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1、Walk地图投影使用说明（Walk map projection instructions）Walk map projection instructions1 the basic principle of geographical projectionThere are 2 commonly used map coordinate systems, the geographical coordinate system and the projection coordinate system (in fact, there is also a geocentric coordinate syst
2、em). The geographic coordinate system is the coordinate system based on latitude and longitude, and there are 2 important parts in the geographical coordinate system, namely, the earth ellipsoid (spheroid) and the earth datum (datum). Due to the irregular surface of the earth, it can not be used to
3、express the mathematical formula, it cannot implement operation, so must find an ellipsoid shape and size are very close to the earth instead of the earth, the ellipsoid is called earth ellipsoid, our common ellipsoid are as follows:Ellipsoid NameyearsLong axle (meter)Short half shaft (meter)Oblaten
4、essWGS84 19846378137, 6356752.3, 1:298.257J Lasovski (Krasovsky) 19406378245, 6356863, 1:298.3IAG-75 19756378140, 6356755.3, 1:298.257Table 1 commonly used ellipsoid in ChinaGeodetic datum refers to the current reference ellipsoid and WGS84 reference ellipsoid between relative position (3 translatio
5、nal, 3 rotational and 1 zoom), which can be used in 3, 4 or 7 parameters to describe the relationship between them, each ellipsoid corresponds to one or more datum.The projection coordinate system uses some mathematical rules to represent the longitude and latitude network on the surface of the eart
6、h to the plane, and belongs to the plane coordinate system. Mathematical law refers to the type of projection, widely used in China at present is Gauss, Krueger projection, in Europe and the United States called transverse Mercator projection (Transverse Mercator). The central longitude and equator
7、of the Gauss projection are perpendicular to each other, and the zonation is divided into 3 degrees and 6 degrees. The preparation of global transverse Mercator projection world military maps and earth resources satellite photograph used (UTM) is a variant of the transverse Mercator projection. The
8、central warp length ratio of the Gauss projection is equal to 1, and the UTM projection specifies the ratio of the central meridian length to 0.9996.Our country provides 1:1 million, 1:2.5 million, 1:5 million, 1:10, 10000, 1:25, 10000, 1:50, 000 scale topographic maps, all use Gauss gram grid proje
9、ction. From 1:2.5 to 1:50, the topographic map of 10 000 meters is divided by 6 degrees of longitude, and the topographic maps of 1:1 and 1:2.5 are adopted with 3 degrees of difference.2 Beijing 54 and Xian 80 coordinate systemFirst understand the concept of geodetic coordinates.Geodetic coordinate,
10、 the establishment of a series of connected triangles on the ground, take a precise distance as the starting point in this side, two side, using the method of astronomical observations to determine its position (longitude, latitude and azimuth), to determine the value of the angle of the triangle wi
11、th a precise angle measuring instrument, according to the initial boundary the length and position, you can calculate the coordinates of the other points. The coordinates thus calculated are called geodetic coordinates.The geodetic coordinate origin was set up in Beijing in 1954, and the coordinates
12、 of the geodetic control points were calculated as the 1954 Beijing coordinate system. In order to adapt to the development of geodesy, China adopted the IAG-75 geodetic ellipsoid recommended by the international geodetic Association in 1978 (named IAU76 in Proj4), and established a new geodetic coo
13、rdinate system in china,And in 1986 announced the establishment of the new geodetic coordinate origin in Jingyang County in Shaanxi Province, the geodetic coordinates of the control points are calculated out, known as the geodetic coordinate system 1980.The Beijing 54 or Xian 80 coordinate system, w
14、hich we often use for projection of images, is a projection Cartesian coordinate system. The following table shows the main parameters used in the 80 coordinate system of Beijing 54 and Xian,Coordinate nameProjection typeEllipsoidDatum planeBeijing 54 Gauss Kruger (Transverse Mercator) Krasovsky Bei
15、jing 54Xian 80 Gauss Kruger (Transverse Mercator) IAG75 Xian 80Table 2 list of commonly used coordinate system parameters in ChinaWe can see that the 54 Coordinate System and the Xian two coordinate system, which we usually call Beijing 80 coordinate system, are actually the three geodetic datum of
16、our country.3 parameter acquisitionFor geographical coordinates, only two parameters, namely ellipsoid and geodetic datum, need to be determined. For projective coordinates, the projection type is Gauss Kruger (Transverse Mercator - named tmerc in Proj4). In addition to determining the ellipsoid and
