The datum transformation can be used between different datums of the same ellipsoid, or between different ellipsoids. The datum is generally defined by the transformation parameters from WGS1984 to the local datum. The datum is combined with the ellipsoid to approximate the Earth's surface. The relationship between the ellipsoid and the datum is one-to-many, that is, the datum is established on the basis of the ellipsoid, but the ellipsoid cannot represent the datum, and the same ellipsoid can define different datums. However, as the benefits of a global system outweigh the greater accuracy, the global WGS 84 datum has become widely adopted. OSGB36, for example, is a better approximation to the geoid covering the British Isles than the global WGS 84 ellipsoid. Because Earth is an imperfect ellipsoid, local datums can give a more accurate representation of some specific area of coverage than WGS 84 can. A horizontal datum is used to measure a location across the Earth's surface, in latitude and longitude or another coordinate system a vertical datum is used to measure the elevation or depth relative to a standard origin, such as Mean Sea Level (MSL). A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame) is a global datum reference or reference frame for precisely representing the position of locations on Earth or other planetary bodies by means of geodetic coordinates. Nuwa software supports some current mainstream reference ellipsoids, and it also support to add new one according to needs.ĭatum Transform -to define the datum Before understanding the datum transformation, it is necessary to understand the concept of geodetic datum and the relationship between datum and ellipsoid. The following table lists some of the most common reference ellipsoids: ![]() Because of their relative simplicity, reference ellipsoids are used as a preferred surface on which geodetic network computations are performed and point coordinates such as latitude, longitude, and elevation are defined. In geodesy, a Reference Ellipsoid is a mathematically defined surface that approximates the geoid, which is the truer, imperfect figure of the Earth, or other planetary body, as opposed to a perfect, smooth, and unaltered sphere, which factors in the undulations of the bodies' gravity due to variations in the composition and density of the interior, as well as the subsequent flattening caused by the centrifugal force from the rotation of these massive objects (for planetary bodies that do rotate). Ellipsoid -the reference ellipsoid As we all know, the surface of our earth is uneven, and for earth measurement, the surface cannot be expressed by mathematical formulas, and such a surface cannot be used as a datum for measurement and mapping. The coordinate system function in Nuwa includes five setting options: Ellipsoid, Projection, Datum Transformation, Plane Adjustment, and Height fitting. △ Projected Coordinate System : also known as a projected coordinate reference system, a planar coordinate system, or grid reference system, is a type of spatial reference system that represents locations on the Earth using Cartesian Coordinates (x,y) on a planar surface created by a particular map projection. Although latitude and longitude form a coordinate tuple like a Cartesian Coordinate System, the geographic coordinate system is not Cartesian because the measurements are angles and are not on a planar surface. △ Geographic Coordinate System(GCS) is a spherical or ellipsoidal coordinate system for measuring and communicating positions directly on the Earth as latitude and longitude. It is the simplest, oldest and most widely used of the various of spatial reference systems that are in use, and forms the basis for most others. Part 1 Coordinate System There are two coordinate systems to understand first. Next, the functions are explained one by one. ![]() ↑ CRS means Coordinate Reference System ↑ Let's take a picture to get a glimpse of their intricate relationship. Coordinate System? Parameters? Site Calibration?(I)Ĭoordinate System? Parameters? Site Calibration? Are you confused with these functions sometimes? First of all, their purposes are to obtain the final local coordinates, and some inconspicuous changes may affect the final result, caused coordinates error.
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