The coordinate system of data in SuperMap is divided into three categories: Planar Coordinate System, Geographic Coordinate System and Projected Coordinate System.
Planar Coordinate System
It is generally used as the coordinate reference of data unrelated to geographical location, and also the coordinate reference of new data by default, such as CAD design drawings, scanned pictures of paper maps, schematic diagrams unrelated to geographical location, etc. The Planar Coordinate System is a two-dimensional coordinate system with an origin at (0,0). The coordinates of each point in the data are determined by its distance from the horizontal and vertical X and Y axes.
Geographic Coordinate System
Use latitude and longitude coordinates to represent the coordinates of any point on the ellipsoid. The Geographic Coordinate System typically contains definitions for horizontal datum, Prime Meridian, and angular units. Commonly used Geographic Coordinate System include: WGS 1984, Beijing 1954, Clarke 1866, etc. For example, the KML data on Google Earth and the data collected by GPS are all based on WGS 1984. Xi'an 80 or Beijing 1954 is taken as the coordinate system for the coordinates of control points obtained by geodetic survey. The picture shows the World Map of WGS 1984 coordinate system.
Projected Coordinate System
Project any point on an ellipsoid onto a plane with a certain Projection Type and projection type. Use 2D plane coordinates (X, Y) to represent the position of a point-line-surface figure. The Projected Coordinate System usually contains the definitions of Geographic Coordinate System, map projection, Parameters, and Distance unit. Commonly used Projected Coordinate System include Gauss Kruger, Albers, Lambert, Robinson, etc. Generally, the projected geographic data can be used for Map Measurement, various Spatial Analysis, mapping expression, etc. For example, among the Basic Scale topographic maps in China, Lambert projection is used for 1:1 million topographic maps, and Gauss-Kruger 6 ° or 3 ° zone projection is used for most other topographic maps. The large-scale maps used in urban planning, such as 1:500, 1:1000 road construction drawings, architectural design drawings, etc., are mostly Planar Coordinate System. The figure shows the Robinson projection of the World Map in the original WGS 1984 coordinate system.
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Description of reference frame conversion method