oce (version 0.9-18)

webtide: Get a tidal prediction from a WebTide database

Description

Get a tidal prediction from a WebTide database

Usage

webtide(action=c("map", "predict"),
        longitude, latitude, node, time,
        basedir=getOption("webtide"),
        region="nwatl", plot=TRUE,
        tformat, debug=getOption("oceDebug"), ...)

Arguments

action

An indication of the action, either action="map" to draw a map or action="predict" to get a prediction; see Details.

longitude

longitude at which prediction is required (ignored if node is given).

latitude

latitude at which prediction is required (ignored if node is given).

node

node to look up; only needed if longitude and latitude are not given.

time

times at which prediction is to be made. If not supplied, this will be the week starting at the present time, incrementing by 15 minutes.

basedir

directory containing the WebTide application.

region

database region, given as a directory name in the WebTide directory. For example, h3o is for Halifax Harbour, nwatl is for the northwest Atlantic, and sshelf is for the Scotian Shelf and Gulf of Maine.

plot

boolean indicating whether to plot.

tformat

optional argument passed to oce.plot.ts, for plot types that call that function. (See strptime for the format used.)

debug

a debugging flag; set higher for more debugging and 0 for no debugging

...

optional arguments passed to plotting functions. A common example is to set xlim and ylim, to focus a map region.

Value

• If action="map" and plot=TRUE, the return value is a list containing the index of the nearest node, along with the latitude and longitude of that node. If action="map" and plot=FALSE, the return value is a list of all nodes, longitude, and latitudes. If action="predict", the return value is a list containing a vector of times (time), as well as vectors of the predicted elevation in metres and the predicted horizontal components of velocity, u and v, along with the node number, and the basedir and region as supplied to this function.

concept

tide

Details

If action="map" then a map is drawn, with a dot for the lower-left corner of each triangle used in the finite-element tidal simulation upon which WebTide predictions are based. If node is missing, then locator is called, so that the user can indicate a spot of interest on the map, and this point is indicated on the map (and in the return value). If node is provided, however, the point is indicated but locator is not called. (This second style is of use in documenting interactive work after the fact.) If action="predict" then either a node number or the longitude and latitude must be specified. If plot=TRUE (the default) then a plot is drawn, but no plot is produced otherwise. In either case, the (silent) return value is a list as described in the next section. The times used for prediction are specified with the time argument, and if this is not specified then a week following the present time is used.

Naturally, webtide will not work unless WebTide has been installed on the computer.

References

The WebTide software may be downloaded for free at the Department of Fisheries and Oceans (Canada) website, which in February 2016 was http://www.bio.gc.ca/science/research-recherche/ocean/webtide/index-en.php, although this site seems not to be particularly static. Note that WebTide is not an open-source application, as it consists mainly of compiled Java code, which precludes examination of the source. The present function relies on a certain structure of the WebTide data files, and since the WebTide source is closed, this was done partly by guessing. This means that the present function is brittle to changes in WebTide; users should be on the lookout for odd results.

Examples

library(oce)
prediction <- webtide("predict", longitude=-69.61, latitude=48.14)