Common coordinate systems, coordinate transformations and common problems in ArcGIS
1. Commonly used coordinate systems in ArcGIS
1. Geographic Coordinate System (Geographic Coordinate System)
Geographical coordinates are spherical coordinates, which are often displayed in decimal systems or units of degrees, minutes and seconds. The commonly used geographic coordinate systems are GCS_Xian_1980, GCS_WGS_1984, GCS_China_Geodetic_Coordinate_System_2000 The common parameters of the geographic coordinate system are as follows:
Angular Unit: Degree (0.0174532925199433)/Angular Unit
Prime Meridian: Greenwich (0.0)/Starting Longitude
Datum: D_China_2000/
Spheroid: CGCS2000/
Semimajor Axis: 6378137.0/Long Half Axis
Semiminor Axis: 6356752.314140356/
Inverse Flattening: 298.257222101/Inverse Flattening:
2, Projected Coordinate System (Projected Coordinate System) The
geographic coordinate system becomes a projected coordinate system after map projection. The map projection is based on certain mathematics The law converts the latitude and longitude coordinates of a point on the ellipsoid of the earth to rectangular coordinates on the plane. One point needs to be explained. The coordinate system is also called a spatial reference.
The main parameters of the projection coordinate system are:
CGCS2000_3_Degree_GK_CM_102E
WKID: 4543 Permission: EPSG
Projection: Gauss_Kruger/projection
False_Easting: 500000.0/Easting pseudo-offset
False_Northing: 0.0/Northing pseudo-offset
Central_Meridian: 102.0/Central Meridian
Scale_Factor: 1.0/
Latitude_Of_Origin: 0.0/Starting Origin
Linear Unit: Meter (1.0)/Linear Unit
Projection Coordinate System=Geography Coordinate system + projection
2. Coordinate conversion in
ArcGIS Common coordinate conversions in ArcGIS include geographic coordinate system to projected coordinate system, projected coordinate system to geographic coordinate system, the change of the projected coordinate system under the same reference datum, and the difference between the projected coordinate system. Conversion between belt modes, coordinate conversion between different reference datums, etc. The coordinate system conversion can theoretically be carried out between any two coordinate systems covering the data range.
For the three-dimensional coordinate conversion between different reference datums, the conversion process needs to provide seven parameters (3 translation parameters, 3 rotation parameters, 1 scaling parameter) before the conversion can be performed, because my country’s Beijing 54, Xi’an 80, and National 2000 reference The conversion parameters between datums are not disclosed, so the coordinate conversion between different reference datums generally involves the conversion of relevant departments.
The conversion between two-dimensional plane coordinates between different reference datums requires four parameters (2 translation parameters, 1 rotation parameter, and 1 scaling parameter) to be accurately converted.
3. Coordinate conversion method (same datum plane)
1. Vector data
ArcToolbox—data management tool—projection and transformation—element—projection
This conversion method is suitable for the following coordinate conversion of vector data:
3 degree belt to 6 degree belt, 6 degree Belt to 3 degree belt, geographic coordinate system to projected coordinate system, projected coordinate system to geographic coordinate system, central meridian to belt number, belt number to central meridian, conversion of different belt numbers.
2. Raster Data
ArcToolbox—Data Management Tool—Projection and Transformation—Raster—Projection Raster
This conversion method is suitable for the following coordinate conversion of raster data:
3 degree belt to 6 degree belt, 6 degree belt to 3 degree belt , Geographic coordinate system to projected coordinate system, projected coordinate system to geographic coordinate system, central meridian to belt number, belt number to central meridian, conversion of different belt numbers.
Note: When using the projection and projection grid tools, you must ensure that the original coordinates of the data must be correct, otherwise errors will occur when using them.
Fourth, several coordinate concepts that are easy to confuse in ArcGIS
1. The true coordinate of the data, referred to as "true coordinate system"
The true coordinate system of data refers to the coordinate system corresponding to the data record itself.
2. The nominal coordinate system of the data attribute, referred to as "attribute coordinate system" The
attribute coordinate system refers to the nominal coordinate system of the attribute of the data file. Right-click the data file in the data directory, you can directly modify the coordinate system in the file properties.
3. The data frame coordinate system in ArcMap, referred to as "map coordinate system"
, must be the projected coordinates of the data frame displayed in ArcGIS. Therefore, the coordinates displayed in the data frame are often inconsistent with the real coordinates of the data. For this kind of problem, it is necessary to ensure that the data is completely consistent with the coordinate system of the data frame.
5. How to get the correct coordinate system of the data (coordinate system guessing)
Coordinate system guessing refers to guessing the real coordinate system of the data, and setting the attribute coordinate system of the data to the real coordinate system. It may be due to confidentiality or wrong operation. Sometimes the coordinate system of the data we obtain is unknown or incorrect. At this time, we need to find a way to obtain the correct coordinate system.
In this case, there are generally the following processing methods:
1. Ask the data provider what the real coordinate system of the data is.
2. Check whether there is an .xml file in the given data list, this file is the data header file. If so, open it with Notepad, which records the creation time, storage location, coordinate system and other information of the file.
3. If you have to guess the true coordinate system of the data, the basic principle is to guess based on the characteristics of the coordinate value of the data. Experience will be important. If the coordinate values of the data look like latitude and longitude values, then it can be assumed that the data uses a geographic coordinate system. If the coordinate value of the data is the length of the ground (usually a large value), then the real coordinate system can be basically regarded as the projected coordinate system. If you know the approximate spatial range of the data, you can find out any "reference data" with the correct coordinate system in the spatial range, load it into the same map with the "target data" whose attribute coordinate system is unknown, and set the map coordinates The system is set to the projected coordinate system you suspect. When the target data matches the reference data range, it can be guessed that the suspected projected coordinate system is the true coordinate system of the target data, and other means can be used for verification. There can be many suspected projected coordinate systems. Which projected coordinate system to choose as the suspect object needs to be judged based on experience based on the coordinate value characteristics of the data. For example, the size of the X coordinate value of the data in the projection coordinate system with and without projection band number is obviously different in many cases.