Map projection
The purpose of choosing projections is to make the nature of the selected projection, and is suitable for the map of the map, while considering that the map is small in the layout range and is uniformly distributed. The map used in the sea is multi-use manifold, because it can maintain the correct position of the azimuth.
China's basic scale topographic map (1: 5,000, 1: 10,000, 1: 25,000, 1: 50,000, 1: 10,000, 1: 250,000, 1: 500,000, 1: 1 million), greater than Equal to 500,000, Gauss-Kruger, is a striped cross-cut elliptical projection, also called transverse mercator; less than 500,000 topographic maps are used, etc. The angle positive axial macating garden cone projection, is a lambert conformal conic; a topographic map of less than 500,000 is multi-use and other angular positive axis cylindrical projection, and the Mercator is called. A map projection system consistent with my country's basic proportional topographic map series should generally be used. The choice of the geodetic side of the earth is determined by the geodetic side and map projection, and the geodetic side is approximation using a particular ellipsoid on the specific region's Earth surface, so each country or region has its own geodetic side, we usually call Beijing 54 coordinate system, Xi'an 80 coordinate system actually refers to my country's two geodes of land. In the first Soviet Union, my country has established my country's Beijing 54 coordinate system from 1953. In 1978, I use the IAG 75 Ellipsoid recommended by the International Earth Measurement Association. - Xi'an 80 coordinate system, the result of the current GPS positioning belongs to the WGS84 coordinate system, the WGS84 reference surface adopts WGS84 ellipsoid, which is a coordinate system in the center of the ellipsoid. Therefore, there is a difference in the coordinates of their latitude and longitude relative to the same geographic location.
The three ellipsoid parameters used in this program are as follows (derived from "Global Positioning System Measurement Specification GB / T 18314-2001"):
Ellipsoid
Half-axis
Short half shaft
Krassovsky
6378245
6356863.0188
IAG 75
6378140
6356755.2882
WGS 84
6378137
6356752.3142
The relationship between the ellipsoid and the geodetic side is a pair of relationships, that is, the reference surface is based on the ellipsoid, but the ellipsoid cannot represent the reference surface, the same ellipsoid can define different reference faces, such as Former Pulkovo 1942 of the Soviet Union, the Afgoye reference papers in Africa Somalia have adopted Krassovsky ellipsoid, but their land reference faces are obviously different. In the current GIS commercial software, the geodial reference faces are defined by the conversion of the local reference face to the WGS84, that is, three translation parameters Δx, ΔY, Δz represent the translation value of the two situats; three rotation parameters εx, εy, εz indicates that the local coordinate system is rotated in parallel to the central coordinate system, respectively, respectively, respectively, respectively, respectively, respectively, respectively, the proportional correction factor, for adjusting the ellipsoid size. Beijing 54, Xi'an 80 relative to the conversion parameters of WGS84 have not been open, and the actual work can be used in Beijing 54 or Xi'an 80 coordinate control points to carry out the conversion of WGS84 coordinate values in the work area. Only one known control point is Under (ever), the difference between Beijing 54 and WGS84 coordinates is used as a translation parameter, when the work area is not large, such as Qingdao, the accuracy is also enough. Take (32 °, 121 °) 30 ° standard latitude latitude and ink trail projection results, Beijing 54 and WGS84 reference face, the projection results of the two are about 196 meters in the direction of the things, the north-south direction is about 57 meters (see table below ) For dozens or millions of maps, this error is not enough, but it should be considered in the engineering map. Enter coordinate (degree)
Beijing 54 Mo Carto projection (rice)
WGS84 Mo Carto projection (rice)
Latitude value (x)
32
3242287
3242230
Sleek value (Y)
121
11675036
11674840
