Conversion relationship calculation

Function Description

This function calculates the required conversion relationship based on the control point pair, and can save the calculated conversion relationship to the history file for reuse. Currently supports four-parameter and seven-parameter solutions.

Usage

Click Data Management> Projection and Coordinate Conversion> Conversion Relationship Calculation

Parameter Settings

• Parameter Solution：The method of parameter calculation supports four parameters and seven parameters.
• Source/target coordinate file：Input the control point source coordinate file, the format can be referred to Seven Parameter format.
• Source/target coordinate system：When the coordinate form is x y h / BLH, the coordinate system can be selected, please refer to Define Projection.
• Source/target coordinate form：
  • X Y Z (Earth-centered coordinate system): Select this item when the input data is in the projected coordinate system. At this time, the "source/target coordinate system" cannot be selected. Directly calculate the seven-parameter transformation between the source coordinate and the target coordinate. If the user selects four parameters, it will be forced to switch to X Y Z
  • X Y H / BLH: Select this item when the input data is in the projection/geographical coordinate system. At this time, you need to select the "source/target coordinate system". After the selection is completed, it will automatically switch once according to the selected coordinate system. When selecting BLH, you can select degrees or degrees: minutes: seconds.
    • x y h: The "source/target coordinates" will be projected to geographic coordinates according to the projected coordinate system selected by the user, and then the geographic coordinates will be transferred to the geocentric coordinate system according to the ellipsoid information in the projected coordinate system, and finally the seven parameters between the two geocentric coordinate systems will be solved.
    • BLH: The user needs to select "Geographic Coordinate System", the program transfers the coordinates to the geocentric coordinate system according to the ellipsoid information in the geographic coordinate system, and finally solves the seven parameters between the two geocentric coordinate systems.
  • Report：Calculate the conversion relationship and generate a report, which contains the calculated conversion relationship parameters and the back-projection report of various control points. The report can be saved as HTML and ASCII format.
  • Define conversion relationship：Please refer to Create Transformation.

Seven-Parameter Solution

Using Bursa model to calculate the seven parameters for the transformation among different coordinate systems according to three or more pairs of tie-points. The parameters include three translation parameters, dx, dy, dz, three rotation parameters, rx, ry, rz, and a scaling factor, m. The calculation formula is shown below. Bursa seven parameters formula can be written as follow:

Convert the above formula to a equation set, which is：

In the equation set, there are seven unknown parameters. If there are three or more than pairs of tie-points, these seven parameters can be solved through the above equation set using the least square method.

Four-Parameter Solution

According to two or more control points, users can calculate the four parameters that used to perform coordinate system transformation. The four parameters include two translation parameters, dx and dy, a rotation parameter, T, and a scaling factor, K.