r - 从嵌套的 SpatialPolygonsDataFrame 中提取父多边形或从父多边形中提取 'Dissolving' 孔

Question

编辑 经过更多研究但仍然没有解决方案，我添加了实质性编辑以及指向 .shp 文件的链接。

The shape file is included here

我有一个包含 9 个多边形的 SpatialPolygonsDataFrame，每个多边形还包含多个嵌套多边形 - “孔”。数据摘要在这里。

> summary(data)
Object of class SpatialPolygonsDataFrame
Coordinates:
        min       max
x  483298.9  643204.4
y 4782172.1 4997248.3
Is projected: TRUE 
proj4string :
[+proj=utm +zone=12 +datum=WGS84 +units=m +no_defs +ellps=WGS84 +towgs84=0,0,0]
Data attributes:
       Id          IndID  
 Min.   :0   BHS_011_A:1  
 1st Qu.:0   BHS_015_A:1  
 Median :0   BHS_083_A:1  
 Mean   :0   BHS_089_A:1  
 3rd Qu.:0   BHS_091_A:1  
 Max.   :0   BHS_129_A:1  
             (Other)  :3  

数据的结构示例如下。

Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
  ..@ data       :'data.frame': 9 obs. of  2 variables:
  .. ..$ Id   : int [1:9] 0 0 0 0 0 0 0 0 0
  .. ..$ IndID: Factor w/ 9 levels "BHS_011_A","BHS_015_A",..: 1 2 3 4 5 6 7 8 9
  ..@ polygons   :List of 9
  .. ..$ :Formal class 'Polygons' [package "sp"] with 5 slots
  .. .. .. ..@ Polygons :List of 5
  .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
  .. .. .. .. .. .. ..@ labpt  : num [1:2] 513497 4986246
  .. .. .. .. .. .. ..@ area   : num 76614017
  .. .. .. .. .. .. ..@ hole   : logi FALSE
  .. .. .. .. .. .. ..@ ringDir: int 1
  .. .. .. .. .. .. ..@ coords : num [1:287, 1:2] 509244 507384 507214 507010 506899 ...
  .. .. .. .. .. .. .. ..- attr(*, "dimnames")=List of 2
  .. .. .. .. .. .. .. .. ..$ : NULL
  .. .. .. .. .. .. .. .. ..$ : chr [1:2] "x" "y"
  .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
  .. .. .. .. .. .. ..@ labpt  : num [1:2] 509678 4979511
  .. .. .. .. .. .. ..@ area   : num 1462398
  .. .. .. .. .. .. ..@ hole   : logi TRUE
  .. .. .. .. .. .. ..@ ringDir: int -1
  .. .. .. .. .. .. ..@ coords : num [1:7, 1:2] 509301 509269 509194 509007 509412 ...
  .. .. .. .. .. .. .. ..- attr(*, "dimnames")=List of 2
  .. .. .. .. .. .. .. .. ..$ : NULL
  .. .. .. .. .. .. .. .. ..$ : chr [1:2] "x" "y"
  .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
  .. .. .. .. .. .. ..@ labpt  : num [1:2] 515572 4988493
  .. .. .. .. .. .. ..@ area   : num 1579348
  .. .. .. .. .. .. ..@ hole   : logi TRUE
  .. .. .. .. .. .. ..@ ringDir: int -1
  .. .. .. .. .. .. ..@ coords : num [1:10, 1:2] 514520 514570 514684 516501 515996 ...
  .. .. .. .. .. .. .. ..- attr(*, "dimnames")=List of 2
  .. .. .. .. .. .. .. .. ..$ : NULL
  .. .. .. .. .. .. .. .. ..$ : chr [1:2] "x" "y"

如下例(九个之一)所示，父多边形有多个孔。

data <- readOGR(".", "IndLineBuff")
plot(data[data$IndID == "MTG_005_A",])

这是我第一次涉足 sp()、rgdal()、rgeos() 和其他空间包，我有找到了许多关于使用运算符提取区域等有用的帖子，但问题仍然存在。同时this post提供接近的解决方案，我似乎无法调整代码以满足此处描述的需求。

我想获得一个 SpatialPolygonsDataFrame，它只包含来自每组子列表(即 data@polygon)的父(最大)多边形。看来我应该能够只提取父多边形或“溶解”孔。

最终的结果是 9 个多边形，每个都是 9 个列表的父项，我可以将其导出为 ESRI shapefile。

如有任何建议，我们将不胜感激。

Answer 1

当我第一次学习 sp 和相关包时，我发现 Barry Rowlingson 的网站非常有用。

它包括:

• 备忘单
  非常有用的引用表，其中包含有关如何做事的提示使用 R 包\ http://www.maths.lancs.ac.uk/~rowlings/Teaching/UseR2012/cheatsheet.html

