The mutual conversion of several common coordinate systems
The conversion of the coordinate system is a problem we often encounter in the process of using geographic data, such as 54 to 80 to 80 to 2000, WGS84 to 2000, etc., and the geographic coordinate system to projected coordinates often mentioned in ArcGIS System, projected coordinate system to geographic coordinate system, 6° zone to 3° zone, cross-band conversion, etc. The conversion ideas are basically as follows:
1. Conversion between the geodetic coordinate system and the spatial rectangular coordinate
system Under the same coordinate reference system, the geodetic coordinate (B, L, H) and the inter-space coordinate system (X, Y, Z) can be directly converted by formula.
① Transformation from geodetic coordinate system (B, L, H) to spatial rectangular coordinate system (X, Y, Z)
②Conversion from space rectangular coordinate system (X, Y, Z) to geodetic coordinate system (B, L, H)
The conversion between the geodetic coordinates and spatial rectangular coordinates of the same reference datum needs to know the parameters of the ellipsoid.
2. Conversion between the geodetic coordinate system and the Gaussian rectangular coordinate
system Under the same coordinate reference system, the geodetic coordinate (B, L) and the Gaussian rectangular coordinate system (x, y) can be directly converted.
① Gaussian forward calculation: the conversion from geodetic coordinates (B, L) to Gaussian plane rectangular coordinates (x, y), the formula is omitted.
② Gaussian inverse calculation: the conversion from the Gaussian plane rectangular coordinate system (x, y) to the geodetic coordinate system (B, L), the formula is omitted.
3. Three-dimensional transformation of different geodetic coordinate systems (different reference datums)
The three-dimensional transformation of different reference datums generally calculates the conversion parameters through the relationship between the space rectangular coordinate systems, so it is necessary to convert the coordinate form to the space rectangular coordinate (X ,Y,Z), there are many conversion methods, the Bursa model is commonly used.
The conversion model requires seven parameters, namely: 3 translation parameters, 3 rotation parameters, and 1 scale change parameter. Therefore, the three-dimensional conversion of different geodetic coordinate systems requires seven parameters, which is also called 7-parameter conversion.
4. Conversion of two-dimensional plane coordinates. The plane coordinate transformation of a
small area can be two-dimensional coordinate transformation (also called four-parameter transformation). The two-dimensional transformation of different reference datums generally calculates the transformation parameters through the relationship between the plane rectangular coordinate system .
Four-parameter conversion requires four parameters: two translation parameters, one rotation parameter, and one scale change parameter.
**Extension:** When we use RTK to carry out surveying work, we often need to set four parameters. This is because the data collected by RTK defaults to the coordinates of WGS84, and the coordinate system frequently used in our country mainly includes: Beijing 54. Xi'an 80, National 2000, and the main purpose of setting the four parameters is to realize the conversion between the plane coordinates of WGS84 in a small area to other plane coordinates.