Differences

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--- terminology [2018/10/09 16:37] – allchin09
+++ terminology [2018/10/09 17:29] (current) – allchin09
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 |Coordinate transformation| Change of coordinates from one CRS to another, where the CRSs datums differ|
 |Datum| Defines the position of the origin, the scale and the orientation of the axis of a coordinate system with respect to an object|
+|Easting| Distance in a CRS eastwards from a north-south reference line, positive eastwards|
+|Ellipsoid| A closed surface formed by the rotation of an ellipse about a main axis. The figure of the Earth is usually modelled as an ellipsoid which is slightly squished from the shape of a sphere at the poles. Shape usually described by terms //a// and //b// (semi-major and semi-minor axis lengths) or //a// and //f-inverse// (inverse flattening)|
+|Ellipsoidal height (//h//)|Distance of a point from the ellipsoid, measured along the perpendicular from the ellipsoid to the point|
+|Geodetic CRS|A CRS where position is specified by geodetic latitude, geodetic longitude and (for 3d case) ellipsoidal height|
+|Geodetic latitude| Angle from the equatorial plane to the perpendicular to the ellipsoid through a given point, positive northwards|
+|Geodetic longitude| Angle from the prime meridian plane to the meridian plane of a given point, positive eastwards|
+|Geoid| Equipotential surface of the Earth's gravity field, which is everywhere perpendicular to the direction of gravity and which best fits mean sea level|
+|Geoid-ellipsoid separation (//N//)|Height of the geoid above the ellipsoid|
+|Gravity-related height (//H//)|Height dependent on the Earth's gravity field, such as orthometric or normal height, which both are approximations of the distance of a point above mean sea level. //H// = //h// + //N//|
+|Height| Either ellipsoidal or gravity-related height|
+|Map projection| Coordinate conversion from an ellipsoidal coordinate system to a plane|
+|Mean sea level (//MSL//)| Averal level of the surface of the sea over all stages of tide and seasonal variations. Usually defined for a local region from observations of one or more points over a period of time|
+|Meridian| Intersection of an ellipsoid by a plane containing the shortest axis of the ellipsoid|
+|Northing| Distance in a CRS from an east-west reference line, positive northwards|
+|Prime meridian| Meridian from which the longitudes of other meridians are quantified|
+|Projected CRS| A CRS derived from a 2D geodetic CRS by applying a map projection|
+|Vertical CRS| A 1D CRS based on a vertical datum|
+|Vertical datum| A datum describing the relation of gravity-related heights or depths to the Earth, usually related to //MSL//. Ellipsoidal heights are instead treated as being related to a 3D ellipsoidal CRS|