从分布的点集创建多边形

Question

我需要 R 语言方面的帮助

来自我的代码：

inter1= read.table("C:/inter.csv", header=TRUE)
inter1$xx<-inter1$long
inter1$yy<-inter1$lat
coordinates(inter1) = ~long + lat
#Plot the results:
plot(inter1)

我有这个情节：http://i.stack.imgur.com/98aTf.png

我现在正在寻找绘图上的每组点绘制一个多边形，我不知道我必须经过什么过程才能到达那里，谢谢你的帮助

inter.csv：

long    lat var1.pred
1   4.2 19  31.8216045615229
2   4.3 19  31.913824396486
3   4.4 19  32.0090783396173
4   4.5 19  32.1067681024233
5   4.6 19  32.2061094352961
6   4.7 19  32.3061148156713
7   4.8 19  32.4055837134796
8   4.9 19  32.503104196147
9   5   19  32.5970697606984
10  5.1 19  32.6857147918646
11  5.2 19  32.767170733855
12  5.3 19  32.8395428348418
13  5.4 19  32.9010042955024
14  5.5 19  32.9499012300441
15  5.6 19  32.9848587133105
16  5.7 19  33.004876178167
17  5.8 19  33.0094002932703
18  5.9 19  32.998365567474
19  6   19  32.9721970820907
20  6.1 19  32.9317751315546
21  6.2 19  32.8783669584517
22  6.3 19  32.8135349988031
23  6.4 19  32.7390332831422
24  6.5 19  32.6567036402505

Answer 1

在您的情况下，一种解决方案是通过中间光栅化，然后将其多边形化。可以平滑多边形以获得更好的可视化效果。见下方代码

inter1= read.table("inter.csv", header=TRUE)

#add a category (required for later rasterizing/polygonizing)
inter1 <- cbind(inter1, cat = rep(1L, nrow(inter1)),stringsAsFactors = FALSE)

#convert to spatial points
coordinates(inter1) = ~long + lat

#gridify your set of points
gridded(inter1) <- TRUE

#convert to raster
r <- raster(inter1)

#convert raster to polygons
sp = rasterToPolygons(r, dissolve = T)

#addition transformation to distinguish well the set of polygons
polys <- slot(sp@polygons[[1]], "Polygons")
output <- SpatialPolygons(
  Srl = lapply(1:length(polys),
               function(x){
                 p <- polys[[x]]

                 #applying spline.poly function for smoothing polygon edges
                 px <- slot(polys[[x]], "coords")[,1]
                 py <- slot(polys[[x]], "coords")[,2]
                 bz <- spline.poly(slot(polys[[x]], "coords"),100, k=3)
                 bz <- rbind(bz, bz[1,])
                 slot(p, "coords") <- bz               

                 # create Polygons object
                 poly <- Polygons(list(p), ID = x)
                 return(poly)
               }),
  proj4string = CRS("+init=epsg:4326")
)

#plot
plot(sp, border = "gray", lwd = 2) #polygonize result
plot(output, border = "red",  add = TRUE) #smoothed polygons

注意：您有长/纬度坐标 (crs = EPSG:4326)，所以我制作了这个示例，以便您可以在构建过程中查看在何处指定空间多边形的投影。如果此时没有指定proj4string，在创建output对象做proj4string(output) <- CRS("+init=epsg:4326")之后仍然可以这样做