Chapter 3 Vector Data Model Power Point by
Chapter 3 Vector Data Model 矢量数据模型 浙江水利水电专科学校 Power. Point by 1 僧德文
CHAPTER 3: VECTOR DATA MODEL 第 3 章 矢量数据模型 • • 3. 1 Georelational data model 地理关系数据模型 3. 2 Representation of Simple Features 简单要素的表示 3. 3 Topology 拓扑 • 3. 4 Nontopological Vector Data 非拓扑矢量数据 • 3. 5 Data Models for Composite Features 复合要素数据模型 2
How does a computer “see” map features? 计算机如何“看”地图要素？ • Vector data model 矢量数据模型 – Uses x, y coordinates of points to represent points, lines, areas 用点的 x, y 坐标来代表点、线、面 – Organizes geometric objects thus represented into digital data files 将如此表示的几何对象组织成数字化数据文件 3
Evolution of Vector Data Model 矢量数据模型的演变 • ESRI, Inc. – Arc/Info: coverages – Arc. View: shapefiles – Arc. GIS: geodatabase 4 地理相关数据模型 基于对象数据模型
3. 1 Georelational Data Model 地理相关数据模型 • Geographically referenced data: 地理参照数据： – Spatial and attribute components • 空间和属性组分 Georelational data model 地理相关数据模型 – Stores spatial and attribute data separately with a link in a split system 空间数据和属性数据分别贮存在链接的分离系统 – Called relational database 所谓关系数据库 • Object-based data model stores spatial and attribute data together, not a split system 基于对象数据模型将空间数据和属性数据贮存在一起 5
Figure 3. 2 Based on the georelational data model, an Arc. Info coverage has two components: graphic files for spatial data and INFO files for attribute data. The label connects the two components. 6
3. 2 Representation of Simple Features 简单要素的表示 • Vector data model 矢量数据模型 – Uses geometric objects of point, line, area to represent spatial features – 用点、线、面等几何对象表示空间要素 Figure 3. 3 Point, line, and area features. 7
Point • • • Zero dimensions No length, width or height, only location implied Defined by x, y coordinates Also called a node or vertex Examples: wells, buildings, survey markers 例如：井、建筑物、测量标记 8
Line • • • One-dimensional Properties of length and location Defined by x, y coordinates of its end points and (if curved) of points along its path Lines also known as edges, links Examples: roads, streams, contour lines 例如：道路、河流、等高线 9
Area • • • Two-dimensional (length and width) Properties of area and perimeter Defined by its boundary line (which is defined by its points) Also called polygon Examples: political entities, water bodies 例如：行政区、水体 10
Map Scale 地图比例尺 • Representation of map features dependent on map scale 地图要素的表示取决于地图比例尺 • A city at 1: 1, 000 may appear as a point, but at 1: 24, 000 it will be an area 一个城市在 1: 1, 000 地图以一点出现，在 1: 24, 000 则为一个区域 • 11 Government mapping standards 政府制图标准
3. 3 Topology 拓扑 • Explicit expression of spatial relationship between features 要素空间关系的清晰表达 • Graph theory – Directed lines – arcs 弧段 – Nodes - points where arcs meet or intersect 结点 - 弧段会合点或交叉点 12
13 Figure 3. 4 The adjacency matrix and incidence matrix for a digraph.
3. 3. 1 TIGER • Topologically Integrated Geographic Encoding and Referencing 拓扑综合地理编码参照格式 • U. S. Census Bureau database 美国人口普查局数据库 • 14 Defined spatial relationships between points, lines, and areas 在点、线、面之间定义空间关系
15 Figure 3. 5 Topology in the TIGER database involves 0 -cells or points, 1 -cells or lines, and 2 -cells or areas.
Figure 3. 6 Address ranges and zip codes in the TIGER database have the right- or left-side designation based on the direction of the street. 16
3. 3. 2 ESRI’s Coverage Model • • Model introduced in the 1980 s to separate CAD from GIS Supports three basic topological relationships – Connectivity 联通性 – Area definition 面积定义 – Contiguity 邻接性 17
3. 3. 3 Coverage Data Structure • Incorporates topological relationships into data structure 使拓扑关系与数据结构一体化 • Contains feature IDs and x-y coordinate pairs 含要素标识号和 x-y 坐标对 18
Figure 3. 7 The data structure of a point coverage. 19
Figure 3. 8 The data structure of a line coverage. 20
21 Figure 3. 9 The data structure of a polygon coverage.
3. 3. 4 Importance of Topology 拓扑重要性 • Assurance of data quality 保障数据质量 – Error detection 查错 • Enhance GIS analysis 增强GIS 分析 – Networks (streets, utilities) 网络（街道、设施） 22
23 Figure 3. 10 A polygon coverage, shown in a, has topological errors. Each small square symbol represents an error caused by lines that do not meet correctly. The shapefile, shown in b, is converted from the polygon coverage.
3. 4 Nontopological Vector Data 非拓扑矢量数据 • • Common option among GIS software vendors GIS软件商的共同选择 Shapefile (ESRI) – Duplicate arcs for shared boundaries 共享边界有两重弧段 – Can be converted to coverages and vice versa 与 coverages 可相互转换 24
Advantages of Nontopological Vector Data 非拓扑矢量数据的优点 • Can display more rapidly on monitors 在监视器上显示更快 – Important for users rather than producers of databases 对用户比对数据库制作者更为重要 • Nonproprietary and interoperable 非私有，可共用 – Can be used across software packages 可跨软件使用 25
3. 5 Data Models for Composite Features 复合要素数据模型 • Features represented as composites of points, lines, and areas 要素以点、线、面的复合体表示 26
3. 5. 1 TIN • Triangulated irregular network 不规则三角网 • Approximates terrain with a set of non-overlapping triangles 用一系列不叠置三角形近似表示地形 – Irregularly sampled elevation data 不规则采样的高程数据 – Delaunay triangulation 德老内三角测量 – Roads, streams, lakes, etc. added 加上道路、河流、湖泊 等 27
28 Figure 3. 11 A TIN uses a series of non-overlapping triangles to approximate the terrain.
Figure 3. 12 The data structure of a TIN. 29
3. 5. 2 Regions 分区 • • A geographic area with similar characteristics 具有类似特征的地理范围 Hierarchical regions 有等级的分区 – Progressively smaller subregions of increasingly uniform characteristics 随亚区趋于变小，其均一特征递增 30
Data Model for Regions 分区数据模型 • Able to handle overlapping and spatially disjoint polygons 可叠置； 空间不连续 31 Figure 3. 14 The regions data model allows overlapped regions (a) and spatially disjoint components (b).
32 Figure 3. 13 A hierarchy of counties and states in the conterminous United States.
Regions Data Model 分区数据模型 • Becoming obsolete 趋于陈旧 • New data formats solve the problems 新的数据格式解决问题 33
3. 5. 3 Routes 路径 • Linear features 线状要素 • Measurement system 测量系统 • Transportation agencies and companies 交通机构和公司 34
35 Figure 3. 16 The data structure of a route subclass.
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