Spitzer, Uma Ferrell, Thomas Ferrell, Digital Avionics Handbook, 2017
Navigation is with respect to a coordinate frame of the designer’s choice. For navigation over hundreds of kilometers (e.g., helicopters), various map grids exist whose coordinates can be calculated from latitude and longitude. NATO helicopters and land vehicles use a Universal Transverse Mercator grid. Long-range aircraft navigate relative to an Earth-bound coordinate frame, the most common of which are (Figure 3.1) as follows: Latitude–longitude–altitude, measured with respect to a reference ellipsoid. The most useful reference ellipsoid is described in WGS-84 (1991). Longitude becomes indeterminate in polar regions, rendering these coordinates unsuitable there.Earth-centered rectangular (xyz). These coordinates are valid worldwide; hence, GPS calculates in them and often converts to latitude–longitude–altitude for readout.
Validation and application of model/reanalysis sea-level data to the establishment of the reference hydrographic surface in Spanish waters
Published in Journal of Operational Oceanography, 2023
Carlos J. González, J. Ramón Torres, Patricia Bernárdez, Rodolfo J. Ramos
The recent development of accurate geo-positioning by Global Navigation Satellite Systems (GNSS) has had direct application to modern Hydrography during the last two decades. The availability of precise measures of ellipsoidal and/or orthometric heights (i.e. vertical positions respect to reference ellipsoid and geoid, respectively) during hydrographic surveys has provided a new approach to the expression of sounding depths and the definition of the datum in nautical charts. In that respect, the International Federation of Surveyors (FIG) recommends the use of ellipsoidal heights for the establishment of vertical references (FIG 2006), such as the reference hydrographic surface (RHS), and the hydrographic services of different countries have been facing the problem during the last years (see, e.g. Dodd and Mills 2011; Turner et al. 2013; Yang et al. 2013; Slobbe et al. 2018). In waters of Spanish jurisdiction, this task is officially carried out by the Marine Hydrographic Institute of the Spanish Navy (IHM). The correct determination of ellipsoidally-referenced RHS allows for the production of seamless vertical data sets (IHO 2018) and an unambiguous transition between the official chart depths determined by IHM and the terrain altitudes established in Spain by the National Geographic Institute (IGN). In that respect, the International Hydrographic Organization (IHO) recommends the use of the lowest astronomical tide surface (LAT, which arises from the tidal harmonic prediction for a 19-year nodal period) as the basis of the RHS (IHO 2005).
A novel context-aware system to improve driver’s field of view in urban traffic networks
Published in Journal of Intelligent Transportation Systems, 2022
A. Nourbakhshrezaei, M. Jadidi, M. R. Delavar, B. Moshiri
where represents the vehicle movement. In order to prevent additional processing on the main server, the mentioned condition is checked on the client’s application. GPS positions are recorded as Latitude and Longitude with respect to the WGS84 reference ellipsoid. As the smartphone application is used to find the location of the vehicles, the accuracy of the positioning is related to the quality of the GPS antenna embedded in the smartphones. The mean accuracy in an urban environment is about 3 meters under good condition (Dabove & Di Pietra, 2019). However, there is a strong correlation between the accuracy and building’s height. The height of buildings can affect accuracy in two ways: a) Satellite signal blockage (Tirkas et al., 1998) and b) Signal reflection (multi-path) (Byun et al., 2002). These two errors decrease accuracy to up to 15 meters in some places. The accuracy is acceptable since the purpose of using GPS data in this research is to calculate the relative distance between camera’s location (east, west, north, south) and the vehicles near to RSU. To classify vehicles regarding their distances from the RSUs, ellipsoid curvilinear positions should be projected to the plane using UTM projection system.
A unified framework for passive–active fault-tolerant control systems considering actuator saturation and L∞ disturbances
Published in International Journal of Control, 2019
Mahmood Khatibi, Mohammad Haeri
There are generally two measures for describing the ‘largeness’ of an ellipsoid. One is its volume and the other is its shape. In this paper, the second measure is used. To be specific, the size of an ellipsoid is measured with respect to a reference ellipsoid.