R Under development (unstable) (2023-09-30 r85239 ucrt) -- "Unsuffered Consequences"
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> options("rgdal_show_exportToProj4_warnings"="none")
> library(sp)
The legacy packages maptools, rgdal, and rgeos, underpinning the sp package,
which was just loaded, were retired in October 2023.
Please refer to R-spatial evolution reports for details, especially
https://r-spatial.org/r/2023/05/15/evolution4.html.
It may be desirable to make the sf package available;
package maintainers should consider adding sf to Suggests:.
> g = SpatialGrid(GridTopology(c(5,5), c(10,10), c(3,3)))
> p = as(g, "SpatialPolygons")
> p$z = c(1,0,1,0,1,0,1,0,1)
> cc = coordinates(g)
> pts = cbind(c(9,21,21,9,9),c(9,9,21,21,9))
> sq = SpatialPolygons(list(Polygons(list(Polygon(pts)), "ID")))
> rnd2 = function(x) round(x, 2)
> 
> 
> proc.time()
   user  system elapsed 
   0.56    0.09    0.65