如何获得多个多边形的交集？

Question

我有一个'SpatialPolygonsDataFrame'列表，我想接收所有这些多边形的交集。我已经在stackoverflow.com上找到了一些如何解决此问题的提示，但是，我想知道为什么收到此错误消息。

请参阅 网址：https://gis.stackexchange.com/questions/140504/extracting-intersection-areas-in-r 网址：https://gis.stackexchange.com/questions/156660/loop-to-check-multiple-polygons-overlap-in-r

length_b_loop <- length(as.vector(dat_ftprints))-1
# dat_ftprints is the list of 25 SpatialPolygonsDataFrame

for (b in length_b_loop){
  if (b == 1){
    spc_intersect_poly1 <- dat_ftprints[[b]]
    spc_intersect_poly2 <- dat_ftprints[[b+1]]
    spc_intersect_temp <- raster::intersect(spc_intersect_poly1, spc_intersect_poly2)
  } else {
    spc_intersect_poly3 <- dat_ftprints[[b+1]]
    spc_intersect_temp <- raster::intersect(spc_intersect_temp, spc_intersect_poly3)
  }
}
# get a single polygon which represents the intersection of all polygons stored in the list

错误消息：

  

xy.coords（x，y，xlabel，ylabel，log）中的错误：        “ x”是一个列表，但没有组件“ x”和“ y”

非常感谢！

Answer 1

我无法确认这一点，因为您没有提供可重复的示例，但是您的for循环中似乎有错误。您仅在值24而不是值1到24上进行迭代。这意味着未正确创建spc_intersect_temp，并且仍是您为其分配的最后一个值。试试这个：

length_b_loop <- length(dat_ftprints)-1

for (b in 1:length_b_loop){
  if (b == 1){
    spc_intersect_poly1 <- dat_ftprints[[b]]
    spc_intersect_poly2 <- dat_ftprints[[b+1]]
    spc_intersect_temp <- raster::intersect(spc_intersect_poly1, spc_intersect_poly2)
  } else {
    spc_intersect_poly3 <- dat_ftprints[[b+1]]
    spc_intersect_temp <- raster::intersect(spc_intersect_temp, spc_intersect_poly3)
  }
}

编辑 首先，我将使用lapply(dat_ftprints,is)检查您的输入数据，以确保它们都是空间多边形数据框。如果它们是这样，则代码应该起作用。下面是从帮助页面构建的多边形示例：

##construct polygons
Sr1 = Polygon(cbind(c(2,4,4,1,2),c(2,2,5,4,2)))
Sr2 = Polygon(cbind(c(5,4,2,5),c(2,5,2,2)))
Sr3 = Polygon(cbind(c(4,2,5,10,4),c(5,3,2,5,5)))

Srs1 = Polygons(list(Sr1), "s1")
Srs2 = Polygons(list(Sr2), "s2")
Srs3 = Polygons(list(Sr3), "s3")

SpP = SpatialPolygons(list(Srs1,Srs2,Srs3), 1:3)
plot(SpP, col = c(rgb(1,0,0,0.25),rgb(0,1,0,0.25),rgb(0,0,1,0.25)), pbg="white")

##construct list of SPDFs
dat_ftprints=list(SpatialPolygonsDataFrame(SpatialPolygons(list(Polygons(list(Sr1), "s1"))), data = data.frame(x=1,row.names = "s1")),
                  SpatialPolygonsDataFrame(SpatialPolygons(list(Polygons(list(Sr2), "s2"))), data = data.frame(x=1,row.names = "s2")),
                  SpatialPolygonsDataFrame(SpatialPolygons(list(Polygons(list(Sr3), "s3"))), data = data.frame(x=1,row.names = "s3")))

##run previous code
length_b_loop <- length(dat_ftprints)-1

for (b in 1:length_b_loop){
  if (b == 1){
    spc_intersect_poly1 <- dat_ftprints[[b]]
    spc_intersect_poly2 <- dat_ftprints[[b+1]]
    spc_intersect_temp <- raster::intersect(spc_intersect_poly1, spc_intersect_poly2)
  } else {
    spc_intersect_poly3 <- dat_ftprints[[b+1]]
    spc_intersect_temp <- raster::intersect(spc_intersect_temp, spc_intersect_poly3)
  }
}

plot(spc_intersect_temp,col="black",add=T)