dist2isobath function

Computes the shortest great circle distance between any point and a given isobath

Computes the shortest (great circle) distance between a set of points and an isoline of depth or altitude. Points can be selected interactively by clicking on a map.

dist2isobath(mat, x, y=NULL, isobath=0, locator=FALSE, ...)

Arguments

• mat: Bathymetric data matrix of class bathy, as imported with read.bathy.
• x: Either a list of two elements (numeric vectors of longitude and latitude), a 2-column matrix or data.frame of longitudes and latitudes, or a numeric vector of longitudes.
• y: Either NULL (default) or a numerical vector of latitudes. Ignored if x is not a numeric vector.
• isobath: A single numerical value indicating the isobath to which the shortest distance is to be computed (default is set to 0, i.e. the coastline).
• locator: Logical. Whether to choose data points interactively with a map or not. If TRUE, a bathymetric map must have been plotted and both x and y are both ignored.
• ...: Further arguments to be passed to locator when the interactive mode is used (locator=TRUE).

Details

dist2isobath allows the user to compute the shortest great circle distance between a set of points (selected interactively on a map or not) and a user-defined isobath. dist2isobath takes advantage of functions from packages sp (Lines() and SpatialLines()) and geosphere (dist2Line) to compute the coordinates of the nearest location along a given isobath for each point provided by the user.

Returns

A 5-column data.frame. The first column contains the distance in meters between each point and the nearest point located on the given isobath. Columns 2 and 3 indicate the longitude and latitude of starting points (i.e. either coordinates provided as x and y or coordinates of points selected interactively on a map when locator=TRUE) and columns 4 and 5 contains coordinates (longitudes and latitudes) arrival points i.e. the nearest points on the isobath.

Author(s)

Benoit Simon-Bouhet

See Also

linesGC, lc.dist

Examples

# Load NW Atlantic data and convert to class bathy
data(nw.atlantic)
atl <- as.bathy(nw.atlantic)

# Create vectors of latitude and longitude
lon <- c(-70, -65, -63, -55, -48)
lat <- c(33, 35, 40, 37, 33)

# Compute distances between each point and the -200m isobath
d <- dist2isobath(atl, lon, lat, isobath = -200)
d

# Visualize the great circle distances
blues <- c("lightsteelblue4","lightsteelblue3","lightsteelblue2","lightsteelblue1")
plot(atl, image=TRUE, lwd=0.1, land=TRUE, bpal = list(c(0,max(atl),"grey"), c(min(atl),0,blues)))
plot(atl, deep=-200, shallow=-200, step=0, lwd=0.6, add=TRUE)
points(lon,lat, pch=21, col="orange4", bg="orange2", cex=.8)
linesGC(d[2:3],d[4:5])