getelev {IsoriX}

Download an elevation raster from internet

Description

The function getelev downloads an elevation raster from internet. It is a wrapper that 1) calls the function elevatr::get_elev_raster to download the data and 2) saves the downloaded raster on the hard drive (so that you don't have to keep downloading the same file over and over again). The file saved on the disk is a *.tif file which you can directly read using the function terra::rast.

Usage

getelev(
  file = "~/elevation_world_z5.tif",
  z = 5,
  long_min = -180,
  long_max = 180,
  lat_min = -90,
  lat_max = 90,
  margin_pct = 5,
  override_size_check = FALSE,
  overwrite = FALSE,
  Ncpu = getOption_IsoriX("Ncpu"),
  verbose = interactive(),
  ...
)

Arguments

file

A string indicating where to store the file on the hard drive (default = ⁠~/elevation_world_z5.tif⁠)

z

An integer between 1 and 14 indicating the resolution of the file do be downloaded (1 = lowest, 14 = highest; default = 5)

long_min

A numeric indicating the minimum longitude to select from. Should be a number between -180 and 180 (default = -180).

long_max

A numeric indicating the maximal longitude to select from. Should be a number between -180 and 180 (default = 180).

lat_min

A numeric indicating the minimum latitude to select from. Should be a number between -90 and 90 (default = -90).

lat_max

A numeric indicating the maximal latitude to select from (default = 90).

margin_pct

The percentage representing by how much the area should extend outside the area used for cropping (default = 5, corresponding to 5%). Set to 0 if you want exact cropping.

override_size_check

A logical indicating whether or not to override size checks (default = FALSE)

overwrite

A logical indicating if an existing file should be re-downloaded

Ncpu

An integer specifying the number of CPU's to use when downloading AWS tiles (default set by global package options).

verbose

A logical indicating whether information about the progress of the procedure should be displayed or not while the function is running. By default verbose is TRUE if users use an interactive R session and FALSE otherwise.

...

Other parameters to be passed to the function elevatr::get_elev_raster

Details

By default (and to keep with the spirit of the former implementations of getelev in IsoriX, which did not rely on elevatr::elevatr), an elevation raster of the whole world is downloaded with a resolution correspond to ca. 0.6 km2 per raster cell. You can increase the resolution by increasing the value of the argument z. You can also restrict the area to be downloaded using the arguments long_min, long_max, lat_min & lat_max.

Note that when using prepraster you will be able to reduce the resolution and restrict the boundaries of this elevation raster, but you won't be able to increase the resolution or expend the boundaries. As a consequence, it is probably a good idea to overshoot a little when using getelev and download data at a resolution slightly higher than you need and for a extent larger than your data.

You can customise further what you download by using other parameters of elevatr::get_elev_raster (via the elipsis ...).

Please refer to the documentation of elevatr::get_elev_raster for information on the sources and follows link in there to know how to cite them.

Value

This function returns the full path where the file has been stored

Examples

## To download the high resolution
## raster at the default location, just type:
## getelev()