1、兩個(gè)模型矢量和柵格,柵格 基于格點(diǎn)的 矢量 基于坐標(biāo)的,柵格數(shù)據(jù),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,柵格數(shù)據(jù)的表達(dá),Real world,Grid,Point,Line,Area,Value,=0 =1 =2 =3,Row,Column,Triangles,Hexagons,RASTER,柵格數(shù)據(jù)的特

2、點(diǎn),形狀 可以有多種形狀，但是在實(shí)現(xiàn)中一般為正方形 各個(gè)柵格點(diǎn)大小一致 分辨率 柵格點(diǎn)大小越小，分辨率越高 取值方法 中心點(diǎn)法，平均值法，眾數(shù)法 數(shù)值 反映了地表現(xiàn)象的空間分布屬性，其屬性可以是四種度量之一,柵格數(shù)據(jù)的編碼,直接編碼 數(shù)據(jù)量大 行程長(zhǎng)度編碼和塊碼 適合于存在較大斑塊的柵格數(shù)據(jù)，否則不僅不能壓縮，而且反而增大數(shù)據(jù)量 四叉樹(shù)編碼 思考： 柵格數(shù)據(jù)和圖像很相似，是否可以采用如同JPEG的有損壓縮方案 是否可以采用更高壓縮效率的LZW存儲(chǔ)柵格數(shù)據(jù),塊碼和四叉樹(shù)編碼,矢量數(shù)據(jù),Represent geographic phenomena with Points Lines Polygon

3、s 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.,矢量數(shù)據(jù)的結(jié)構(gòu),Three basic vector data types Points Spatial objects with no area but can

4、 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.,幾何體的類(lèi)型,矢量數(shù)據(jù)的特點(diǎn),Spa

5、tial 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,矢量數(shù)據(jù)的類(lèi)型,在矢量存儲(chǔ)中表達(dá)拓?fù)潢P(guān)系,三個(gè)表存儲(chǔ)拓?fù)湫畔ⅲ?1、多邊形弧段 2、弧段點(diǎn)、多邊形 3、節(jié)點(diǎn)/弧段,矢量數(shù)據(jù)和柵格數(shù)據(jù)的對(duì)比,從以下幾個(gè)角度進(jìn)行思考： 適合表達(dá)的地理對(duì)象 數(shù)據(jù)量 表達(dá)方式 實(shí)現(xiàn)難度 易于獲得性 便于共享性 ,矢量和柵格的轉(zhuǎn)換矢量柵格,點(diǎn)和線地物柵格 比較簡(jiǎn)單，只需要根據(jù)點(diǎn)或線的某個(gè)屬性對(duì)相應(yīng)柵格點(diǎn)進(jìn)行賦值即可,矢量和柵格的轉(zhuǎn)換矢量柵格,多邊形 需要進(jìn)行填充，填充則要基于點(diǎn)和多邊形的空間關(guān)系判斷 掃描線算法（相切的情形需要區(qū)分）,4,3,4,1,2,2,矢量和柵格的轉(zhuǎn)換矢量柵格,基于拓?fù)涠噙呅蔚倪吔绱鷶?shù)算法