add_gps_to_rayshader    Adds a GPS trace to a 'rayshader' scene
crop_raster_square      Crops a raster and returns a smaller square
                        raster
crop_raster_track       Crops a raster into a rectangle surrounding a
                        set of lat long points
dplyr_data              .data to allow column name use in dplyr
drybrush                Simulates a dry brushing effect. Differs from
                        elevation_transparency() in that colour is
                        applied based on local altitude peaks, not
                        across the whole raster
elevation_shade         Produces an elevation shaded image from a
                        raster
elevation_transparency
                        Turns overlay images transparent based on
                        altitude. Can be used to create an image
                        overlay that will only apply to valleys, or
                        only to hills.
example_igc             Returns an example IGC file using read_igc()
example_raster          Returns an example digital elevation model
                        raster file()
get_slippy_map          Obtains and merges map tiles from various
                        sources using the 'slippymath' package
ggslippy                Adds a layer created using slippy_overlay() or
                        slippy_raster() to a 'ggplot2' chart
latlong_to_rayshader_coords
                        Converts WGS84 lat long points into 'rayshader'
                        coordinates. Useful for adding arbitrary points
                        and text to a 'rayshader' scene.
mapbox_dem              Gets Digital Elevation Model (DEM) data from
                        'mapbox'
mapzen_dem              Gets Digital Elevation Model (DEM) data from
                        'mapzen' via 'Amazon Public Datasets'
mosaic_files            Stitches together files into a single raster
                        Requires a target directory of files that can
                        be read with raster::raster(), e.g. .asc files,
                        or a directory of .zip files containing these
                        files
raster_zscale           Approximates the zscale of a raster Digital
                        Elevation Model for 'rayshader'
read_igc                Load an IGC file
slippy_overlay          Creates an overlay image from 'Mapbox' or
                        'Stamen' Maps using the 'slippymath' package
slippy_raster           Creates a square raster centred on any lat long
                        point, or a rectangular raster surrounding a
                        set of lat long points from 'Mapbox', 'Mapzen'
                        or 'Stamen' Maps using the 'slippymath' package
