我需要一次测试（即TRUE / FALSE）一对，SpatialLinesDataFrame元素是否与SpatialPolygonsDataFrame元素相交。如果为TRUE，则删除每个多边形中与每条线相交的部分（一次每条），然后保存到新列表中。
多边形存储在多功能SpatialPolygonsDataFrame中，线存储在单个SpatialLinesDataFrames的列表中。我创建了一个嵌套循环来遍历每个多边形和线元素。我正在使用raster::intersect，raster::extent和raster::erase函数。
library(sp)
library(raster)
#create multi-feature SpatialPolygonDataFrame
p <-
SpatialPolygons(list(Polygons(list(Polygon(cbind(c(2,4,3,2),c(2,2,4,2)))),
"1"),
Polygons(list(Polygon(cbind(c(12,14,13,12),c(0,0,2,0)))), "2"),
Polygons(list(Polygon(cbind(c(25,24,22,25),c(22,23,22,22)))), "3"),
Polygons(list(Polygon(cbind(c(0,2,1,0),c(12,12,14,12)))), "4"),
Polygons(list(Polygon(cbind(c(5,7,6,5),c(5,5,7,5)))), "5")))
# Create a dataframe and display default rownames
p.df <- data.frame( ID=1:length(p))
rownames(p.df)
# Extract polygon ID's
pid <- sapply(slot(p, "polygons"), function(x) slot(x, "ID"))
# Create dataframe with correct rownames
p.df <- data.frame( ID=1:length(p), row.names = pid)
# coersion
p <- SpatialPolygonsDataFrame(p, p.df)
#create list of single-feature SpatialLineDataFrame
l1 <- cbind(c(0,3), c(0,3))
l2 <- cbind(c(0, 13), c(0, 1))
l3 <- cbind(c(0, 24), c(0,22.5))
l4 <- cbind(c(0, 1), c(0,13))
l5 <- cbind(c(0, 6), c(0,6))
Sl1 <- Line(l1)
Sl2 <- Line(l2)
Sl3 <- Line(l3)
Sl4 <- Line(l4)
Sl5 <- Line(l5)
Sl1 <- Lines(list(Sl1), ID = "1")
Sl2 <- Lines(list(Sl2), ID = "2")
Sl3 <- Lines(list(Sl3), ID = "3")
Sl4 <- Lines(list(Sl4), ID = "4")
Sl5 <- Lines(list(Sl5), ID = "5")
Sl <- SpatialLines(list(Sl1, Sl2, Sl3, Sl4, Sl5))
# Create a dataframe and display default rownames
Sl.df <- data.frame( ID=1:length(Sl))
rownames(Sl.df)
# Extract polygon ID's
pidl <- sapply(slot(Sl, "lines"), function(x) slot(x, "ID"))
# Create dataframe with correct rownames
Sl.df <- data.frame( ID=1:length(Sl), row.names = pidl)
# coersion
Sldf <- SpatialLinesDataFrame(Sl, Sl.df)
#convert multipart SpatialLineDataFrame feature to individual features in
list
linel <- list()
linel[[1]] <- Sldf[1,]
linel[[2]] <- Sldf[2,]
linel[[3]] <- Sldf[3,]
linel[[4]] <- Sldf[4,]
linel[[5]] <- Sldf[5,]
#if a line intersects with a polygon, erase part of line where polygon
#overlaps, save to new list, and add original line ID + ID of intersected
#polygon
list1 <- list()
index=0
for (i in 1:length(linel)) {
for (j in 1:length(p)) {
if (!is.null(raster::intersect(extent(p[j,]), linel[[i]]))) {
index=index+1
list1[[index]] <- erase(linel[[i]],p[j,])
list1[[index]]@data["id.parent"] <- linel[[i]]@data$ID
#add intersected polygon ID to the line attribute table
list1[[index]]@data["id.intersect"] <- p[j,]@data$ID
}}}
list1
#check results by plotting
plot(p)
plot(list1[[1]], add=T) #parent 1-1
plot(list1[[2]], add=T) #parent 2-2
plot(list1[[3]], add=T) #parent-intersect 3-1
plot(list1[[4]], add=T) #??? p-i 3-2 BUT DOES NOT INTERSECT WITH p[2,]!