17、 geodetic datum, the central meridian is also determined.Determination of the geoid is the key to determine the 7 parameters (or several parameters), Beijing 54 datum can use three translation parameters, namely -12, -113, -41,0,0,0,0 , a lot of software is approximately Krasovsky (0,0,0,0,0,0,0) da
18、tum; Xian 80 of the 7 parameters is special, each region is not the same. There are two ways: one is directly obtained from surveying and mapping departments; two is the same point with coordinates to Xian 80 coordinate system and other coordinate system according to the value of more than three, ca
19、lculated using the software, this software has some green functions, such as Coord MG.There are two ways to obtain the central meridian. The first method is based on the known number of bands, 6 degrees with 6*N-3, and 3 degrees with 3*N; the second method is based on longitude, as shown in figure 1
20、.Fig. 1 the zoning of Gauss Krueger projectionDefining coordinates in 4 WalkIn the new layer of Walk, modify layer structure, workspace settings and other dialog boxes, projection. the button opens the map projection settings dialog box. After the projection is set or changed, the opened layer and d
21、ata loading / storage, and the Walk map roaming are automatically adapted to the new map projection.SampleThe following is a map of Chinas 400 and 1/10000.The layer coordinate system of Res1_4m layer is WGS84 coordinate system (Lat/Long).The workspace map projection is set to the Beijing 54 ellipsoi
22、d Lambert conical projection, as shown above.The map projection settings of the workspace are recorded in the wks file, and the layer coordinate settings are recorded in the Memo field of the walklayers table.Map projection settingsThe projection in the new layer, the modified layer structure, and t
23、he workspace, coordinate and measurement settings. the button opens the map projection settings dialog box.I. independent plane right angle coordinate systemAn independent plane Cartesian coordinate system without projection is used for spatial data in unknown or small space coordinate systems. The
24、original walk layer data is not projected, so it can be considered that the independent plane Cartesian coordinate system is adopted. For independent plane Cartesian coordinate systems,Walk system does not map projection transformation when data is read / saved.Two projectionWalk supports all 125 ba
25、sic projection types of Proj4, which are selected from the drop-down list box.When the projection type is selected, its full name and type are displayed. If the projection type is LCC, the full name is Lambert Comformal Conic, the type is Conic (conic projection), and the parameters listed in the pa
26、rameter list can be set by the projection.Three ellipsoidAny projection is applied to the ellipsoid, and Walk supports all 45 ellipsoids of Proj4. WGS84, karss and IAU76 are the three ellipsoid commonly used in our country. Including ID, long ellipsoid ellipsoid semi axis, and the flattening.Geodeti
27、c datum refers to the current reference ellipsoid and WGS84 reference ellipsoid between relative position (3 translational, 3 rotational and 1 zoom), which can be used in 3, 4 or 7 parameters to describe the relationship between them, each ellipsoid corresponds to one or more datum. Set the towgs84
28、item in the parameter list in Walk.Four, parametersThe parameters include two parts: geodetic datum and projection parameter. The geodetic reference parameter towgs84 can be either a three parameter or a seven parameter.As shown in the example above, towgs84=-12, -113, and -41 are the central transl
29、ations of the Beijing 54 ellipsoid and WGS84 on the web.Different projection types have different projection parameters, such as the LCC projection, the first standard parallel ring lat_1 and the second standard parallel circle lat_2. In the parameter list, any attribute (parameter) name prefix * en
30、try must be entered.Some parameters apply to any projection type, such as lon_0, x_0, and so on. Select a parameter in the parameter list, then edit the box under the parameter list box, enter the parameter value, and use the Modify button to enter the parameter value. For example, in the LCC projec
31、tion, in order to make our country in the center of the projection, set lon_0=108 (central longitude of our country).Five, projection commandEdit the projection command editor window to edit, and set the projection command directly as specified by proj4. The meanings of the common parameters are as
32、follows. For more parameter meanings, refer to the proj4 manual. You can add useful parameters yourself in the edit projection command.+a, Semimajor, radius, of, the, ellipsoid, axis+alpha, Used, with, Oblique, Mercator, and, possibly, a, few, others+axis, Axis, orientation (new, in, 4.8.0)+b, Semim
