webtide {oce} | R Documentation

## 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.

### 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.

### 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.

### Author(s)

Dan Kelley

### 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

    ## Not run:
    library(oce)
    prediction <- webtide("predict", longitude=-69.61, latitude=48.14)

    ## End(Not run)

[Package oce version 0.9-18 Index]