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栅格和矢量数据

栅格和矢量数据. 栅格和矢量数据的特点 编码方式 转换方法. 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. RASTER. 栅格数据的表达. Point. Line. Column.

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栅格和矢量数据

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  1. 栅格和矢量数据 栅格和矢量数据的特点 编码方式 转换方法

  2. 两个模型——矢量和栅格 • 栅格 • 基于格点的 • 矢量 • 基于坐标的

  3. 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

  4. RASTER 栅格数据的表达 Point Line Column Real world Value Row =0 =1 =2 =3 Grid Area Triangles Hexagons

  5. 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

  6. 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

  7. 块码和四叉树编码

  8. 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.

  9. Point (X,Y) (X2,Y2) Line (X4,Y4) (X3,Y3) (X5,Y5) (X,Y) (X,Y) (X2,Y2) Polygon (X5,Y5) (X3,Y3) (X4,Y4) 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.

  10. 几何体的类型

  11. 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

  12. MAP SHEETS Zoning, Polygon Streams, Line Wells, Point Roads, Line Buildings. Polygon 矢量数据的类型

  13. 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

  14. 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 • …

  15. 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

  16. 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

  17. 基于拓扑多边形的边界代数算法 矢量和栅格的转换——矢量栅格

  18. 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） 边界点 节点

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