R Under development (unstable) (2023-07-09 r84667 ucrt) -- "Unsuffered Consequences"
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Platform: x86_64-w64-mingw32/x64

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> #library(rgdal2)
> #openOGRLayer("PG:dbname=postgis" , "meuse2")
> 
> suppressPackageStartupMessages(library(sf))
> options(rgdal_show_exportToProj4_warnings = "none")
> outer = matrix(c(0,0,10,0,10,10,0,10,0,0),ncol=2, byrow=TRUE)
> hole1 = matrix(c(1,1,1,2,2,2,2,1,1,1),ncol=2, byrow=TRUE)
> hole2 = matrix(c(5,5,5,6,6,6,6,5,5,5),ncol=2, byrow=TRUE)
> pol1 = list(outer, hole1, hole2)
> pol2 = list(outer + 12, hole1 + 12)
> pol3 = list(outer + 24)
> mp = list(pol1,pol2,pol3)
> mp1 = st_multipolygon(mp)
> sf = st_sf(a=1, st_sfc(mp1))
> if (suppressPackageStartupMessages(require(sp, quietly = TRUE))) {
+  a = as(sf, "Spatial")
+  print(class(a))
+  b = st_as_sf(a)
+  a2 = as(a, "SpatialPolygonsDataFrame")
+  print(all.equal(a, a2)) # round-trip
+ 
+  b1 = as(a, "sf")
+  print(all.equal(b, b1))
+  b = st_as_sfc(a)
+  b1 = as(a, "sfc")
+  print(all.equal(b, b1))
+ }
[1] "SpatialPolygonsDataFrame"
attr(,"package")
[1] "sp"
[1] TRUE
[1] TRUE
[1] TRUE
> 
> # SpatialMultiPoints
> if (require(sp, quietly = TRUE)) {
+ suppressWarnings(RNGversion("3.5.3"))
+ set.seed(1331)
+ # example(SpatialMultiPoints, ask = FALSE, echo = FALSE) # loads mpdf
+ cl1 = cbind(rnorm(3, 10), rnorm(3, 10))
+ cl2 = cbind(rnorm(5, 10), rnorm(5,  0))
+ cl3 = cbind(rnorm(7,  0), rnorm(7, 10))
+ mpdf = SpatialMultiPointsDataFrame(list(a=cl1, b=cl2, c=cl3), data.frame(a = 1:3, row.names=c("a", "b", "c")))
+ m = st_as_sf(mpdf)
+ all.equal(as(m, "Spatial"), mpdf) # TRUE
+ 
+ demo(meuse, ask = FALSE, echo = FALSE)
+ #meuse = spTransform(meuse, CRS("+proj=longlat +ellps=WGS84 +no_defs"))
+ pol.grd = as(meuse.grid, "SpatialPolygonsDataFrame")
+ #meuse.grd = spTransform(meuse.grid, CRS("+proj=longlat +ellps=WGS84 +no_defs"))
+ #pol.grd = spTransform(pol.grd, CRS("+proj=longlat +ellps=WGS84 +no_defs"))
+ #meuse.area = spTransform(meuse.area, CRS("+proj=longlat +ellps=WGS84 +no_defs"))
+ #meuse.riv = spTransform(meuse.riv, CRS("+proj=longlat +ellps=WGS84 +no_defs"))
+ #summary(st_as_sf(meuse))
+ #summary(st_as_sf(meuse.grd))
+ #x <- st_as_sf(meuse.grid) # don't print: CRS variations.
+ #summary(st_as_sf(meuse.area))
+ #summary(st_as_sf(meuse.riv))
+ #summary(st_as_sf(as(meuse.riv, "SpatialLines")))
+ #summary(st_as_sf(pol.grd))
+ #summary(st_as_sf(as(pol.grd, "SpatialLinesDataFrame")))
+ 
+ nc = st_read(system.file("gpkg/nc.gpkg", package="sf"), "nc.gpkg", quiet = TRUE)
+ all.equal(nc, st_as_sf(as(nc, "Spatial")))
+ st_crs(nc) == st_crs(st_as_sf(as(nc, "Spatial")))
+ 
+ detach("package:sp")
+ }
Warning message:
In CPL_crs_from_input(x) :
  GDAL Message 1: +init=epsg:XXXX syntax is deprecated. It might return a CRS with a non-EPSG compliant axis order.
> 
> proc.time()
   user  system elapsed 
   1.76    0.23    1.98