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我想根据高程将多边形图层切割成两部分（上部和下部）。多边形可能是凸面或凹面，切割的位置可能会有所不同。等高线的间隔为 5m，这意味着我可能需要生成一个具有很多浓缩等高线的等高线，例如 1m 间隔。关于如何在 ArcGIS 或 R 中更好地做到这一点的任何想法？下面是 Q 的运行示例：

library(sp)
library(raster)
r<-raster(ncol=100,nrow=100)
values(r)<-rep(1:100,100)
plot(r)   ### I have no idea why half of the value is negative...
p1<-cbind(c(-100,-90,-50,-100),c(60,70,30,30,60))
p2<-cbind(c(0,50,100,0),c(0,-25,10,0))
p1p<-Polygons(list(Polygon(p1,hole=T)),"p1")
p2p<-Polygons(list(Polygon(p2,hole=T)),"p2")
p<-SpatialPolygons(list(p1p,p2p),1:2)
plot(p,add=T)
segments(-90,80,-90,20)  ##where the polygon could be devided
segments(50,20,50,-30)  ##

先谢谢了~

马可

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1 回答 1

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如果我理解正确，您可以使用rgeosR 中的包和相关的空间工具。

我采取了缓冲相交线的技巧，然后从该站点生成“差异”多边形：

http://www.chopshopgeo.com/blog/?p=89

生成示例栅格和上覆多边形。

vdata <- list(x = 1:nrow(volcano), y = 1:ncol(volcano), z = volcano)

## raw polygon data created using image(vdata); xy <- locator()

xy <- structure(list(x = c(43.4965355534823, 41.7658494766076, 36.2591210501883, 
25.560334393145, 13.7602020508178, 18.7949251835441, 29.179041644792, 
40.6645037913237, 44.2832110429707, 47.272577903027, 47.5872480988224
), y = c(30.0641086410103, 34.1278207016757, 37.6989616034726, 
40.900674136118, 32.7732500147872, 27.4781100569505, 22.5523984682652, 
22.7986840476995, 24.5226831037393, 29.3252519027075, 33.8815351222414
)), .Names = c("x", "y"))

## close the polygon
coords <- cbind(xy$x, xy$y)
coords <- rbind(coords, coords[1,])

library(sp)

## create a Spatial polygons object
poly <- SpatialPolygons(list(Polygons(list(Polygon(coords, hole = FALSE)), "1")))


## create a contour line that cuts the polygon at height 171
cl <- contourLines(vdata, levels = 171)

## for ContourLines2SLDF
library(maptools)

clines <- ContourLines2SLDF(cl)

现在，将多边形与线相交，然后稍微缓冲线并再次与多边形不同以给出多部分多边形。

library(rgeos)
lpi <- gIntersection(poly, clines)

blpi <- gBuffer(lpi, width = 0.000001)

dpi <- gDifference(poly, blpi)

绘制原始数据，并从 Spatial 对象中手动提取一半的多边形。

par(mfrow = c(2,1))

image(vdata)
plot(poly, add = TRUE)

plot(SpatialPolygons(list(Polygons(list(dpi@polygons[[1]]@Polygons[[1]]), "1"))), 
     add = TRUE, col = "lightblue")

image(vdata)
plot(poly, add = TRUE)
cl <- contourLines(vdata, levels = 171)

plot(SpatialPolygons(list(Polygons(list(dpi@polygons[[1]]@Polygons[[2]]), "2"))), 
     add = TRUE, col = "lightgreen")

这适用于这个相当简单的案例，它可能对您的场景有用。

于 2011-05-03T05:54:51.523 回答