,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,两个模型矢量和栅格,栅格,基于格点的,矢量,基于坐标的,栅格数据,Represent the world surface into a regular grid of cells.,Raster data includes:,images,useful for storing and analyzing data that is continuous across an area.,Grids,栅格数据的表达,Real world,Grid,Point,Line,Area,Value,=0,=1,=2,=3,Row,Column,Triangles,Hexagons,RASTER,栅格数据的特点,形状,可以有多种形状，但是在实现中一般为正方形,各个栅格点大小一致,分辨率,栅格点大小越小，分辨率越高,取值方法,中心点法，平均值法，众数法,数值,反映了地表现象的空间分布属性，其属性可以是四种度量之一,栅格数据的编码,直接编码,数据量大,行程长度编码和块码,适合于存在较大斑块的栅格数据，否则不仅不能压缩，而且反而增大数据量,四叉树编码,思考：,栅格数据和图像很相似，是否可以采用如同JPEG的有损压缩方案,是否可以采用更高压缩效率的LZW存储栅格数据,块码和四叉树编码,矢量数据,Represent geographic phenomena with,Points,Lines,Polygons,Objects represented as nodes(X,Y points)and connecting lines,attributes of objects attached as database tables.,useful for representing and storing discrete features such as buildings,pipes,or parcel boundaries.,矢量数据的结构,Three basic vector data types,Points,Spatial objects with no area but can have attached attributes.,A single set of coordinates(X,Y)in a coordinate space.,Lines,Spatial object made up of connected points(nodes).,Have no width.,Polygons,Closed areas that can be made up of a circuit of line segments.,Line segments that make up a portion of a polygon.,(X,Y),(X2,Y2),(X3,Y3),(X4,Y4),(X5,Y5),Line,Point,(X5,Y5),(X,Y),(X2,Y2),(X4,Y4),(X3,Y3),Polygon,(X,Y),几何体的类型,矢量数据的特点,Spatial locations are explicit.,Relationships between entities/objects are implicit.,Vectors can store information about topology.,Much data comes in this form,Digitized mapping,Tracing and digitizing,Etc.,Best for features with discrete boundaries,Property lines,Political boundaries,Transportation,矢量数据的类型,Buildings.Polygon,Streams,Line,Wells,Point,Roads,Line,Zoning,Polygon,MAP SHEETS,在矢量存储中表达拓扑关系,三个表存储拓扑信息：,1、多边形,弧段,2、弧段点、多边形,3、节点/弧段,矢量数据和栅格数据的对比,从以下几个角度进行思考：,适合表达的地理对象,数据量,表达方式,实现难度,易于获得性,便于共享性,矢量和栅格的转换矢量,栅格,点和线地物,栅格,比较简单，只需要根据点或线的某个属性对相应栅格点进行赋值即可,矢量和栅格的转换矢量,栅格,多边形,需要进行填充，填充则要基于点和多边形的空间关系判断,扫描线算法（相切的情形需要区分）,4,3,4,1,2,2,矢量和栅格的转换矢量,栅格,基于拓扑多边形的边界代数算法,精品课件,！,精品课件,！,栅格到矢量的转换,将每个栅格点视为一个方形区域,因此，总是转换得到多边形地物,思路：区分不同的节点和边界类型（及2*2栅格区域内栅格数值的组合）,节点,边界点,