[R-sig-Geo] How to delete some polygons from 'SpatialPolygonsDataFrame'
Roger Bivand
Roger.Bivand at nhh.no
Fri Nov 28 11:38:10 CET 2014
On Fri, 28 Nov 2014, Frede Aakmann Tøgersen wrote:
> Hi
>
> If nsw_lga[153, ] is the island that you do not want to plot then you can do
I think that the problem is that only Polygon objects 1:12 in Polygons
object 153 are the islands, while 13:14 are larger and do not have
label point longitude > 159. One possibility then is to take out the
Polygons object (using Scotland in rgdal as an example and recalling
Barry Rowlingson's insight that someone added slivers of islands to their
desired proximate neighbours - so part of 48 Shetland is on Orkney):
library(rgdal)
dsn <- system.file("vectors", package = "rgdal")[1]
scot_BNG <- readOGR(dsn=dsn, layer="scot_BNG")
plot(scot_BNG)
plot(scot_BNG[48,], col="red", add=TRUE)
library(spdep)
nb <- poly2nb(scot_BNG)
plot(nb, coordinates(scot_BNG), add=TRUE)
If we drop Shetland and Fair Isle (using a latitude cutoff):
scot_BNG1 <- scot_BNG
pols48 <- slot(scot_BNG1, "polygons")[[48]]
pol48 <- slot(pols48, "Polygons")
length(pol48)
sapply(pol48, function(x) {slot(x, "labpt")[2]})
res <- pol48[sapply(pol48, function(x) {slot(x, "labpt")[2]}) < 1050000]
slot(pols48, "Polygons") <- res
slot(scot_BNG1, "polygons")[[48]] <- pols48
plot(scot_BNG1, lwd=3, add=TRUE)
bbox(scot_BNG)
bbox(scot_BNG1)
we appear to get what we want (but the plot order and bounding box of the
SpatialPolygons object are not updated to match the exclusion).
Alternatively, and reconstructing the object, use rgeos:
library(rgeos)
bb <- bbox(scot_BNG)
plot(scot_BNG)
plot(scot_BNG[48,], col="red", add=TRUE)
crds <- cbind(x=c(bb[1, 1]-1, bb[1, 1]-1, bb[1, 2]+1, bb[1, 2]+1,
bb[1, 1]-1), y=c(bb[2, 1]-1, 1050000, 1050000, bb[2, 1]-1, bb[2, 1]-1))
c1 <- SpatialPolygons(list(Polygons(list(Polygon(crds)), "1")),
proj4string=CRS(proj4string(scot_BNG)))
plot(c1, add=TRUE, lty=2)
scot_BNG2a <- gIntersection(scot_BNG, c1, byid=c(TRUE, FALSE))
scot_BNG2b <- SpatialPolygonsDataFrame(scot_BNG2a, data=slot(scot_BNG,
"data"))
plot(scot_BNG2b, lwd=3, add=TRUE)
bbox(scot_BNG)
bbox(scot_BNG2b)
Hope this clarifies,
Roger
>
> plot(nsw_lga[ -153, ])
>
> or you can set an xlim in plot()
>
> plot(nsw_lga, xlim = c(140, 153))
>
> you may perhaps need play with the settings of xlim to find the right ones.
>
> If you want to have an object without the island then do
>
> nsw_lga_wo_island <- nsw_lga[ -153, ]
>
> Something like
>
> nsw_lga[ -153, ] <- NULL doesn't seem to work. Don't know if something similar will work.
>
>
> Yours sincerely / Med venlig hilsen
>
>
> Frede Aakmann Tøgersen
> Specialist, M.Sc., Ph.D.
> Plant Performance & Modeling
>
> Technology & Service Solutions
> T +45 9730 5135
> M +45 2547 6050
> frtog at vestas.com
> http://www.vestas.com
>
> Company reg. name: Vestas Wind Systems A/S
> This e-mail is subject to our e-mail disclaimer statement.
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> If you have received this e-mail in error please contact the sender.
