Downloads a Stamen Maps or Google Maps base layer map using get_map.
download_basemap(
x,
verbose = TRUE,
zoom,
alpha = 1,
source = "stamen",
maptype = "terrain",
...
)Arguments
- x
An object of class
ppi.- verbose
Logical, whether to print information to console.
- zoom
Zoom level (optional), see get_map. An integer from 3 (continent) to 21 (building). By default the zoom level matching the ppi extent is selected automatically.
- alpha
Transparency of the basemap (0-1).
- source
String identifying which map service should be used: "stamen" or "google".
- maptype
Type of basemap to plot. For Stamen Maps: "terrain", "terrain-background", "terrain-labels", "terrain-lines", "toner", "toner-2010", "toner-2011", "toner-background", "toner-hybrid", "toner-labels", "toner-lines", "toner-lite", "watercolor". For Google Maps: "terrain", "satellite", "roadmap", "hybrid"
- ...
Arguments to pass to get_map function.
Details
To use Google Maps as source, you will have to register with Google,
enable billing and provide an API key to ggmap. See the ggmap
README for details.
To use maptype, install the development version of ggmap (>3.0.0) with
devtools::install_github("dkahle/ggmap").
Examples
# load an example scan:
data(example_scan)
# print summary info for the scan:
example_scan
#> Polar scan (class scan)
#>
#> parameters: DBZH VRADH RHOHV ZDR PHIDP
#> elevation angle: 0.5 deg
#> dims: 480 bins x 360 rays
# make ppi for the scan
ppi <- project_as_ppi(example_scan)
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
# \dontrun{
# grab a basemap that matches the extent of the ppi:
basemap <- download_basemap(ppi)
#> Downloading zoom = 9 ...
#> Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.
# map the reflectivity quantity of the ppi onto the basemap:
map(ppi, map = basemap, param = "DBZH")
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
# increase the transparancy of the basemap:
basemap <- download_basemap(ppi, alpha = 0.3)
#> Downloading zoom = 9 ...
#> Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.
map(ppi, map = basemap, param = "DBZH")
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
# download a different type of basemap, e.g. a gray-scale image:
# see get_map() in ggmap library for full documentation of options
basemap <- download_basemap(ppi, maptype = "toner-lite")
#> Downloading zoom = 9 ...
#> Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under ODbL.
# map the radial velocities onto the line image:
map(ppi, map = basemap, param = "VRADH")
#> Warning: CRS object has comment, which is lost in output; in tests, see
#> https://cran.r-project.org/web/packages/sp/vignettes/CRS_warnings.html
# }