Get a tidal prediction from a WebTide database. This only works if the standalone WebTide application is installed, and if it is installed in a standard location. The details of installation are not within the oce purview.
Source
The WebTide software may be downloaded for free at the
Department of Fisheries and Oceans (Canada) website at
http://www.bio.gc.ca/science/research-recherche/ocean/webtide/index-en.php
(checked February 2016 and May 2017).
Arguments
- action
An indication of the action, either
action="map"
to draw a map oraction="predict"
to get a prediction; see “Details”.- longitude, latitude
optional location at which prediction is required (ignored if
node
is given).- node
optional integer relating to a node in the database. If
node
is given, then neitherlatitude
norlongitude
may be given. Ifnode
is positive, then specifies indicates the node. If it is negative,locator()
is called so that the user can click (once) on the map, after which the node is displayed on the map.- time
a vector of times (in the UTC timezone) at which prediction is to be made. If not supplied, this will be the week starting at the present time, computed with
presentTime()
, with a 15 minute increment.- basedir
directory containing the
WebTide
application. For example, the author uses"/usr/local/WebTide"
for this value, because that is where he installed the webtide materials, e.g. "/usr/local/WebTide/data/nwatl"` is where his North Atlantic data files reside.- 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, andsshelf
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. (Seestrptime()
for the format used.)- pch
integer giving the character code (default is 20, for a bullet), used if a map-style plot is requested.
- cex
numeric giving the character expansion factor (default is 0.5), used if a map-style plot is requested.
- nodecol
colour to be used for dots on a map-style plot.
- landcol
colour of land, used in plotting maps. The default is a semi-transparent tan colour. Set to
"transparent"
to NULL to skip the drawing of land.- 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, settingdebug=0
turns off the printing, while higher values suggest that more information be printed. If one function calls another, it usually reduces the value ofdebug
first, so that a user can often obtain deeper debugging by specifying higherdebug
values.- ...
optional arguments passed to plotting functions. A common example is to set
xlim
andylim
, to focus a map region.
Value
The value depends on action
:
If
action="map"
the return value is an indication of the location of a selected node, or (ifnode
is NULL) of all nodes.If
action="predict"
, the return value is a list containing a vector of times (time
), as well as vectors of the predictedelevation
in metres and the predicted horizontal components of velocity,u
andv
, along with thenode
number, and thebasedir
andregion
as supplied to this function. Ifplot
isFALSE
, this value is returned invisibly.
Details
There are two methods of using this function. Case 1: action="map"
. In
this case, if plot
is FALSE
, a data frame is returned, containing all the
node
s in the selected database, along with all the latitude
s and
longitude
s. This value is also returned (silently) if plot
is true, but
in that case, a plot is drawn to indicate the node locations. If latitude
and longitude
are given, then the node nearest that spot is indicated on
the map; otherwise, if node
is given, then the location of that node is
indicated. There is also a special case: if node
is negative and
interactive()
is TRUE
, then locator()
is called, and the node nearest
the spot where the user clicks the mouse is indicated in the plot and in the
return value.
Case 2: action="predict"
. If plot
is FALSE
, then a list is returned,
indicating time
, predicted elevation
, velocity components u
and v
,
node
number, the name of the basedir
, and the region
. If plot
is
TRUE
, this list is returned silently, and either a map or a set of three
time-series plots (for u, v and water level) is plotted. (In the
second case, users may wish to call par(mfrow=c(3,1))
first.)
Caution
WebTide is not an open-source application, so the present function was designed based on little more than guesses about the WebTide file structure. Users should be on the lookout for odd results.
Sample of Usage
# needs WebTide at the system level
library(oce)
# 1. prediction at Halifax NS
longitude <- -63.57
latitude <- 44.65
prediction <- webtide("predict", longitude=longitude, latitude=latitude)
mtext(paste0("prediction at ", latitude, "N and ", longitude, "E"), line=0.75, side=3)
# 2. map
webtide(lon=-63.57,lat=44.65,xlim=c(-64,-63),ylim=c(43.0,46))
See also
Other things related to tides:
[[,tidem-method
,
[[<-,tidem-method
,
as.tidem()
,
plot,tidem-method
,
predict.tidem()
,
summary,tidem-method
,
tidalCurrent
,
tidedata
,
tidem
,
tidem-class
,
tidemAstron()
,
tidemVuf()