China
Africa
Explore chapters and articles related to this topic
*
Published in Giorgio Franceschetti, Riccardo Lanari, Synthetic Aperture Radar Processing, 2018
Giorgio Franceschetti, Riccardo Lanari
At this stage target heights do not explicitly appear. Usually heights are provided over the Earth ellipsoid (ellipsoidal height). A universal ellipsoid, which best approx-imates the whole surface of Earth, is the World Geodetic System (WGS84) ellipsoid. In the WGS84 reference system, each point is specified by the following coordinates (Figure 31): longitude (λ), latitude (ϕ), and height over the ellipsoid (z). To evaluate these new coordinates, we should transform the original (X, Y, Z) values onto the new ones (λ, ϕ, z). This is an easy coordinate transformation that is carried out via standard procedures (Schreirer, 1993). The new coordinates are referred to as geographic coordinates. Sometimes the heights are subsequently referred to Earth’s geoid (geoidal height).
Active Microwaves
Published in Iain H. Woodhouse, Introduction to Microwave Remote Sensing, 2006
The geoid is not always the best reference surface, however — what is “mean sea level” to someone living in Switzerland? The geoid is also difficult to use for mapping purposes since it is a real property that must be measured, rather than being a mathematically well-defined reference surface. The latter are referred to as ellipsoids, which are created to provide a common reference surface in order to define vertical location and to form the basis of map projections. In Chapter 10 we will discuss the need for some reference surface onto which we can project our radar image. WGS84 (the World Geodetic System defined in 1984) in one such global ellipsoid that is commonly used in planetary-scale studies and Earth observation. Ellipsoids
Co-ordinate reference systems
Published in Martin Vermeer, Antti Rasila, Map of the World, 2019
The reference ellipsoid used by the GPS is the ellipsoid of the WGS84 (World Geodetic System 1984). It is in principle the same as GRS80, but, due to reasons related to numerical computational imprecision (NIMA, 3 January 2000, § 3.2.2), it has a slightly different flattening, see Table 10.3. As a result, the semi-minor axis of WGS84, its polar radius, is 0.1 mm shorter than the one from GRS80.5
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.
Microstructural characterisation and analysis of coarse aggregates in asphalt drill cores
Published in Road Materials and Pavement Design, 2023
Tim Teutsch, Lukas Gönninger, Matthias Ruf, Holger Steeb, Wolfram Ressel
Therefore, a representative ellipsoid is fitted to the surface of each aggregate, as its mathematical form can be easily determined and reproduced. An ellipsoid represents the three-dimensional form of an ellipse and is defined by nine parameters. The position within a coordinate system is given by its centre (C), represented by three Cartesian coordinates (, , ). As shown in Figure 10(b), the dimensions are determined by three radii (, , ), which are orthogonal to each other and defined in the ellipsoids centre C. The longest dimension is defined by the radius , while the shortest is specified by , so represents the intermediate dimension. The indices indicate the local coordinate axis in which direction the expansion is defined. The orientation of the ellipsoid within a global Cartesian coordinate system is defined by three orientation angles, between the global and the local coordinate system axis. As also shown in Figure 10(b), the angle defining a rotation around the local x-axis is defined as . Meanwhile the rotation around the y-axis respectively, the z-axis the angles are defined as and . Due to the characteristic, that ellipsoids are symmetrical in their extension along their axes regarding the centre the orientation angles can be summarised in their magnitude. This leads to the following definition of the angles: , and . So if all angles (α, β, γ) equal to 0, the ellipsoid would be orientated alongside the global coordinate axis, with the longest radius along the x-axis, the intermediate radius along the y-axis and the shortest radius along the z-axis. These definitions will be used throughout the analysis in this contribution.