[R-sig-Geo] how to create several polygons from a list of vertices
Michael Sumner
md@umner @ending from gm@il@com
Wed Aug 15 02:09:57 CEST 2018
Here's another way with spbabel.
library(dplyr)
library(spbabel)
pts <-
tibble::tribble(~ID, ~x, ~y, ~grp,
1 , -33, -23, 1,
2 , -32, -23, 1,
3 , -32, -22, 1,
4 , -33, -22, 1,
5 , -32, -23, 2,
6 , -31, -23, 2,
7 , -31, -22, 2,
8 , -32, -22, 2,
9 , -31, -23, 3,
10, -30, -23, 3,
11, -30, -22, 3,
12, -31, -22, 3,
13, -33, -22, 4,
14, -32, -22, 4,
15, -32, -21, 4,
16, -33, -21, 4,
17, -32, -22, 5,
18, -31, -22, 5,
19, -31, -21, 5,
20, -32, -21, 5,
21, -31, -22, 6,
22, -30, -22, 6,
23, -30, -21, 6,
24, -31, -21, 6)
## objects and branches (parts) are the same level
## objects and branches (parts) are the same level
## and we maintain "grp" as the object attribute data
x <- pts %>% transmute(grp = grp, x_ = x, y_ = y,
object_ = grp, branch_ = grp,
order_ = ID, island_ = TRUE) %>% spbabel::sp()
On Wed, 15 Aug 2018 at 09:25 obrl soil <obrlsoilau using gmail.com> wrote:
> Hi Antonio,
>
> have you tried with sf? Like:
>
> library(sf)
>
> pts <-
> tibble::tribble(~ID, ~x, ~y, ~grp,
> 1 , -33, -23, 1,
> 2 , -32, -23, 1,
> 3 , -32, -22, 1,
> 4 , -33, -22, 1,
> 5 , -32, -23, 2,
> 6 , -31, -23, 2,
> 7 , -31, -22, 2,
> 8 , -32, -22, 2,
> 9 , -31, -23, 3,
> 10, -30, -23, 3,
> 11, -30, -22, 3,
> 12, -31, -22, 3,
> 13, -33, -22, 4,
> 14, -32, -22, 4,
> 15, -32, -21, 4,
> 16, -33, -21, 4,
> 17, -32, -22, 5,
> 18, -31, -22, 5,
> 19, -31, -21, 5,
> 20, -32, -21, 5,
> 21, -31, -22, 6,
> 22, -30, -22, 6,
> 23, -30, -21, 6,
> 24, -31, -21, 6)
>
> squares <- split(pts, pts$grp)
> squares <- lapply(squares, function(g) {
> # get just coords
> g <- as.matrix(g[, c(2,3)])
> # repeat first point last to close poly
> g <- rbind(g, g[1, ])
> # convert to an sf polygon object
> gp <- sf::st_polygon(list(g))
> # make sure the vertices are in an order
> # that complies with the simple
> # features standard
> gp <- sf::st_buffer(gp, 0L)
> })
> # turn list of polygons into geometry column
> squares_sfc <- sf::st_sfc(squares) # can add crs = ?? to this call
> # add an ID to make an sf data frame
> squares_sf <- sf::st_sf('ID' = seq(6), 'geometry' = squares_sfc)
>
> # if you still need to use sp for whatever reason
> squares_sp <- as(squares_sf, "Spatial")
>
> Regards,
> @obrl_soil
>
> On Wed, Aug 15, 2018 at 8:03 AM, Antonio Silva <aolinto.lst using gmail.com>
> wrote:
> > Thanks Lulla,
> >
> > Nice solution. I could also export it as a shapefile after transforming
> it
> > to a spatial polygon dataframe.
> >
> > The problem is that I could not "individualize" the squares in a
> multipart
> > layer. They all have the same ID. I tried to change this without success:
> > "Single ID required".
> >
> > The attribute table of the shapefile should have 6 lines in my example
> and
> > not only one.
> >
> > Any other option?
> >
> > Thanks again,
> >
> > Antonio Olinto
> >
> >
> > Em ter, 14 de ago de 2018 às 18:10, Vijay Lulla <vijaylulla using gmail.com>
> > escreveu:
> >
> >> Maybe something like this?
> >>
> >> poly <- SpatialPolygons(list(Polygons(tapply(seq_len(nrow(vertices)),
> >> vertices$cod,
> >> function(x)
> >> Polygon(vertices[x,1:2])), ID="1")),
> >> proj4string=CRS("+proj=longlat +ellps=WGS84
> >> +datum=WGS84 +no_defs"))
> >>
> >>
> >> On Tue, Aug 14, 2018 at 4:17 PM Antonio Silva <aolinto.lst using gmail.com>
> >> wrote:
> >>
> >>> Hi,
> >>>
> >>> I have a data.frame with the vertices (lon / lat) and codes from
> several
> >>> squares (more than 500 in the real dataset).
> >>> I want to create an object with these polygons (squares) and after this
> >>> export it as a shapefile.
> >>> With the script below I can draw one square.
> >>> library(sp)
> >>> P1 = Polygon(vertices[1:4,1:2])
> >>> Ps1 = SpatialPolygons(list(Polygons(list(P1), ID = "1")),
> >>> proj4string=CRS("+proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs"))
> >>> plot(Ps1, axes = TRUE)
> >>>
> >>> Now I'm trying to create one object with all squares at once.
> >>> Is it possible?
> >>>
> >>> Thanks a lot,
> >>>
> >>> Antônio Olinto
> >>>
> >>> sample data:vertices
> >>> lon lat cod
> >>> 1 -33 -23 1
> >>> 2 -32 -23 1
> >>> 3 -32 -22 1
> >>> 4 -33 -22 1
> >>> 5 -32 -23 2
> >>> 6 -31 -23 2
> >>> 7 -31 -22 2
> >>> 8 -32 -22 2
> >>> 9 -31 -23 3
> >>> 10 -30 -23 3
> >>> 11 -30 -22 3
> >>> 12 -31 -22 3
> >>> 13 -33 -22 4
> >>> 14 -32 -22 4
> >>> 15 -32 -21 4
> >>> 16 -33 -21 4
> >>> 17 -32 -22 5
> >>> 18 -31 -22 5
> >>> 19 -31 -21 5
> >>> 20 -32 -21 5
> >>> 21 -31 -22 6
> >>> 22 -30 -22 6
> >>> 23 -30 -21 6
> >>> 24 -31 -21 6
> >>>
> >>> [[alternative HTML version deleted]]
> >>>
> >>> _______________________________________________
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> >>> https://stat.ethz.ch/mailman/listinfo/r-sig-geo
> >>>
> >>
> >
> > [[alternative HTML version deleted]]
> >
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>
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--
Dr. Michael Sumner
Software and Database Engineer
Australian Antarctic Division
203 Channel Highway
Kingston Tasmania 7050 Australia
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