makeTopography function

Make Topography Data from Online Source

Make topography data suitable for the 'graphics::contour' and 'grDevices::contourLines' functions using freely available global seafloor topography data.

makeTopography (dat, digits=2, func=NULL)

Arguments

• dat: data.frame -- data with three optionally-named columns: x, y, and z. The columns must appear in that order.
• digits: numeric -- integer indicating the precision to be used by the function round on (x,y) values.
• func: function -- to summarize z if (x,y) points are duplicated. Defaults to mean() if no function is specified.

Details

Suitable data can be obtained through the Topex acquisition form. The function 'utils::read.table' will import dowloaded ASCII files into R, creating objects suitable for the argument 'dat' in 'makeTopography'.

When creating data for regions with longitude values spanning -180$degrees$ to 0$degrees$, consider subtracting 360 from the result's longitude coordinates (x).

When creating bathymetry data, consider negating the result's elevations (z) to give depths positive values.

Combinations of (x,y) do not need to be complete (z[x,y]=NA) or unique (z[x,y] = func(z[x,y])).

Returns

List with elements x, y, and z. Elements x and y are vectors, while z is a matrix with rownames x

and colnames y. The functions 'graphics::contour' and 'grDevices::contourLines'

expect data conforming to this list format.

See Also

In package graphics:

contour

In package grDevices:

contourLines

In package PBSmapping:

convCP

Author(s)

Nicholas M. Boers, Staff Software Engineer

Jobber, Edmonton AB

Maintainer: Rowan Haigh, Program Head -- Offshore Rockfish

Pacific Biological Station (PBS), Fisheries & Oceans Canada (DFO), Nanaimo BC

locus opus: Institute of Ocean Sciences (IOS), Sidney BC

Last modified Rd: 2021-01-11

Examples

local(envir=.PBSmapEnv,expr={
  oldpar = par(no.readonly=TRUE)
  #--- Example 1: Sample data frame and conversion.
  file <- data.frame(X=c(1,1,2,2),Y=c(3,4,3,4),Z=c(5,6,7,8))
  print(makeTopography(file))

  #--- Example 2: Aleutian Islands bathymetry
  isob <- c(100,500,1000,2500,5000)
  icol <- rgb(0,0,seq(255,100,len=length(isob)),max=255)
  afile <- paste(system.file(package="PBSmapping"),
    "/Extra/aleutian.txt",sep="")
  aleutian <- read.table(afile, header=FALSE, col.names=c("x","y","z"))
  aleutian$x <- aleutian$x - 360
  aleutian$z <- -aleutian$z
  alBathy <- makeTopography(aleutian)
  alCL <- contourLines(alBathy,levels=isob)
  alCP <- convCP(alCL)
  alPoly <- alCP$PolySet
  attr(alPoly,"projection") <- "LL"
  plotMap(alPoly, type="n", cex.axis=1.2, cex.lab=1.5)
  addLines(alPoly,col=icol)
  data(nepacLL,envir=.PBSmapEnv)
  addPolys(nepacLL,col="gold")
  legend(x="topleft",bty="n",col=icol,lwd=2,legend=as.character(isob))
  par(oldpar)
})