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Chapter 2

Chapter 2. Coordinate Systems 坐 标 系 统. 浙江水利水电专科学校 PowerPoint by 僧德文. CHAPTER 2: Coordinate Systems 坐标系统. Chapter Outline 概要 2.1 Geographic Coordinate System 地理坐标系统 2.2 Map Projections 地图投影 2.3 Commonly Used Map Projections 常用地图投影 2.4 Projected Coordinate Systems 投影坐标系统

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Chapter 2

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  1. Chapter 2 Coordinate Systems 坐 标 系 统 浙江水利水电专科学校 PowerPoint by 僧德文

  2. CHAPTER 2:Coordinate Systems 坐标系统 • Chapter Outline 概要 • 2.1 Geographic Coordinate System 地理坐标系统 • 2.2 Map Projections 地图投影 • 2.3 Commonly Used Map Projections 常用地图投影 • 2.4 Projected Coordinate Systems 投影坐标系统 • 2.5 Working with Coordinate Systems in GIS 在GIS中使用坐标系统

  3. Basic Principle基本原理 • Map layers must align spatially 地图必须以空间排列 • Concept of registration 注册的概念

  4. Figure 2.1 The top map shows the road networks in Idaho and Montana based on different coordinate systems. The bottom map shows the road networks based on the same coordinate system.

  5. 2D versus 3D • Maps are two-dimensional 地图是二维的 • Map feature location identified with x- and y-coordinates 地图要素位置以 x 和 y 坐标值识别 • Earth’s surface is three-dimensional 地球表面是三维的 • Feature location expressed in latitude and longitude 要素位置以经纬度表达 • How do we register the three-dimensional Earth to the two-dimensional map? 如何把三维的地球注册成二维的地图？ • How do we register data that comes in different coordinate systems? 如何注册不同坐标系统的数据？

  6. 2.1 Geographic Coordinate System地理坐标系统 • Location reference system for spatial features on earth’s surface 作为地球表面空间要素的位置参照系统 • Angular measurement from an origin to a given point 由原点到特定点的角度测量 • Latitude (parallels) 纬线 • Longitude (meridians) 经线 • Measured in DMS, DD, or radians 以“度分秒”、“10进制度”或“弧度”为量纲

  7. Figure 2.2 The geographic coordinate system.

  8. Figure 2.3 A longitude reading is represented by a on the left, and a latitude reading is represented by b on the right. Both longitude and latitude readings are angular measures.

  9. 2.1.1 Approximation of the Earth地球的近似表示 • Shape of Earth not perfectly circular • Spheroid (ellipsoid) 椭球体 • Major axis (a) • Minor axis (b) • Flattening (f) 扁率 • (a-b)/a • Geographic coordinates 地理坐标 Figure 2.4 The flattening is based on the difference between the semimajor axis a and the semiminor axis b.

  10. 2.1.2 Datum 大地水准面 • Mathematical model of Earth 地球的数学模型 • Serves as reference for calculating geographic coordinates • Definition of a datum 大地水准面的定义 • origin 坐标原点 • parameters of spheroid 椭球参数 • separation of earth from spheroid at origin 地球与椭球原点的偏离

  11. 2.1.2 Datum 大地水准面 • Clarke 1866 • NAD 27 • NAD 83 • GRS 80 • WGS 84 • Local datums 地方基准 • Significance of datum choice 选择基准的意义 我国1980年后采用“1975年大地坐标系（IAG/IUGG)”

  12. 2.2 Map Projections 地图投影 • Conversion (projection) from round Earth (3D) to flat map (2D) 从圆的地球到平的地图的转换 • Inherent distortions in the process 投影过程的固有变形 • Size, shape, distance, direction 大小、形状、距离、方向 • We can preserve one or two of these properties at the expense of the others 可保持其中一两种性质不变而以牺牲其他性质为代价

  13. 2.2.1 Projection Types 投影类型 • Conformal (true shape) 等角 • Equivalent (equal area) 等积 • Equidistant 等距 • Azimuthal or true direction 方位角或真方向 • Conformal and equivalent mutually exclusive 等角与等积相互排斥

  14. 2.2.1 Projection Types • Reference globe 参考球体 • Cylindrical 圆柱的 • Conic 圆锥的 • Azimuthal (planar) 方位角的（平面的） • Hybrid 混合的

  15. Case情景 Figure 2.6 Case and projection.

  16. Aspect朝向 Figure 2.7 Aspect and projection.

  17. 2.2.2 Map Projection Parameters地图投影参数 • Standard line or point 标准线或点 • Standard parallel 标准纬线 • Standard meridian 标准经线 • Principal scale 主比例尺 • Scale factor 比例因子

  18. Figure 2.8 The central meridian （b) in this secant case transverse Mercator projection has a scale factor of 0.9996. The two standard lines on either side of the central meridian have a scale factor of 1.0.

