oce (version 1.2-0)

download.met: Download and Cache a met File

Description

Data are downloaded from the Environment Canada's historical data website and cached locally.

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

The data are downloaded from https://climate.weather.gc.ca/historical_data/search_historic_data_e.html using utils::download.file() pointed to the Environment Canada website (reference 1) using queries that had to be devised by reverse-engineering, since the agency does not provide documentation about how to construct queries. Caution: the query format changes from time to time, so download.met() may work one day, and fail the next.

The constructed query contains Station ID, as provided in the id argument. Note that this seems to be a creation of Environment Canada, alone; it is distinct from the more standard "Climate ID" and "WMO ID". To make things more difficult, Environment Canada states that the Station ID is subject to change over time. (Whether this applies to existing data is unclear.)

Given these difficulties with Station ID, users are advised to consult the Environment Canada website (reference 1) before downloading any data, and to check it from time to time during the course of a research project, to see if the Station ID has changed. Another approach would be to use Gavin Simpson's canadaHCD package (reference 2) to look up Station IDs. 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.

References

1. Environment Canada website for Historical Climate Data http://climate.weather.gc.ca/index_e.html

2. Gavin Simpson's canadaHCD package on GitHub https://github.com/gavinsimpson/canadaHCD

See Also

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

Other functions that download files: download.amsr(), download.coastline(), download.topo()

Other things related to met data: [[,met-method, [[<-,met-method, as.met(), met-class, met, plot,met-method, read.met(), subset,met-method, summary,met-method, test_met_csv1.csv, test_met_csv2.csv, test_met_xml2.xml

Examples

# NOT RUN {
library(oce)
## Download data for Halifax International Airport, in September
## of 2003. (This dataset is used for data(met) provided with oce.)
metFile <- download.met(6358, 2003, 9, destdir=".")
met <- read.met(metFile)
# }
# NOT RUN {
# }

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