Download and Cache a met File

download.met() attempts to download data from Environment Canada's historical-data website, and to cache the files locally. Lacking a published API, this function must rely on reverse-engineering of queries handled by that web server. For that reason, it is brittle.

Usage

download.met(
  id,
  year,
  month,
  deltat,
  type = "xml",
  destdir = ".",
  destfile,
  force = FALSE,
  quiet = FALSE,
  debug = getOption("oceDebug")
)

Arguments

id: A number giving the "Station ID" of the station of interest. If not provided, id defaults to 6358, for Halifax International Airport. See “Details”.
year: A number giving the year of interest. Ignored unless deltat is "hour". If year is not given, it defaults to the present year.
month: A number giving the month of interest. Ignored unless deltat is "hour". If month is not given, it defaults to the present month.
deltat: Optional character string indicating the time step of the desired dataset. This may be "hour" or "month". If deltat is not given, it defaults to "hour".
type: String indicating which type of file to download, either "xml" (the default) for an XML file or "csv" for a CSV file.
destdir: Optional string indicating the directory in which to store downloaded files. If not supplied, "." is used, i.e. the data file is stored in the present working directory.
destfile: Optional string indicating the name of the file. If not supplied, the file name is constructed from the other parameters of the function call, so subsequent calls with the same parameters will yield the same result, thus providing the key to the caching scheme.
force: Logical value indicating whether to force a download, even if the file already exists locally.
quiet: Logical value passed to download.file(); a TRUE value silences output.
debug: an integer specifying whether debugging information is to be printed during the processing. This is a general parameter that is used by many oce functions. Generally, setting debug=0 turns off the printing, while higher values suggest that more information be printed. If one function calls another, it usually reduces the value of debug first, so that a user can often obtain deeper debugging by specifying higher debug values.

Value

String indicating the full pathname to the downloaded file.

Details

If this function fails, users might try using Gavin Simpson's canadaHCD package (reference 2). This package maintains a copy of the Environment Canada listing of stations, and its find_station() function provides an easy way to determine Station IDs. After that, its hcd_hourly function (and related functions) make it easy to read data. These data can then be converted to the met class with as.met(), although doing so leaves many important metadata blank.

Sample of Usage


library(oce)
# Download data for Halifax International Airport, in September
# of 2003. This dataset is used for data(met) provided with oce.
# Note that requests for data after 2012 month 10 yield all
# missing values, for reasons unknown to the author.
metFile <- download.met(6358, 2003, 9, destdir=".")
met <- read.met(metFile)

References

Environment Canada website for Historical Climate Data https://climate.weather.gc.ca/index_e.html
Gavin Simpson's canadaHCD package on GitHub https://github.com/gavinsimpson/canadaHCD

Author

Dan Kelley