  19. 2.3 Commonly Used Map Projections常用地图投影（中国） 地图投影的选择主要考虑地图的用途、比例尺、区域形状与大小、地理位置及其他特殊要求。 2.3.1 正轴等面积割圆锥投影 常用于行政区划图及其他要求无面积变形的地图（如：土地利用图、森林分布图等）。地图出版社出版的中国全图、省区行政区划图均采用之。

  20. 2.3.2 正轴等角割圆锥投影 标准纬线上无变形，要在图上量测长度和面积，必须进行纠正。 常用于我国的地势图与各种气象、气候图，以及各省区的地势图。

  21. 2.3.3 横切等角椭圆柱投影（高斯-克吕格投影） 该投影是以经差6度或3度为一带投影到椭圆柱面上，然后展开成平面的。中央经线长度不变，其他经线最大长度变形达＋0.14%，最大面积变形达＋0.27%。在这种图上进行量测精度较高。我国1:5000到1:50万比例尺地形图均采用此投影。

  22. 2.3 Commonly Used Map Projections（美国） 2.3.1 Transverse Mercator 2.3.2 Lambert Conformal Conic 2.3.3 Albers Equal-Area Conic 2.3.4 Equidistant Conic

  23. Figure 2.10 The Mercator and the transverse Mercator projection of the United States. For both projections, the central meridian is 90°W and the latitude of true scale is the equator.

  24. Figure 2.11 The Lambert conformal conic projection of the conterminous United States. The central meridian is 96°W, the two standard parallels are 33°N and 45°N, and the latitude of projection’s origin is 39°N.

  25. 2.4 Projected Coordinate Systems投影坐标系统 • Also called plane coordinate system 平面坐标系统 • Built on specific map projections 建立在特定地图投影上 • Designed for detailed calculations and positioning 为详细计算和定位而设计 • Based on two-dimensional cartesian space (x, y coordinates) 基于二维迪卡尔空间（x、y坐标）

  26. 伪原点 Figure 2.9 The central parallel and the central meridian divide a map projection into four quadrants. Points within the NE quadrant have positive x- and y-coordinates, points within the NW quadrant have negative x-coordinates and positive y-coordinates, points within the SE quadrant have positive x-coordinates and negative y-coordinates, and points within the SW quadrant have negative x- and y-coordinates. The purpose of having a false origin is to place all points within the NE quadrant.

  27. 2.4.1 Universal Transverse Mercator (UTM) Grid System 2.4.2 Universal Polar Stereographic (UPS) Grid System 2.4.3 State Plane Coordinate (SPC) System 2.4.4 Public Land Survey System (PLSS)

  28. Figure 2.12 UTM zones range from zone 10N to 19N in the conterminous United States.

  29. Figure 2.13 A UTM zone represents a secant case transverse Mercator projection. CM is the central meridian, and AB and DE are the standard meridians. The standard meridians are placed 180 kilometers west and east of the central meridian. Each UTM zone covers 6° of longitude and extends from 84°N to 80°S. The size and shape of the UTM zone are exaggerated for illustration purposes.

  30. Figure 2.14 SPC83 zones in the conterminous United States. The thinner lines are county boundaries, and the gray lines are state boundaries. This map corresponds to the SPC83 table on the inside of this book’s back cover.

  31. Figure 2.15 The shaded survey township has the designation of T1S, R2E. T1S means that the survey township is south of the base line by one unit. R2E means that the survey township is east of the Boise (principal) meridian by 2 units. Each survey township is divided into 36 sections. Each section measures 1 mile by 1 mile and has a numeric designation.

  32. 2.5 Working with Coordinate Systems in GIS 在GIS中使用坐标系统 • Precisely establishing location 准确建立位置 • Registration 注册 2.5.1 Projection File 投影文件 2.5.2 Predefined Coordinate Systems 预定义坐标系统 2.5.3 On-the-Fly Projection 快速投影

  33. 2.5.1 Projection File 投影文件 • Text file that stores information on the coordinate system on which the data set is based 储存数据所依据的坐标系统信息的文本

  34. 2.5.2 Predefined Coordinate Systems预定义坐标系统 • GIS package groups coordinate systems into predefined and custom GIS 软件包把坐标系统分为预定义的和自定义的 • Predefined means that parameter values are known and already coded into the GIS package 预定义是指参数取值是已知的，并编码到GIS软件包

  35. 2.5.3 On-the-Fly Projection 快速投影 • Designed for displaying data sets based on different coordinate systems 为显示基于不同坐标系统的数据集而设计 • Automatically converts data sets to a common coordinate system 自动将数据集转换成共同的坐标系统 实质上是两个平面场之间点的坐标变换（基于两种地图投影点坐标的关系式）

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