Topographic data are downloaded from a data server that holds the ETOPO1 dataset (Amante, C. and B.W. Eakins, 2009), and saved as a netCDF file whose name specifies the data request, if a file of that name is not already present on the local file system. The return value is the name of the data file, and its typical use is as the filename for a call to read.topo(). Given the rules on file naming, subsequent calls to download.topo with identical parameters will simply return the name of the cached file, assuming the user has not deleted it in the meantime. Note that download.topo uses the "terra" and "ncdf4" packages, so an error is reported if they are not available.

download.topo(
west,
east,
south,
north,
resolution = 4,
destdir = ".",
destfile,
format,
server = "https://gis.ngdc.noaa.gov",
debug = getOption("oceDebug")
)

## Arguments

west, east

numeric values for the limits of the data-selection box, in degrees. These are converted to the -180 to 180 degree notation, if needed. Then, west is rounded down to the nearest 1/100th degree, and east is rounded up to the the nearest 1/100th degree. The results of these operations are used in constructing the query for the NOAA data server.

south, north

latitude limits, treated in a way that corresponds to the longitude limits.

resolution

numeric value of grid spacing, in geographical minutes. The default value is 4 minutes, corresponding to 4 nautical miles (approx. 7.4km) in the north-south direction, and less in the east-west direction.

destdir

Optional string indicating the directory in which to store downloaded files. If not supplied, "." is used, i.e. the data file is stored in the present working directory.

destfile

Optional string indicating the name of the file. If not supplied, the file name is constructed from the other parameters of the function call, so subsequent calls with the same parameters will yield the same result, thus providing the key to the caching scheme.

format

Deprecated, and ignored, as of June 2020.

server

character value specifying the base from which a download URL will be constructed. It is unlikely that any value other than the default will work, unless it is a similarly-constructed mirrored site.

debug

an integer specifying whether debugging information is to be printed during the processing. This is a general parameter that is used by many oce functions. Generally, setting debug=0 turns off the printing, while higher values suggest that more information be printed. If one function calls another, it usually reduces the value of debug first, so that a user can often obtain deeper debugging by specifying higher debug values.

## Details

The specified longitude and latitude limits are rounded to 2 digits (corresponding to a footprint of approximately 1km), and these are used in the server request. If the resultant request would generate under 1 row or column in the result, download.topo generates an error message and stops.

## Historical note relating to NOAA server changes

2022 November 13: updated to new NOAA database, with 1/4-minute resolution (a marked improvement over the previous 1-minute resolution). The revision was framed along similar changes to marmap::getNOAAbathy() made earlier today. Thanks to Clark Richards for pointing this out!

2020 May 31: updated for a change in the NOAA query structure, taking hints from marmap::getNOAAbathy().

## References

• Amante, C. and B.W. Eakins, 2009. ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-24. National Geophysical Data Center, NOAA. doi:10.7289/V5C8276M

Other functions that download files: download.amsr(), download.coastline(), download.met()

Other things related to topo data: [[,topo-method, [[<-,topo-method, as.topo(), plot,topo-method, read.topo(), subset,topo-method, summary,topo-method, topo-class, topoInterpolate(), topoWorld

Dan Kelley

## Examples

if (FALSE) {
library(oce)