Coordinate System and Projection Transformation and Its Application in ArcGIS

Coordinate System and Projection Transformation and Its Application in ArcGIS

 

 

A batch of data needs to be processed recently, which involves the content of coordinate transformation. I will share my personal data collection and experience. please correct me if I have any shortcomings!

First, I would like to raise the following questions:
Is there a coordinate conversion problem? Is there a problem with projection conversion? What is the difference between coordinate conversion and projection conversion?

The following describes several concepts:
1. Earth elliptical body (Ellipsoid,Spheroid)
2. (Geodetic Datum)
3. GeographicCoordinate System)

4. Projection coordinate system (Projected Coordinate System)

The geographic coordinate system contains the Earth's elliptical body and the Earth's datum, that is, 3 contains 1 and 2;

The earth elliptical body contains the long half axis, short half axis, and flat rate of the selected elliptical body.
The projection coordinate system includes the required projection methods (Common projection methods include Gaussian-gram projection Gauss Kruger (Gk) and mocato projection mecator ), that is, the East pseudo offset, North pseudo offset, central meridian, scale, latitude origin, and meter unit.

The information mentioned above is known or contained in the file. The conversion parameter isThe is unknown.It contains the information of the conversion parameter. Only when the conversion parameter is available can the conversion between different coordinate systems be implemented.

Common coordinate transformations use the Bosa 7 parameter method:
1. DX--X axis offset
2. DY--Y axis offset
3. DZ--Z axis offset
4. WX--X axis rotation angle
5, WY--Y axis rotation angle
6. WZ--Z axis rotation angle
7. K-Scale

The other three parameters and four parameters can all be evolved from the seven parameters. Both the three parameters and the four parameters do not involve angle rotation.

Common coordinate systems:
1. The geocoordinate System (referred to as the geographical coordinate system in ArcGIS), also known as the longitude and latitude coordinate system, represents the method (B, l, h), B = longitude, L = latitude, H = altitude
2. Spatial Cartesian coordinate system (x, y, z), which is rarely represented by electronic maps.
3. Plane Cartesian coordinate system, Representation Method (X, Y, H)
Because 1 and 3 are mostly used for two-dimensional electronic maps, two digits are used to represent coordinates, that is, (B, L) and (x, y). h can be expressed as an attribute FIELD OF A element.

The following focuses on the earth coordinate system and the plane Cartesian coordinate system. What are the differences between the two coordinate systems? The earth coordinate system (I .e., the latitude and longitude Coordinate System) only contains the geographical coordinate system, while the plane Cartesian coordinate system includes both the geographical coordinate system and the projection coordinate system. Therefore, if only the Coordinate Systems of the earth are converted to each other, the projection transformation is not involved.

There are two Mutual Conversions between coordinate systems:

1. The reference elliptical body is the same, and the is different.
2. The earth datum is also different depending on the elliptical body.

In the first case, because the selected elliptical is the same, the center of the elliptical circle is consistent, but the size of the elliptical is different, that is, the scale is different. Theoretically, only one parameter (scale) is involved ), and because the starting point may be different, there will be an offset, the conversion requires four parameters (dx, Dy, DZ, K ).
In the second case, both the ball and the datum are different, and the 7-parameter method is required for conversion.
There is no conversion involved in projection transformation. arctool or other conversion tools can directly implement conversion without additional computing parameters.

There are three situations in which the Earth coordinate system is converted to the plane Cartesian coordinate system:

1. The reference elliptical body is the same, and the Earth datum is the same
2. The reference elliptical body is the same, and the is different.
3. The earth datum is different depending on the elliptical body.

Because the Cartesian coordinate system of a plane involves projection transformation, the projection parameters are required. The conversion between the coordinate system and the plane Cartesian coordinate system is to first convert the coordinate system to the space Cartesian coordinate, and then convert it to the plane Cartesian coordinate. For details, refer.

In the first case, only the projection parameters can be converted. For example, if the longitude and latitude of beijing 54 are converted to the Cartesian coordinate of beijing 54 plane, the conversion parameters are not required;
In the second case, four conversion parameters are required in addition to the projection parameters. Parameters must be provided or calculated based on two known points;
In the third case, the projection parameters and seven conversion parameters are required. Parameters must be provided or calculated based on three known points.

 

The following describes how to calculate parameters.

1. Three parameters -- 1 known point
2. Four Parameters -- two known points
3. 7 parameters -- three known points

You can use coord. EXE to calculate parameters. For more information, see tool help.

Summary: Before converting the data, you must first analyze the coordinate system information of the source data, and then determine whether the projection parameters and calculation conversion parameters are required (the projection parameters are generally included in the file), and finally implement the conversion.

Below are the gis27 brother of [Coordinate System and projection transformation and in the Desktop products of the application], address: http://bbs.esrichina-bj.cn/ESRI/viewthread.php? Tid = 20853 & extra = & page = 1

For personal documents, see the attachment.

Coordinate System and conversion documents: http://files.cnblogs.com/lauer0246/Coordinate_Convert1.rar

Coordinate Transformation and parameter calculation tool: http://files.cnblogs.com/lauer0246/Coordinate_Convert_Tool.rar