Mercato projection (1) Mercator projection nature Mercator projected, also known as "Israel Positive Axis Cylinder Projection", Dutch Mercator 1512-1594) Demoned in 1569, It is assumed that the earth is surrounded by a hollow cylinder, and its equator is in contact with the cylinder, and then imagine that the center of the earth has a lamp, proceeds to the pattern on the spherical body, and then the cylinder is unfolded. This is a standard weft. The world map drawn for zero "Mo Catto). The ink Catto projected no angle deformation, and the length of each point is equal to each other. Its latitude and longline are straight lines, and the intersecting linear intervals, etc., the weft interval is gradually increased from the standard weft. The length and area deformation of the map projection of the ink trails is significantly, and the standard weft is not deformable, and the deformed line from the standard weft is increased, but because it has a variable-like expanded characteristic, the direction of the direction and the mutual positional relationship is maintained. The correctness of the direction and angle on the map is the advantage of the Mo Carto projection, and the Mo Carto projection map is often used as a navigation chart and aerospace map. If the straight line navigation between the two points on the Mo Carto projection, the direction can always be To reach the destination, it is positioned to the ship ship in the navigation, and it has a favorable condition to make a navigator. (2) Mo Carto projection coordinates to take zero mid-to-railing or custom origin, projection of the equator intersection, zero lunch or custom origin line projection is the longitudinal coordinate X axis, the equatorial projection is a horizontal coordinate Y-axis, constitutes ink Carto plane right angle coordinate system, this projection standard latitude has no deformation. Single point conversion single point conversion steps are as follows: (1) Select whether ink Carto positive conversion or reverse transformation, default is a latitude and longitude to the Mo Carto projection coordinates, the projection coordinate unit is rice. (2) Select the geodetic side, default Beijing 54, if it is GPS positioning data, don't forget to switch to WGS84. (3) Enter the standard latitude and unit degree. (4) Enter the origin of the origin, the unit degree, and default is zero. (5) If a forward projection, select the latitude and longitude input data format, there are three options, default to decurity format. The specific input method is as follows: format
Original latitude value
Original longitude value
Input latitude value
Enter longitude value
Decimal system
35.445901 °
122.997344 °
35.445901
122.997344
Degree
35 ° 26.7541 '
122 ° 59.8406 '
3526.7541
12259.8406
Degree
35 ° 26'45.245 "
122 ° 59'50.438 "
352645.245
1225950.438
(6) Positive projection According to the selected format, enter the latitude and longitude value in the "input" field, and the anti-projection input is based on the x, y coordinate value of the meter unit. (7) Click the Single Conversion button. (8) View the calculation result in the "Output" column. The batch conversion batch conversion steps are as follows: (1) Prepare the input data files that need to be converted, require the text file, divided into two columns, the first column latitude value or longitudinal coordinate value, the second column metric value or the lateral coordinate value, two columns Between separation between spaces. When projected, the latitude value and the longitude value format may have three options (see table), the default is treated as a decimal system; when reverse projection, the longitudinal and lateral coordinate values must be in meters. Below is an example of, hour (the WGS84) Mercator orthographic input data file testdata.txt 350000.000 1220000.000 351600.519 1225959.506 345800.101 1225959.8 343600.336 1230000.26 341400.018 1225959.897 335159.17 1225959.46 333000.08 1230000.28 332300.674 1232000.103 (2) selecting a conversion or positive anti Mercator Conversion, the default is the latitude and longitude to the Mo Carto projection coordinates, the projection coordinate unit is rice. (3) Select the geodetic side, default Beijing 54, if it is GPS positioning data, don't forget to switch to WGS84. (4) Enter the standard latitude, unit degree, such as "30", indicating the standard latitude 30 °. (5) Enter the origin of the origin, unit degree, default is zero. (6) If positive projection, select the latitude and longitude input data format in the input data file, there are three options to default to the decimal format. (7) Click the "Batch Conversion" button. The Open File dialog box will enter your data file name. (8) Enter the conversion result file name, click "Save", the program starts to calculate. (9) Open the output file to view the calculation result, the result is divided into five columns, the first sequence number, the second column input latitude value or the longitudinal coordinate value, the third column input longitude value or the lateral coordinate value, the fourth column conversion latitude value or portrait Coordinate values, fifth columns are converted to the manid value or the lateral coordinate value.