>
>> -----Original Message-----
>> From: R-sig-Geo [mailto:r-sig-geo-bounces at r-project.org] On Behalf Of
>> Jianyun Wu
>> Sent: 28. november 2014 06:33
>> To: R-sig-Geo at r-project.org
>> Subject: [R-sig-Geo] How to delete some polygons from
>> 'SpatialPolygonsDataFrame'
>>
>> Dear list,
>>
>> I usually use 'readOGR()' from rgdal package in R to input the ESRI
>> shapefile.
>> So the inputted data are SpatialPolygonsDataFrame.
>>
>> I am processing the New South Wales, Australia map for a spatial analysis.
>> There is an island far away from the mainland, which I want to delete it
>> from the map when I plot NSW. Because it makes the whole plot small due
>> to
>> its long distant.
>>
>> Below is the area contains the polygons of this island and surrounding
>> islands. There are 14 "@Polygons" contributing to the entire area. From
>> some experiments, I know that it is Polygon 3-14 making the distant
>> islands.
>>
>> Is there a simple way that I can delete those small polygons from this area
>> polygon and their attributes from the data
>>
>> Thank you
>>
>> Fred
>>
>> str(nsw_lga[153, ])
>> Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
>> ..@ data :'data.frame': 1 obs. of 3 variables:
>> .. ..$ STATE_CODE: Factor w/ 9 levels "1","2","3","4",..: 1
>> .. ..$ LGA_CODE11: Factor w/ 565 levels "10050","10110",..: 153
>> .. ..$ LGA_NAME11: Factor w/ 564 levels "Adelaide (C)",..: 483
>> ..@ polygons :List of 1
>> .. ..$ :Formal class 'Polygons' [package "sp"] with 5 slots
>> .. .. .. ..@ Polygons :List of 14
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 3.83e-07
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:38, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 4.69e-07
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:13, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 7.82e-07
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:31, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 1.02e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:47, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 1.14e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:22, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.6
>> .. .. .. .. .. .. ..@ area : num 1.38e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:24, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 1.52e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:26, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 2.05e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:32, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 2.61e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:36, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 4.27e-06
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:109, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.5
>> .. .. .. .. .. .. ..@ area : num 1.42e-05
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:85, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 159.1 -31.6
>> .. .. .. .. .. .. ..@ area : num 0.00152
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:2929, 1:2] 159 159 159 159 159 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 142.2 -30.7
>> .. .. .. .. .. .. ..@ area : num 8.79
>> .. .. .. .. .. .. ..@ hole : logi FALSE
>> .. .. .. .. .. .. ..@ ringDir: int 1
>> .. .. .. .. .. .. ..@ coords : num [1:5178, 1:2] 144 144 144 144 144 ...
>> .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
>> .. .. .. .. .. .. ..@ labpt : num [1:2] 141.5 -31.9
>> .. .. .. .. .. .. ..@ area : num 0.0162
>> .. .. .. .. .. .. ..@ hole : logi TRUE
>> .. .. .. .. .. .. ..@ ringDir: int -1
>> .. .. .. .. .. .. ..@ coords : num [1:131, 1:2] 141 141 141 141 141 ...
>> .. .. .. ..@ plotOrder: int [1:14] 13 14 12 11 10 9 8 7 6 5 ...
>> .. .. .. ..@ labpt : num [1:2] 142.2 -30.7
>> .. .. .. ..@ ID : chr "152"
>> .. .. .. ..@ area : num 8.79
>> ..@ plotOrder : int 1
>> ..@ bbox : num [1:2, 1:2] 141 -33.4 159.1 -29
>> .. ..- attr(*, "dimnames")=List of 2
>> .. .. ..$ : chr [1:2] "x" "y"
>> .. .. ..$ : chr [1:2] "min" "max"
>> ..@ proj4string:Formal class 'CRS' [package "sp"] with 1 slot
>> .. .. ..@ projargs: chr "+proj=longlat +ellps=GRS80 +no_defs"
>>
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--
Roger Bivand
Department of Economics, Norwegian School of Economics,
Helleveien 30, N-5045 Bergen, Norway.
voice: +47 55 95 93 55; fax +47 55 95 91 00
e-mail: Roger.Bivand at nhh.no
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