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, limit = NULL, ..., source = NULL)a four element vector of extent c(xmin, xmax, ymin, ymax)
target specification (PROJ.4 string or epsg code)
if used, a one or two element numeric vector to give the maximum radius to the edge of the extent from the middle
arguments passed to proj4::ptransform()
source specification (PROJ.4 string or epsg code)
four value extent c(xmin, xmax, ymin, ymax)
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 1111783 0 2209293