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ITRF2020 (International Terrestrial Reference Frame 2020) is the latest earth reference frame officially released by the International Earth Rotation and Reference Systems Service (IERS) in 2022. The ITRF series is designed to define positions and motions on the earth with high precision. ITRF2020 is the successor to the traditional ITRF2014, and its updates are designed to improve the accuracy of observation techniques and respond to crustal movements. The reference frame is constructed from data from four observation techniques: VLBI (Very Long Baseline Interferometry), SLR (Satellite Laser Ranging), GNSS (Global Navigation Satellite System) and DORIS (Doppler Orbiting Integrated with Radio Positioning).

Baidu Coordinate System (BD09), also known as Baidu Coordinate System, is a coordinate system developed by Baidu to meet the special needs of geographic information systems in mainland China. It is encrypted based on the WGS84 coordinate system (World Geodetic System 1984) to ensure accurate geographic positioning services within mainland China.

GPS Coordinate System, that is, the coordinate system used by the Global Positioning System, is usually based on the geographic coordinate system (EPSG:4326) WGS84 (World Geodetic System 1984). This is a universal reference system used to determine the longitude and latitude of any point on the earth. WGS84 is a geocentric coordinate system with the center of mass of the earth as the origin. It is widely used in navigation, surveying, mapping and geographic information systems (GIS).

A projected coordinate system is a plane coordinate system whose map units are usually meters or kilometers. It is obtained from the projection of the earth’s approximate ellipsoid and corresponds to a geographic coordinate system. A projected coordinate system uses a coordinate system based on X and Y values to describe the location of a point on the earth.

Geographic Coordinate System (GCS) is a coordinate system based on a sphere or ellipsoid that is used to define locations on the surface of the Earth. It describes a location using two angular coordinates (usually latitude and longitude), and the third value can be an optional altitude value. GCS is widely used in fields such as geographic information systems (GIS), mapping, and navigation, and is the basis for expressing geographic data.

The 2000 coordinate system, namely the China Geodetic Coordinate System 2000 (CGCS2000 for short), is a new generation of geocentric coordinate system released by the National Administration of Surveying, Mapping and Geoinformation of China in 2008, replacing the Xi’an 1980 coordinate system. CGCS2000 adopts the standard of the International Terrestrial Reference Frame (ITRF) and is highly compatible with the WGS84 coordinate system (the earth coordinate reference system used worldwide). Its geodetic datum is based on the GRS80 ellipsoid (the 1980 International Reference Ellipsoid), with accurate geocentric positioning, and is suitable for various precise measurements and geographic information processing.

Goode Homolosine Projection is a map projection method proposed by John Paul Goode, an American geographer in the early 20th century. This projection combines the characteristics of the Mollweide Projection and the Sinusoidal Projection. It is an equal-area projection and can accurately represent the area of regions around the world.

Van der Grinten projection is a world map projection developed by American geographer Alphons J. van der Grinten in 1898. The notable features of this projection are that it can represent the entire earth in a circle and present a visually balanced and elegant world map by depicting the meridians and parallels as curves.

Stereographic projection is a method of projecting points on the surface of the earth or sphere from a certain point (usually a pole) of the sphere onto a plane. This projection method distributes points on the sphere and projects them from a certain point to the projection plane opposite it, and finally presents them in the form of a circular map. This method was invented by ancient Greek mathematicians and is widely used in many fields such as astronomy, crystallography and map making.

Mollweide Projection is an equal-area pseudocylindrical projection proposed by German mathematician Karl Brandan Mollweide in 1805. The projection maps the earth’s surface onto a flat surface through mathematical transformation, aiming to maintain the accuracy of area ratio while minimizing the distortion of shape and direction. The central meridian of the Mollweide projection is a straight line, the other meridians are symmetrical elliptical arcs, the parallels are parallel straight lines, and the length of the equator is twice the length of the central meridian.