In WebGIS development, common map reference systems include the following:
1. Geographic coordinate system: Also known as the geodetic coordinate system, a coordinate system based on longitude and latitude measurements on the Earth's ellipsoid.
2. Projected coordinate system: A coordinate system that maps points on the earth's surface to a flat map. Common projection methods include Mercator projection, Lambert projection, equiangular conic projection, etc.
3. CGCS2000 uses Gauss-Krüger projection
In WebGIS applications, to ensure data accuracy and consistency, the same map reference system as the geographic data source should be used. If you need to convert coordinates between different map reference systems, you can use a dedicated map projection tool to perform the conversion.
WGS84（World Geodetic System 1984）：
WGS84 is the currently widely used earth coordinate system. Its datum is defined by the semi-major axis and oblateness of the earth's shape.
Web Mercator Projection:
Web Mercator projection is a projection method designed for quickly displaying maps in WebGIS applications. It uses linear transformations in longitude and latitude so that the map can maintain a right-angled rectangular shape at any zoom level.
CGCS2000
CGCS2000 (China Geodetic Coordinate System 2000) is China's geodetic coordinate system, used to represent the geographical location within China. It is an earth coordinate system mainly used for surveying and geolocation. CGCS2000 defines the shape of the earth and the measurement reference system in China, including ellipsoid parameters and geodetic datum.
Although CGCS2000 is an earth coordinate system, it can be used for cartography and the representation of geospatial data. Commonly used projection methods for map drawing, such as Mercator projection, Lamberto projection, etc., can convert geographical data in the CGCS2000 coordinate system into a plane coordinate system to facilitate map display and visualization.
CGCS2000, as an earth coordinate system, can be used for the representation and conversion of map coordinate systems, but it is more used for measurement and geographical positioning, as well as for data processing and spatial analysis in geographic information systems (GIS).
The difference between CGCS2000 and WGS:84
CGCS2000 is China Geodetic Coordinate System 2000, a geodetic coordinate system released by China's National Geodetic Survey in 2000. It is based on the earth's center of mass, adopts the spatial coordinate system of the International Terrestrial Reference System (ITRS), and uses the International System of Units (SI) to define geodetic coordinates. CGCS2000 has been widely used in mainland China and its adjacent areas, such as map mapping, GPS navigation, earthquake monitoring, engineering surveying and other fields.
WGS 84 is the geodetic coordinate system used by the Global Positioning System (GPS). It is operated by the U.S. Department of Defense and the National Geospatial-Intelligence Agency.
(NGA) jointly released in 1984, it is based on the earth's center of mass, adopts the spatial coordinate system of the International Terrestrial Reference System (ITRS), and uses the International System of Units (SI) to define geodetic coordinates. WGS 84 is widely used in GPS positioning, map drawing, navigation, aviation, surveying and mapping and other fields.
The main difference between the two is the difference in their reference ellipsoids
The reference ellipsoid used by CGCS2000 is GRS80 (Geodetic Reference System 1980), while the reference ellipsoid used by WGS 84 is the WGS84 reference ellipsoid.
Although both reference ellipsoids are based on the same Earth model, their parameters are slightly different, so there may be slight differences in different applications.
In addition, the coordinate origins of the two geodetic coordinate systems are not exactly the same, so you need to pay attention to the difference when using them.
Tips: In the Openlayers code, there is basically no difference in performance between the two.
How to convert CGCS2000 to WGS:84 in Openlayers
// 定义CGCS2000和WGS84的投影信息
var cgcs2000Proj = new ol.proj.Projection({
code: 'EPSG:4490',
units: 'm'
});
var wgs84Proj = new ol.proj.Projection({
code: 'EPSG:4326',
units: 'degrees'
});
// 定义⼀个坐标点（以经纬度为例）
var point = ol.proj.fromLonLat([116.38, 39.9], cgcs2000Proj);
// 将坐标点从CGCS2000转换为WGS84
var wgs84Point = ol.proj.transform(point, cgcs2000Proj, wgs84Proj); // 打印转换后的坐标点
console.log(wgs84Point);