将SpatialPointsDataFrame转换为SpatialLinesDataFrame

Question

我正在使用HURDAT数据集绘制飓风轨迹。我目前已经在R中生成了一个SpatialPointsDataFrame对象，它看起来像是2004年的样子。

    > str(cluster.2004.sdf)
Formal class 'SpatialPointsDataFrame' [package "sp"] with 5 slots
  ..@ data       :'data.frame': 2693 obs. of  4 variables:
  .. ..$ Sid      : int [1:2693] 1331 1331 1331 1331 1331 1331 1331 1331 1331 1331 ...
  .. ..$ clusterid: num [1:2693] 2 2 2 2 2 2 2 2 2 2 ...
  .. ..$ name     : Factor w/ 269 levels "","ABBY      ",..: 6 6 6 6 6 6 6 6 6 6 ...
  .. ..$ WmaxS    : num [1:2693] 78.9 82.8 80.9 70.9 76.9 ...
  ..@ coords.nrs : num(0) 
  ..@ coords     : num [1:2693, 1:2] 754377 612852 684956 991386 819565 ...
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : NULL
  .. .. ..$ : chr [1:2] "lon" "lat"
  ..@ bbox       : num [1:2, 1:2] -3195788 1362537 4495870 9082812
  .. ..- attr(*, "dimnames")=List of 2
  .. .. ..$ : chr [1:2] "lon" "lat"
  .. .. ..$ : chr [1:2] "min" "max"
  ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slots
  .. .. ..@ projargs: chr "+proj=lcc +lat_1=60 +lat_2=30 +lon_0=-60 +ellps=WGS84"
    > summary(cluster.2004.sdf)
Object of class SpatialPointsDataFrame
Coordinates:
         min     max
lon -3195788 4495870
lat  1362537 9082812
Is projected: TRUE 
proj4string :
[+proj=lcc +lat_1=60 +lat_2=30 +lon_0=-60 +ellps=WGS84]
Number of points: 2693
Data attributes:
      Sid         clusterid             name         WmaxS       
 Min.   :1331   Min.   :1.000   IVAN      :517   Min.   : 14.83  
 1st Qu.:1334   1st Qu.:2.000   FRANCES   :403   1st Qu.: 31.35  
 Median :1337   Median :3.000   JEANNE    :379   Median : 50.04  
 Mean   :1337   Mean   :2.898   KARL      :283   Mean   : 61.66  
 3rd Qu.:1339   3rd Qu.:4.000   DANIELLE  :271   3rd Qu.: 90.40  
 Max.   :1341   Max.   :4.000   BONNIE    :253   Max.   :142.52  
                                (Other)   :587 

每个风暴都有一个唯一的风暴id参考，标记为"Sid"。我想把SpatialPointsDataFrame按"Sid"分组，并把所有的点转换成一条线。

我尝试了一下plyr包装中的ddply，但坦率地说，我不知道我在做什么。我知道我可以这样做:循环数据帧中的每一行并将坐标附加到列表中，然后使用sp包中的Lines函数转换该列表。

然而，我更喜欢一种更R的转换方式。谢谢理查德。

Answer 1

mdsumner的解决方案的问题是，生成的data.frame每行必须有一行，但在他的代码中，每个点有一行。正确的代码应该是:

## example data
d <- data.frame(x=runif(7), y=runif(7), id = c(rep("a", 3), rep("b", 4)))
library(sp)    
coordinates(d) <- ~x+y
## list of Lines per id, each with one Line in a list
x <- lapply(split(d, d$id), function(x) Lines(list(Line(coordinates(x))), x$id[1L]))
# the corrected part goes here:
lines <- SpatialLines(x)
data <- data.frame(id = unique(d$id))
rownames(data) <- data$id
l <- SpatialLinesDataFrame(lines, data)

所以问题基本上是您必须为行创建一个data.frame，按id分组(每行一行)。在上述情况下，除了id没有数据，这是相当容易的。如果您需要对原始SpatialPointDataFrame的一些其他数据进行分组，则必须使用一些分组功能，如tapply, aggregate，或使用我最喜欢的sqldf:

data <- sqldf('
select id, max(something), sum(something_else)
from d
group by id
')

Answer 2

## example data
d <- data.frame(x=runif(7), y=runif(7), id = c(rep("a", 3), rep("b", 4)))
##split(d, d$id)
library(sp)    
coordinates(d) <- ~x+y
## list of Lines per id, each with one Line in a list
x <- lapply(split(d, d$id), function(x) Lines(list(Line(coordinates(x))), x$id[1L]))
## or one Lines in a list, with all Line objects
## x <- list(Lines(lapply(split(d, d$id), function(x) Line(coordinates(x))), paste(unique(d$id), collapse = "_")))
## etc.
SpatialLines(x, CRS(as.character(NA)))
## need to be careful here, assuming one Lines per original row
## and we trash the original rownames  . . .
SpatialLinesDataFrame(SpatialLines(x, CRS(as.character(NA))), d[,"id", drop = FALSE], match.ID = FALSE)

Answer 3

从空间点DataFrame到空间多边形DataFrame

library(sp)
library(raster)
### Example data: creating a SpatialPointsDataFrame object
x = c(1,2,5,4,3)
y = c(3,2,3,6,6)
df_points <- as.data.frame(cbind(x,y))
S <- SpatialPoints(cbind(x,y))
# S <- SpatialPoints(list(x,y))
# S <- SpatialPoints(data.frame(x,y))
S
plot(S)
spdf <- SpatialPointsDataFrame(S, df_points)
spdf
plot(spdf)
# crs(spdf) <- ("+proj=utm +zone=23 +south +datum=WGS84 +units=m +no_defs") ### add a crs
### Convert the SpatialPointsDataFrame to SpatialPolygons
(Sr1 = Polygon(spdf[,1:2]))
(Srs1 = Polygons(list(Sr1), "s1"))
(SpP = SpatialPolygons(list(Srs1), 1:1, proj4string= crs("+proj=utm +zone=23 +south +datum=WGS84 +units=m +no_defs"))) 
plot(SpP, col = 3:3, pbg="white", add=T) 
SpP ### can not write as shapefile
### Convert the SpatialPolygons to SpatialPolygonsDataFrame
shape_pol <- SpatialPolygonsDataFrame(SpP, match.ID=F, data= data.frame(x=spdf[1:1,1], y=spdf[1:1,2]))
shape_pol ### can be write as shapefile
plot(shape_pol, col = 4, add=T)
### write shapefile
library(rgdal)
writeOGR(shape_pol, paste0(getwd(), "/Output_shapes"), "p_to_shape_pol", driver="ESRI Shapefile")