subsetBathy function

Creates bathy objects from larger bathy objects

Generates rectangular or non rectangular bathy objects by extracting bathymetric data from larger bathy objects.

subsetBathy(mat, x, y=NULL, locator=TRUE, ...)

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.
• locator: Logical. Whether to choose data points interactively with a map or not. If TRUE (default), 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

subsetBathy allows the user to generate new bathy objects by extracting data from larger bathy objects. The extraction of bathymetric data can be done interactively by clicking on a bathymetric map, or by providing longitudes and latitudes for the boundaries for the new bathy object. If two data points are provided, a rectangular area is selected. If more than two points are provided, a polygon is defined by linking the points and the bathymetic data is extracted within the polygon only. subsetBathy relies on the point.in.polygon function from package sp to identify which points of the initial bathy matrix lie witin the boundaries of the user-defined polygon.

Returns

A matrix of class bathy.

References

Pebesma, EJ, RS Bivand, (2005). Classes and methods for spatial data in R. R News 5 (2), https://cran.r-project.org/doc/Rnews/

Bivand RS, Pebesma EJ, Gomez-Rubio V (2013). Applied spatial data analysis with R, Second edition. Springer, NY. https://asdar-book.org

Author(s)

Benoit Simon-Bouhet

See Also

plot.bathy, get.depth, summary.bathy, aleutians

Examples

# load aleutians dataset
data(aleutians)

# create vectors of latitude and longitude to define the boundary of a polygon
lon <- c(188.56, 189.71, 191, 193.18, 196.18, 196.32, 196.32, 194.34, 188.83)
lat <- c(54.33, 55.88, 56.06, 55.85, 55.23, 54.19, 52.01, 50.52, 51.71)

# plot the initial bathy and overlay the polygon
plot(aleutians, image=TRUE, land=TRUE, lwd=.2)
polygon(lon,lat)

# Use of subsetBathy to extract the new bathy object
zoomed <- subsetBathy(aleutians, x=lon, y=lat, locator=FALSE)

# plot the new bathy object
dev.new() ; plot(zoomed, land=TRUE, image=TRUE, lwd=.2)

# alternativeley once the map is plotted, use the interactive mode:
## Not run:

plot(aleutians, image=TRUE, land=TRUE, lwd=.2)
zoomed2 <- subsetBathy(aleutians, pch=19, col=3)
dev.new() ; plot(zoomed2, land=TRUE, image=TRUE, lwd=.2)
## End(Not run)

# click several times and press Escape