happign (version 0.3.3)

get_wms_raster: Download WMS raster layer

Description

Download a raster layer from the IGN Web Mapping Services (WMS). Specify a location using a shape and provide the layer name.

Usage

get_wms_raster(x,
               layer = "ORTHOIMAGERY.ORTHOPHOTOS",
               res = 10,
               crs = 2154,
               rgb = TRUE,
               filename = NULL,
               overwrite = FALSE,
               verbose = TRUE,
               interactive = FALSE)

Value

SpatRaster object from terra package.

Arguments

x

Object of class sf or sfc, located in France.

layer

character; layer name obtained from get_layers_metadata("wms-r") or the IGN website.

res

numeric; resolution specified in the units of the coordinate system (e.g., meters for EPSG:2154, degrees for EPSG:4326). See details for more information.

crs

numeric, character, or object of class sf or sfc; defaults to EPSG:2154. See sf::st_crs() for more details.

rgb

boolean; if set to TRUE, downloads an RGB image. If set to FALSE, downloads a single band with floating point values. See details for more information.

filename

character or NULL; specifies the filename or an open connection for writing (e.g., "test.tif" or "~/test.tif"). The default format is ".tif" but all GDAL drivers are supported. When a filename is provided, the function uses it as a cache: if the file already exists and overwrite is set to FALSE, the function will directly load the raster from that file instead of re-downloading it.

overwrite

boolean; if TRUE, the existing raster will be overwritten.

verbose

boolean; if TRUE, message are added.

interactive

logical; if TRUE, an interactive menu prompts for apikey and layer argument.

Details

• res: Note that setting res higher than the default resolution of the layer will increase the number of pixels but not the precision of the image. For instance, downloading the BD Alti layer from IGN is optimal at a resolution of 25m.

• rgb: Rasters are commonly used to download images such as orthophotos. In specific cases like DEMs, however, a value per pixel is essential. See examples below.

See Also

get_layers_metadata()

Examples

if (FALSE) {
library(sf)
library(tmap)

# Shape from the best town in France
penmarch <- read_sf(system.file("extdata/penmarch.shp", package = "happign"))

# For quick testing use interactive = TRUE
raster <- get_wms_raster(x = penmarch, res = 25, interactive = TRUE)

# For specific data, choose apikey with get_apikey() and layer with get_layers_metadata()
apikey <- get_apikeys()[4]  # altimetrie
metadata_table <- get_layers_metadata("wms-r", apikey) # all layers for altimetrie wms
layer <- metadata_table[2,1] # ELEVATION.ELEVATIONGRIDCOVERAGE

# Downloading digital elevation model values not image
mnt_2154 <- get_wms_raster(penmarch, layer, res = 1, crs = 2154, rgb = FALSE)

# If crs is set to 4326, res is in degrees
mnt_4326 <- get_wms_raster(penmarch, layer, res = 0.0001, crs = 4326, rgb = FALSE)

# Plotting result
tm_shape(mnt_4326)+
   tm_raster()+
tm_shape(penmarch)+
   tm_borders(col = "blue", lwd  = 3)
}