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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
The relationship between the geoid and a chosen reference ellipsoid is important for a variety of mapping applications, especially large-scale mapping projects such as aeronautical charting, where coordinate or elevation accuracy is important. A geodetic datum10 is a model that describes the location, elevation, and scale relationships with respect to an origin on Earth's surface. There are two components to a geodetic datum: horizontal and vertical. A horizontal datum specifies locations in terms of geodetic latitude and longitude based on a chosen reference ellipsoid relative to an origin, which coincides with the Equator for latitude values and the Prime Meridian for longitude values. The horizontal datum specifies a precise description of the parameters for the reference ellipsoid so that the semimajor axis (equatorial radius) and flattening constant for Earth are known, thus providing an accurate means to establish latitude and longitude. A vertical datum provides a zero surface that enables elevations to be determined and, as mentioned earlier, is tied to the concept of mean sea level, which relates to the geoid. Although these two datum concepts have been historically separate entities because the surfaces to which they refer are different, they are commonly tied together today because they are conceptually and operationally related. For example, when surveying a new highway, surveyors need to accurately provide latitude and longitude based on a specific horizontal datum and a derived elevation value determined through the geoid.
Melting ice and rising seas – connecting projected change in Antarctica’s ice sheets to communities in Aotearoa New Zealand
Published in Journal of the Royal Society of New Zealand, 2023
Richard Levy, Timothy Naish, Daniel Lowry, Rebecca Priestley, Rachelle Winefield, Alanna Alevropolous-Borrill, Emory Beck, Rob Bell, Graeme Blick, Ruzica Dadic, Tasman Gillies, Nicholas Golledge, Zoe Heine, Stefan Jendersie, Judy Lawrence, Katherine O’Leary, Ryan Paulik, Ceridwyn Roberts, Mike Taitoko, Natalie Trayling
NZ SeaRise provided local sea level projections every ∼2 km along the coast of Aotearoa, but the projections were not connected to any specific elevation datum. Elevation data that seamlessly connect our land and sea are needed to improve estimates of the future position of key sea level datums (e.g. mean sea level, highest astronomical tide, total water level). These accurate projections of relative sea level are required to evaluate future coastline location and coastal flooding hazards. In this study we provided an example from Wellington Harbour where we connected local sea level elevation datums to the New Zealand Vertical Datum 2016. NZ SeaRise projections data were then used to project changes in the elevation of these key datums out to 2100 under SSP-2 4.5. Results suggest that plans to adapt to rising sea level will need to be developed and implemented well before the end of this century.
Development of Saudi continuous chart datum: Arabian Gulf case study
Published in Geomatics, Natural Hazards and Risk, 2019
Mohammed El-Diasty, Salim Al-Harbi, Spiros Pagiatakis
A continuous chart datum is a two-dimensional reference surface relative to a continuous vertical reference datum such as the Lowest Astronomical Tide (LAT) in Saudi Arabia or the reference ellipsoid (WGS84). It is realized by numerous hydrographic organizations around the world that the hydrographic vertical datum, such as a chart datum, now requires a continuous treatment. These continuous chart datums exist, most notably at the National Oceanic and Atmospheric Administration (NOAA’s VDatum datum, Gesch and Wilson 2001), the United Kingdom Hydrographic Office (UKHO’s VORF datum, Adams 2006; Iliffe et al. 2013), the Service Hydrographique et Oceanographique de la Marine (SHOM’s BATHYELLI datum, Pineau-Guillou and Dorst 2011), the Australian Hydrographic Service (AHS’s AusCoastVDT, Keysers, et al. 2013), Canadian Hydrographic Service (CHS’s CCVD datum, (Lefaivre, et al. 2010; De Lange 2012; Robin et al. 2012, 2016; ) and Dutch and Belgium vertical reference datum (NEVREF, Slobbe, et al. 2018). In this paper, the Saudi coastal mapping and monitoring (SCM2RS) group takes a lead in developing a Saudi continuous chart datum (SCCD) using the data collected from Saudi coastal areas along with the hydrodynamic ocean model.
A causative analysis on ECDIS-related grounding accidents
Published in Ships and Offshore Structures, 2020
İdris Turna, Orkun Burak Öztürk
According to Table 2, it is indicated that only 0.7% of the ENC charts that belong to coastal areas, in which running-aground accidents frequently occur, are described as an A1 region which is the most trusted category. It is known that the water surface levels also known as chart datum that is accepted as references for the soundings and vertical datum varies in the INT-type charts that are produced by the national hydrographic offices. It is notable that while some hydrographic offices prefer Lowest Astronomical Tide or Mean Low Water Spring (MLWS) for soundings, Mean Sea Level is preferred as a chart datum in others. Figure 3 shows the information of an ENC chart in which the MSL water level is preferred for soundings and vertical datum.