33、inor, radius, of, the, ellipsoid, axis+datum, Datum, name (see, proj, -ld)+ellps, Ellipsoid, name (see, proj, -le)+k_0 Scaling factor (new name)+lat_0 Latitude of origin+lat_1, Latitude, of, first, standard, parallel+lat_2, Latitude, of, second, standard, parallel+lat_ts, Latitude, of, true, scale+l
34、on_0 Central meridian+lonc, Longitude, used, with, Oblique, Mercator, and, possibly, a, few, others+ lon_wrap中心经度使用的包装（见下图）默认的项目。4套输出经度范围在180到180。+开关可用于禁用默认的包装是在pj_inv()低水平了。这是特别有用的预测一样，将理想的EQC的x值过去20000000（大约）继续过去而不是180包+ 180。+ lon_wrap选项可以用来提供做内包装的另一种手段pj_transform()经度。这个选项的参数是一个中心经度。所以lon_wrap =
35、180 +包经度范围在0到360。注意，+不+ lon_wrap禁用。+ nadgrids filename NTv2网格文件使用的数据转换（见下文）+ no_defs不使用/ usr /分享/项目/ proj_def.dat缺省文件+超过允许经度输出- 180到180范围，禁用包装（见下文）下午交替本初子午线（通常是城市名称，见下文）+项目名称（见投影项目-我）+南表示南半球UTM区+ to_meter乘法器转换映射单元到1.0M+ towgs84 3或7项基准转换参数（见下文）+单位米、美国测量尺等。+ x_0假东+ y_0北移+坐标区六、预览【预览】按钮按当前地图投影将世界经纬图绘制于右
36、侧的预览框中若当前的投影命令非法，将给出提示。walklayers表中投影定义图层中所有要素（地物、文字等）具有相同的坐标系，可以与他层和与工作空间的地图投影坐标系不同，要素加载到工作空间时系统自动将要素从所在图层坐标系变换为工作空间坐标系上，也就是说加载到内存的要素其坐标系已变换，因此不同坐标系的图层通过投影变换叠加在空间空间对工作空间中的要素编辑和修改后，保存时系统将要素变换回其层坐标系。图层地图投影坐标系设置后将保存在图层所在库的walklayers表的备忘录字段中，格式为：proj4 = ；（关于投影命令请参见上节）走系统会根据投影命令自动设置坐标单位coordunit为经纬度度单位，
37、13，7为投影坐标系米单位。The data ranges of the layers in the WalkLayers table, minE, minN, maxE, maxN, and so on belong to the layer coordinate system. In Walk roaming, the system will first reverse the projection layer correlation index lattice, and then load the data projection transformation.The SRS in the
38、 WalkLayers table is currently used only in the Geography of SQL Server 2008, SRID.Use the script to set the projection flexiblyUse the map projection settings dialog box can be set by layer, some cool projection can be realized by projection editing command. But if the use of the dialog box batch s
39、et is very tedious and error prone, so Walk provides a batch script can be set and dynamic settings. If two examples are attached to the system, the WalkLayers - layer coordinate system.Cpp is generated and the warp and weft network.Cpp is generated.The map projection function in the script is in th
40、e wkTrans class, projectCreate, projectFree, project, projectGet, and projectSet. In wkTrans, a map projection container is first created for projection, fetching, setting, and setting, and finally releasing the container.5 use map projectionCommon projections and geodetic datumCommonly used map pro
41、jection, Beijing 54, Xian 80, UTM, and local urban coordinate system.The main coordinate system adopted in our country1954 Beijing coordinate system (Beijing, Geodetic, Coordinate, System, l954)The coordinate system with the former Soviet Union in 1942 and the establishment of the coordinate measure
42、ment, its origin is not in Beijing, but in the Soviet Union pulkovo. The coordinate system adopts the J Lasovski ellipsoid (Krasovsky-1940) as the reference ellipsoid, and the elevation system adopts normal height, which is based on the mean sea surface of the Yellow Sea in 1956.1980 Xian coordinate
43、 systemIts origin is located in the northwest of Xian Yongle Town, referred to as the origin of Xian. Ellipsoid parameters are selected from the recommended values of the Sixteenth Congress of the 1975 International Union of Geodesy and geophysics. IUGG-75 ellipsoid parameter or IAG-75 earth ellipso
44、id for short. The coordinate system is often used in spatial data after 2000.New Beijing 1954 coordinate systemThe overall adjustment of the national geodetic network is adjusted to the J Lasovski ellipsoid, and a new coordinate system is formed, which is called the new Beijing coordinate system in
45、1954. The coordinate system is the same as the axis orientation datum of the national geodetic coordinate system in 1980, and the point accuracy of the network is the same.? WGS84 coordinate system (WGS, 84, Coordinate, System)In GPS positioning, the localization results belong to the WGS-84 coordin
46、ate system. The coordinate system is based on the use of higher precision VLBL, SLR and other results. The origin of the coordinate system is located in the center of mass of the earth, and the Z axis points to the BIH1984.0 polar region (CTP). The spatial data used in the GPS positioning system is
47、based on the coordinate system.Gauss-Kruger ProjectionProjection id=tmerc. Belong to the transverse Mercator projection. In order to control deformation, Chinas 1:2.5 million - 1:50 topographic maps are used 6 degrees belt, 1:1 million and larger scale topographic map using 3 degrees belt, to ensure
48、 the necessary accuracy. The 6 - degree belt is divided into 60 projection bands from Greenwich zero longitude line, each 6 degrees. The projection divides the area into two projection zones, which have been used as digital bases for topographic maps in many countries. From the 80 to the south latitude projection range within the 84 degree north latitude.The 3 - point zoning method is taken from 1