dc.coastline: Download and Cache a Coastline File

In dankelley/dc: Download and Cache Data

Description

Constructs a query to the NaturalEarth server (ref 1) to download coastline data (or lake data, river data, etc) in any of three resolutions, and caches the resultant file.

Usage

dc.coastline(
  resolution,
  item = "coastline",
  server = "naturalearth",
  destdir = ".",
  destfile,
  force = FALSE,
  dryrun = FALSE,
  debug = getOption("oceDebug")
)

Arguments

resolution	A character value specifying the desired resolution. The permitted choices are "10m" (for 1:10M resolution, the most detailed), "50m" (for 1:50M resolution) and "110m" (for 1:110M resolution). If resolution is not supplied, "50m" will be used.
item	A character value indicating the quantity to be downloaded. This is normally one of "coastline", "land", "ocean", "rivers_lakes_centerlines", or "lakes", but the NaturalEarth server has other types, and advanced users can discover their names by inspecting the URLs of links on the NaturalEarth site, and use them for item. If item is not supplied, it defaults to "coastline".
server	character value giving the base name of the server, used in the construction of URL queries. Since servers tend to change over time, this is a good argument to check, when debugging code that once worked but now fails.
destdir	character value indicating the directory in which to store downloaded files. The default value of "." means to store the downloaded file in the present working directory. Set destdir=NULL if destfile is a filename with full path information. File clutter is reduced by creating a top-level directory called data, with subdirectories for various file types; see “Examples”.
destfile	character value indicating the name of the file. If not supplied, then the file name is constructed from the other parameters of the function call, so that subsequent calls with the same parameters will yield the same result; this is useful for caching.
force	A logical value that indicates whether to force the download, even if the pathname constructed from destdir and destfile already exists.
dryrun	A logical value that indicates whether to return the constructed web query, without attempting to download the file. This can be helpful in designing responses to changing URLs.
debug	an integer specifying whether debugging information is to be printed during processing. The printing is done by a call to dcDebug(). Setting debug=0 turns off this form of debugging, while higher values yield more information. If one dc function calls another, it passes the value of debug but decreased by 1, which means that the value of debug controls not just the breadth of debugging, but also the depth.

Value

A character value indicating the filename of the result; if there is a problem of any kind, the result will be the empty string.

References

1. The NaturalEarth server is at http://www.naturalearthdata.com

See Also

The work is done with utils::download.file().

The work is done with dc().

Other functions that download ocean-related data: dc.g1sst(), dc.hydrography(), dc.met(), dc.topo(), dc.woa()

Examples

## Not run: 
library(dc)
library(oce)
# User must create directory ~/data/coastline first.
# As of September 2016, the downloaded file, named
# "ne_50m_coastline.zip", occupies 443K bytes.
filename <- dc.coastline(destdir="~/data/coastline")
coastline <- read.coastline(filename)
plot(coastline)

## End(Not run)

dankelley/dc documentation built on June 3, 2020, 8:25 a.m.