marmap (version 1.0.10)

dist2isobath: Computes the shortest great circle distance between any point and a given isobath

Description

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.

Usage

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

Value

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.

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).

Author

Benoit Simon-Bouhet

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.

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])