2. Seven-parameter method of bursa of fabricius:
The standard seven-parameter method uses X, Y, Z translation, X, Y, Z rotation and K scale, which is widely used and far away. It is usually used for the conversion from WGS84 in RTK mode or RTD mode to Beijing 54 and National 80. There are more than three known points and the requirements are higher.
3. Four parameters+elevation fitting: X, Y translation, A rotation, K scale and elevation fitting parameters are all used, which is also a common operation mode of RTK. Four parameters are used to complete the transformation from WGS84 plane to local plane, and elevation fitting is used to complete the fitting of WGS84 ellipsoid height to local plane.
Extended data:
1, four-parameter description: Four-parameter model (mathematical equation) is usually used when converting between two different two-dimensional plane rectangular coordinate systems. There are four unknown parameters in this model, namely:
(1) Two coordinate translation quantities (△X, △Y), that is, the coordinate difference between the coordinate origins of two plane coordinate systems.
(2) The rotation angle a of the plane coordinate axis. By rotating an angle, the X and Y axes of the two coordinate systems can overlap.
(3) The scale factor k, that is, the ratio of the length of the same straight line in two coordinate systems, realizes the scale conversion. Usually the value of k is almost equal to 1.
(4) Usually, at least two known points and four pairs of XY coordinate values in two different plane rectangular coordinate systems are needed to calculate these four unknown parameters. After calculating these four parameters, the XY coordinate value of a point in the plane rectangular coordinate system can be converted into the XY coordinate value in another plane rectangular coordinate system through the four-parameter equations.
Seven-parameter explanation: when converting between two different three-dimensional rectangular coordinate systems, a seven-parameter model (mathematical equation) is usually used, in which there are seven unknown parameters, namely:
(1) Three coordinate translations (△X, △Y, △Z), that is, the coordinate difference between the coordinate origins of two spatial coordinate systems.
(2) Rotation angles of three coordinate axes (△α, △β, △γ)). By rotating three coordinate axes to specify an angle, the XYZ axes of two spatial cartesian coordinate systems can overlap.
(3) Proportional factor k, that is, the ratio of the length of the same straight line in two spatial coordinate systems, realizes proportional conversion. Usually the value of k is almost equal to 1.
(4) Usually at least three common known points and six pairs of XYZ coordinate values in two different rectangular coordinate systems are needed to calculate these seven unknown parameters. After these seven parameters are calculated, the XYZ coordinate value of a point in a spatial rectangular coordinate system can be converted into the XYZ coordinate value in another spatial rectangular coordinate system through the seven-parameter equation.