plot(list1[[5]], add=T) #parent 3-3
plot(list1[[6]], add=T) #???? p-i 3-4 BUT DOES NOT INTERSECT WITH p[4,]!
plot(list1[[7]], add=T) #p-i 3-5
plot(list1[[8]], add=T) #parent 4-4
plot(list1[[9]], add=T) #p-i 5-1
plot(list1[[10]], add=T) #parent 5-5
#test raster::intersect function on linel[[3]] based on plotted errors
#above:
!is.null(raster::intersect(extent(p[1,]), linel[[3]]))
#output = 'TRUE' (correct)
!is.null(raster::intersect(extent(p[2,]), linel[[3]]))
#output = 'TRUE' (INCORRECT)
!is.null(raster::intersect(extent(p[3,]), linel[[3]]))
#output = 'TRUE' (correct)
!is.null(raster::intersect(extent(p[4,]), linel[[3]]))
#output = 'TRUE' (INCORRECT)
!is.null(raster::intersect(extent(p[5,]), linel[[3]]))
#output = 'TRUE' (correct)
大多数结果与预期的一样，但是一些raster::intersect布尔结果不正确；也就是说，他们说多边形与线不相交。为什么会这样？
答案 0 :(得分：1)
这是创建这些对象的简化方法
library(raster)
p1 <- cbind(c(2,4,3,2),c(2,2,4,2))
p2 <- cbind(c(12,14,13,12),c(0,0,2,0))
p3 <- cbind(c(25,24,22,25),c(22,23,22,22))
p4 <- cbind(c(0,2,1,0),c(12,12,14,12))
p5 <- cbind(c(5,7,6,5),c(5,5,7,5))
p <- spPolygons(p1, p2, p3, p4, p5, attr=data.frame(polID=1:5))
#create list of single-feature SpatialLineDataFrame
l1 <- cbind(c(0,3), c(0,3))
l2 <- cbind(c(0, 13), c(0, 1))
l3 <- cbind(c(0, 24), c(0,22.5))
l4 <- cbind(c(0, 1), c(0,13))
l5 <- cbind(c(0, 6), c(0,6))
Sldf <- spLines(l1, l2, l3, l4, l5, attr=data.frame(lineID=1:5))
#linel <- lapply(1:5, function(i) Sldf[i,])
为什么不一步一步做到这一点？
x <- intersect(Sldf, p)
plot(x)
data.frame(x)
# lineID polID
#1 1 1
#2 2 2
#3 3 1
#4 3 3
#5 3 5
#6 4 4
#7 5 1
#8 5 5
您可以获得类似的结果：
result <- list()
index <- 1
for (i in 1:length(Sldf)) {
for (j in 1:length(p)) {
if (is.null(raster::intersect(extent(p[j,]), extent(Sldf[i, ])))) next
#if (is.null(raster::intersect(p[j,], Sldf[i, ]))) next
if (!rgeos::gIntersects(p[j,], Sldf[i, ])) next
e <- erase(Sldf[i,], p[j,])
e$polID <- p[j,]$polID
result[[index]] <- e
index <- index + 1
}}
t(sapply(result, data.frame))
# lineID polID
#[1,] 1 1
#[2,] 2 2
#[3,] 3 1
#[4,] 3 3
#[5,] 3 5
#[6,] 4 4
#[7,] 5 1
#[8,] 5 5
请注意，与您的代码的不同之处在于，您无需检查多边形是否与直线相交。您仅检查它是否与直线范围相交。可以快速检查一下，但不足以满足您的目的。