Decimal degree grid from polar stereographic spatial objects

Outputs a list of grid lines that can be used to plot a grid on polar stereographic maps. Requires a spatial object projected using UTM coordinates

deg_grid_polar(
  dat,
  lat.interval = 10,
  lon.interval = 45,
  n.points = 1000,
  proj4.utm = TRUE,
  proj4.deg = "+proj=longlat +datum=WGS84"
)

Arguments

dat	Spatial object projected using UTM coordinates, such as `readShapeSpatial` OR a numeric vector of length 4 where first element defines the minimum longitude, second element the maximum longitude, third element the minimum latitude and fourth element the maximum latitude of the bounding box.
lat.interval	the interval of latitude grids for polar stereographic maps (`type = "arctic50"` or `"arctic60"`)
lon.interval	the interval of longitude grids for polar stereographic maps (`type = "arctic50"` or `"arctic60"`)
n.points	number of points used in creating the grid lines. The more points, the smoother the lines.
proj4.utm	projection in `dat`. If TRUE (default), fetches the projection from `dat`. If `dat` is a numeric vector and `proj4.utm = TRUE`, `CRS("+init=epsg:32633")` is used as UTM projection (the same projection than in Svalbard shapefiles).
proj4.deg	desired decimal degree projection. Uses a reasonable default projection. Do not change.
round.map	logical indicating whether the desired map is round `TRUE` or square `FALSE`. Bypasses certain routines, which caused errors.

Returns a UTM coodrinate grid.