• 空间简介
  spatialDataframe 结构的解释包 sp。还解释了 CRS(坐标引用系统)和投影(proj4string 和 proj4.Project)。最后还有涵盖光栅图像的使用和操作，以及提取来自他们的数据使用 R\ http://www.maths.lancs.ac.uk/~rowlings/Teaching/UseR2012/static/talk1.pdf

谈到你的问题，这很困惑，因为你正在处理一连串的事情，但这是可以做到的。

下面的代码似乎可以工作(我已经在我已有的 shapefile 上测试了它(一点)，而不是下载你的)。如果您在读入后将 NSWACTA 替换为您的 shapefile 的名称，它应该适合您的情况。虽然没有 promise :-)。

第一部分是介绍性的，展示所有类列表的情况。希望这可以帮助您弄清楚发生了什么。它是 dropHole 函数，它是实际执行您想要的操作的方法。

class(NSWACTA)
# NSWACTA has class sp::SpatialPolygonsDataFrame
slotNames(NSWACTA)
# The SpatialPolygonsDataFrame has a slot called @polygons
class(NSWACTA@polygons)
# The @polgyons slot contains a list
class(NSWACTA@polygons[[1]])
# Elements of that list are of class sp::Polygons 
slotNames(NSWACTA@polygons[[1]])
# An sp::Polygons class has several slots, one of which is @Polygons
class(NSWACTA@polygons[[1]]@Polygons)
# The @Polygons slot contains a list
class(NSWACTA@polygons[[1]]@Polygons[[1]])
# The entries in the @Polygons list are of class sp::Polygon
slotNames(NSWACTA@polygons[[1]]@Polygons[[1]])
# An sp::Polygon has several slots. 
# @coords holds the coordinates which define the boundary.
# @hole is a logical field indicating whether or not the sp::Polygon is a hole 

setGeneric('dropHole',def=function(poly, ...){
  standardGeneric('dropHole')
})

# Drop a single sp::Polygon if it is holey
setMethod('dropHole',signature=signature('Polygon'),
          def=function(poly) {
            #return only Polygons which are not holes
            if (poly@hole) NULL else poly
          }
          )

# Drop holey sp::Polygon entries in the @Polygons list of an sp::Polygons class
setMethod('dropHole', signature = signature('Polygons'),
          def = function(poly) {
            noHoles <- lapply(poly@Polygons, dropHole)
            #Remove the NULL entries from the list
            noHoles <- Filter(Negate(is.null), noHoles)
            # Turn back into a (single) Polygons
            # The generator function (sp::Polygons) fills in the other slots!
            # return the new sp:Polygons object
            sp::Polygons(noHoles, ID = poly@ID)
          }
          )

# Drop holey parts of sp::Polygons in the @polygons list 
# of an sp::SpatialPolygonsDataFrame
setMethod('dropHole', signature = signature('SpatialPolygonsDataFrame'),
          def = function(poly) {
            noHoles <- lapply(poly@polygons, dropHole)
            # Put the un holey Polygons list back into the @polygons slot 
            poly@polygons <- noHoles
            #return the modified SpatialPolygonsDataFrame 
            poly
          }
          )

newmap <- dropHole(NSWACTA)

这是第一部分的输出。 注意 注意名字大小写、单数和复数的区别! (即多边形、多边形和多边形)

d> class(NSWACTA)
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"
d> # NSWACTA has class sp::SpatialPolygonsDataFrame
d> slotNames(NSWACTA)
[1] "data"        "polygons"    "plotOrder"   "bbox"        "proj4string"
d> # The SpatialPolygonsDataFrame has a slot called @polygons
d> class(NSWACTA@polygons)
[1] "list"
d> # The @polgyons slot contains a list
d> class(NSWACTA@polygons[[1]])
[1] "Polygons"
attr(,"package")
[1] "sp"
d> # Elements of that list are of class sp::Polygons 
d> slotNames(NSWACTA@polygons[[1]])
[1] "Polygons"  "plotOrder" "labpt"     "ID"        "area"     
d> # An sp::Polygons class has several slots, one of which is @Polygons
d> class(NSWACTA@polygons[[1]]@Polygons)
[1] "list"
d> # The @Polygons slot contains a list
d> class(NSWACTA@polygons[[1]]@Polygons[[1]])
[1] "Polygon"
attr(,"package")
[1] "sp"
d> # The entries in the @Polygons list are of class sp::Polygon
d> slotNames(NSWACTA@polygons[[1]]@Polygons[[1]])
[1] "labpt"   "area"    "hole"    "ringDir" "coords" 
d> # An sp::Polygon has several slots. 
d> # @coords holds the coordinates which define the boundary.
d> # @hole is a logical field indicating whether or not the sp::Polygon is a hole