set_projection: Set and get the map projection

Description

The function set_projection sets the projection of a shape file. It is a convenient wrapper of spTransform and projectRaster with shortcuts for commonly used projections. The projection can also be set directly in the plot call with tm_shape. This function is also used to set the current projection information if this is missing. The function get_projection is used to get the projection information.

Usage

set_projection(shp, projection = NA, current.projection = NA,
  overwrite.current.projection = FALSE)
get_projection(shp, as.CRS = FALSE, guess.longlat = FALSE)

Arguments

shp

shape object of class Spatial, Raster, or sf (see details).

projection

new projection. See get_proj4 for options. This argument is only used to transform the shp. Use current.projection to specify the current projection of shp.

current.projection

the current projection of shp. See get_proj4 for possible options. Only use this if the current projection is missing or wrong.

overwrite.current.projection

logical that determines whether the current projection is overwritten if it already has a projection that is different.

as.CRS

should a CRS object be returned instead of a PROJ.4 character string? Default is FALSE.

guess.longlat

if TRUE, it checks if the coordinates are within -180/180 and -90/90, and if so, it returns the WGS84 longlat projection (which is get_proj4("longlat")).

Value

set_projection returns a (transformed) shape object with updated projection information. get_projection returns the PROJ.4 character string of shp.

Details

For raster objects, the projection method is based on the type of data. For numeric layers, the bilinear method is used, and for categorical layers the nearest neighbor. See projectRaster for details.

References

Tennekes, M., 2018, tmap: Thematic Maps in R, Journal of Statistical Software, 84(6), 1-39, DOI