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1、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 Sys
2、tems 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.
3、,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 Earths 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-dimensi
4、onal 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 earths 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 La
5、titude (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 r
6、eadings 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
7、 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 186
8、6 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
9、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,1
10、4,2.2.1 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 Stan
11、dard 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 Project
12、ions 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%
13、，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
14、 both projections, the central meridian is 90W 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 96W, the two standard parallels are 33N and 45N, and the latitude of projections origin is 39
15、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,Figure 2.9 The central para
16、llel 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.,
