get.transect function

Compute approximate cross section along a depth transect

Compute the depth along a linear transect which bounds are specified by the user.

get.transect(mat, x1, y1, x2, y2, locator=FALSE, distance=FALSE, ...)

Arguments

• mat: bathymetric data matrix of class bathy, imported using read.bathy (no default)
• x1: start longitude of the transect (no default)
• x2: stop longitude of the transect (no default)
• y1: start latitude of the transect (no default)
• y2: stop latitude of the transect (no default)
• locator: whether to use locator to choose transect bounds interactively with a map (default is FALSE)
• distance: whether to compute the haversine distance (in km) from the start of the transect, along the transect (default is FALSE)
• ...: other arguments to be passed to locator() to specify the characteristics of the points and lines to draw on the bathymetric map when locator=TRUE.

Details

get.transect allows the user to compute an approximate linear depth cross section either by inputing start and stop coordinates, or by clicking on a map created with plot.bathy. In its interactive mode, this function uses the locator function (graphics package); after creating a map with plot.bathy, the user can click twice to delimit the bound of the transect of interest (for example, lower left and upper right corners of a rectangular area of interest), press Escape, and get a table with the transect information.

Returns

A table with, at least, longitude, latitude and depth along the transect, and if specified (distance=TRUE), the distance in kilometers from the start of the transect. The number of elements in the resulting table depends on the resolution of the bathy object.

Note

The distance option of get.transect is calculated based on the haversine formula for getting the great circle distance (takes into account the curvature of the Earth). get.transect uses an internal function called diag.bathy that extracts the approximate diagonal of a matrix, when that matrix has uneven dimentions (different numbers of columns and rows).

Author(s)

Eric Pante and Benoit Simon-Bouhet

Warning

Clicking once or more than twice on the map will return a warning message: "Please choose only two points from the map". Manually entering coordinates that are outside the geographical range of the input bathy matrix will return a warning message.

See Also

read.bathy, nw.atlantic, nw.atlantic.coast, get.depth, get.sample

Examples

# load datasets
        data(nw.atlantic); as.bathy(nw.atlantic) -> atl
        data(nw.atlantic.coast)

# Example 1. get.transect(), without use of locator()
        get.transect(atl, -65, 43,-59,40) -> test ; plot(test[,3]~test[,2],type="l")
        get.transect(atl, -65, 43,-59,40, distance=TRUE) -> test ; plot(test[,4]~test[,3],type="l")

# Example 2. get.transect(), without use of locator(); pretty plot
        par(mfrow=c(2,1),mai=c(1.2, 1, 0.1, 0.1))
        plot(atl, deep=-6000, shallow=-10, step=1000, lwd=0.5, col="grey50",drawlabels=TRUE)
        lines(nw.atlantic.coast)

        get.transect(atl, -75, 44,-46,32, loc=FALSE, dis=TRUE) -> test
        points(test$lon,test$lat,type="l",col="blue",lwd=2,lty=2)
        plotProfile(test)

# Example 3. get.transect(), with use of locator(); pretty plot
## Not run:

        par(mfrow=c(2,1),mai=c(1.2, 1, 0.1, 0.1))
        plot(atl, deep=-6000, shallow=-10, step=1000, lwd=0.5, col="grey50",drawlabels=TRUE)
        lines(nw.atlantic.coast)
        
        get.transect(atl, loc=TRUE, dis=TRUE, col=2, lty=2) -> test
        plotProfile(test)
## End(Not run)