marmap (version 1.0.10)

readGEBCO.bathy: Read bathymetric data from a GEBCO file

Description

Imports 30-sec and 1-min bathymetric data from a .nc file downloaded on the GEBCO website.

Usage

readGEBCO.bathy(file, resolution = 1, sid = FALSE)

Value

The output of readGEBCO.bathy is a matrix of class bathy, which dimensions depends on the resolution specified (one-minute, the original GEBCO resolution, is the default). The class bathy has its own methods for summarizing and ploting the data.

Arguments

file

name of the .nc file

resolution

resolution of the grid, in units of the selected database (default is 1; see details)

sid

logical. Is the data file containing SID information?

Author

Eric Pante and Benoit Simon-Bouhet

Details

readGEBCO.bathy reads a 30 arcseconds or 1 arcminute bathymetry file downloaded from the GEBCO (General Bathymetric Chart of the Oceans) website (British Oceanographic Data Center). The website allows the download of bathymetric data in the netCDF format. readGEBCO.bathy uses the ncdf4 package to load the data into R, and parses it into an object of class bathy.

Data can be downloaded from the 30 arcseconds database (GEBCO_08) or the 1 arcminute database (GEBCO_1min, the default). A third database type, GEBCO_08 SID, is available from the website. This database includes a source identifier specifying which grid cells have depth information based on soundings ; it does not include bathymetry or topography data. readGEBCO.bathy can read this type of database when sid is set to TRUE. Then only the SID information will be included in the object of class bathy. Therefore, to display a map with both the bathymetry and the SID information, you will have to download both datasets from GEBCO, and import and plot both independently.

The argument resolution specifies the resolution of the object of class bathy. Because the resolution of GEBCO data is rather fine, we offer the possibility of downsizing the dataset with resolution. resolution is in units of the selected database: in "GEBCO_1min", resolution is in minutes; in "GEBCO_08", resolution is in 30 arcseconds (that is, resolution = 3 corresponds to 3x30sec, or 1.5 arcminute).

References

British Oceanographic Data Center: General Bathymetric Chart of the Oceans gridded bathymetric data sets (accessed July 10, 2020) https://www.bodc.ac.uk/data/hosted_data_systems/gebco_gridded_bathymetry_data/

General Bathymetric Chart of the Oceans website (accessed Oct 5, 2013) https://www.gebco.net

David Pierce (2019). ncdf4: Interface to Unidata netCDF (Version 4 or Earlier) Format Data Files. R package version 1.17. https://cran.r-project.org/package=ncdf4

See Also

getNOAA.bathy, read.bathy, plot.bathy

Examples

if (FALSE) {
# This example will not run, and we do not provide the dummy "gebco_file.nc" file,
# because a copyright license must be signed on the GEBCO website before the data can be
# downloaded and used. We just provide this line as an example for synthax.
  readGEBCO.bathy(file="gebco_file.nc", resolution=1) -> nw.atl

# Second not-run example, with GEBCO_08 and SID:
  readGEBCO.bathy("gebco_08_7_38_10_43_corsica.nc") -> med
  summary(med) # the bathymetry data

  readGEBCO.bathy("gebco_SID_7_38_10_43_corsica.nc")-> sid
  summary(sid) # the SID data

  colorRampPalette(c("lightblue","cadetblue1","white")) -> blues # custom col palette
  plot(med, n=1, im=T, bpal=blues(100)) # bathymetry

  as.numeric(rownames(sid)) -> x.sid
  as.numeric(colnames(sid)) -> y.sid
  contour(x.sid, y.sid, sid, drawlabels=FALSE, lwd=.1, add=TRUE) # SID
}