A four figure extent (xmin, xmax, ymin, ymax) is used to approximate the boundary of its reprojected version by interpolating new vertices along each edge.
reproj_extent(extent, target, ..., source = NULL, dimension = c(64, 64))a four element vector of extent c(xmin, xmax, ymin, ymax), or matrix with 4 columns
target specification (PROJ.4 string or epsg code)
arguments passed to proj4::ptransform()
source specification (PROJ.4 string or epsg code)
a 2 element integer to give the discretization within each extent (defaults to 64x64)
four value extent c(xmin, xmax, ymin, ymax) or a matrix with four columns (matching the input)
This is a simple version of what GDAL's 'SuggestedWarpOutput' does, and similar functions like the raster package 'projectExtent()'.
Internal functions unpack the various stages, and might be exposed in future. These stages are
interpolate around the boundary with correct ordering (can be used as a polygon or line)
reproject the interpolated boundary
summarize the interpolated boundary to the new extent
reproj_extent(c(0, 10, 0, 20), "+proj=laea", source = "+proj=longlat")
#> [1] 0 1129109 0 2243734