R 从 SpatialPointsDataFrame 到 SpatialLines

Question

我有一个 SpatialPointsDataFrame 加载与

pst<-readOGR("/data_spatial/coast/","points_coast")

我想在输出中获得 SpatialLines，我找到了一些东西

coord<-as.data.frame(coordinates(pst))
Slo1<-Line(coord)

Sli1<-Lines(list(Slo1),ID="coastLine")
coastline <- SpatialLines(list(Sli1))
class(coastline)

它似乎有效，但是当我尝试 plot(coastline) 时，我有一条不应该存在的线......

有人可以帮助我吗？ The shapefile is here！

Answer 1

我查看了 shapefile。有一个id 列，但是如果您绘制数据，似乎id 没有按南北顺序排列。创建额外的线是因为点顺序不完美，连接表中彼此相邻但在空间方面彼此相距较远的点。您可以通过计算点之间的距离然后按距离排序来尝试找出数据的正确排序。

一种解决方法是删除那些长于一定距离的线条，例如500 m..首先，找出连续坐标之间的距离大于这个距离：breaks。然后取两个breaks 之间的坐标子集，最后为该子集创建线。您最终会得到一条由多个 (breaks-1) 段组成且没有错误段的海岸线。

# read data
library(rgdal)
pst<-readOGR("/data_spatial/coast/","points_coast")
coord<-as.data.frame(coordinates(pst))
colnames(coord) <- c('X','Y')

# determine distance between consective coordinates
linelength = LineLength(as.matrix(coord),sum=F)
# 'id' of long lines, plus first and last item of dataset
breaks = c(1,which(linelength>500),nrow(coord))

# check position of breaks
breaks = c(1,which(linelength>500),nrow(coord))

# plot extent of coords and check breaks
plot(coord,type='n')
points(coord[breaks,], pch=16,cex=1)

# create vector to be filled with lines of each subset
ll <- vector("list", length(breaks)-1)
for (i in 1: (length(breaks)-1)){
    subcoord = coord[(breaks[i]+1):(breaks[i+1]),]

# check if subset contains more than 2 coordinates
    if (nrow(subcoord) >= 2){
        Slo1<-Line(subcoord)
        Sli1<-Lines(list(Slo1),ID=paste0('section',i))
        ll[[i]] = Sli1
    }

}

# remove any invalid lines
nulls = which(unlist(lapply(ll,is.null)))
ll = ll[-nulls]
lin = SpatialLines(ll)
# add result to plot
lines(lin,col=2)

# write shapefile
df = data.frame(row.names=names(lin),id=1:length(names(lin)))
lin2 = SpatialLinesDataFrame(sl=lin, data=df)
proj4string(lin2) <- proj4string(pst)
writeOGR(obj=lin2, layer='coastline', dsn='/data_spatial/coast', driver='ESRI Shapefile')