getNOAA.bathy: Import bathymetric data from the NOAA server

Description

Imports bathymetric data from the NOAA server, given coordinate bounds and resolution.

Usage

getNOAA.bathy(lon1,lon2,lat1,lat2, resolution = 4, keep=FALSE, antimeridian=FALSE)

Arguments

lon1

first longitude of the area for which bathymetric data will be downloaded

lon2

second longitude of the area for which bathymetric data will be downloaded

lat1

first latitude of the area for which bathymetric data will be downloaded

lat2

second latitude of the area for which bathymetric data will be downloaded

resolution

resolution of the grid, in minutes (default is 4)

keep

whether to write the data downloaded from NOAA into a file (default is FALSE)

antimeridian

whether the area should include the antimeridian (longitude 180 or -180). See details.

Value

The output of getNOAA.bathy is a matrix of class bathy, which dimensions depends on the resolution of the grid uploaded from the NOAA server. The class bathy has its own methods for summarizing and ploting the data. If keep=TRUE, a csv file containing the downloaded data is produced. This file is named using the following format: 'marmap_coord_COORDINATES_res_RESOLUTION.csv' (COORDINATES separated by semicolons, and the RESOLUTION in degrees).

Details

getNOAA.bathy queries the ETOPO1 database hosted on the NOAA website, given the coordinates of the area of interest and desired resolution. Users have the option of directly writing the downloaded data into a file (keep=TRUE argument ; see below). If an identical query is performed (i.e. using identical lat-long and resolution), getNOAA.bathy will load data from the file previously written to the disk instead of querying the NOAA database. This behavior should be used preferentially (1) to reduce the number of uncessary queries to the NOAA website, and (2) to reduce data load time. If the user wants to make multiple, identical queries to the NOAA website without loading the data written to disk, the data file name must be modified by the user. Alternatively, the data file can be moved outside of the present working directory.

getNOAA.bathy allows users to download bathymetric data in the antimeridian region when antimeridian=TRUE. The antimeridian is the 180th meridian and is located about in the middle of the Pacific Ocean, east of New Zealand and Fidji, west of Hawaii and Tonga. For a given pair of longitude values, e.g. -150 (150 degrees West) and 150 (degrees East), you have the possibility to get data for 2 distinct regions: the area centered on the antimeridian (60 degrees wide, when antimeridian=TRUE) or the area centered on the prime meridian (300 degrees wide, when antimeridian=FALSE). It is recommended to use keep=TRUE in combination with antimeridian=TRUE since gathering data for an area around the antimeridian requires two distinct queries to NOAA servers.

References

Amante, C. and B. W. Eakins, ETOPO1 1 Arc-Minute Global Relief Model: Procedures, Data Sources and Analysis. NOAA Technical Memorandum NESDIS NGDC-24, 19 pp, March 2009. http://www.ngdc.noaa.gov/mgg/global/relief/ETOPO1/docs/ETOPO1.pdf

Examples

Run this code

# NOT RUN {
# you must have an internet connection. This line queries the NOAA ETOPO1 database 
# for data from North Atlantic, for a resolution of 10 minutes. 

getNOAA.bathy(lon1=-20,lon2=-90,lat1=50,lat2=20, resolution=10) -> a
plot(a, image=TRUE, deep=-6000, shallow=0, step=1000)

# download speed for a matrix of 10 degrees x 10 degrees x 30 minutes
system.time(getNOAA.bathy(lon1=0,lon2=10,lat1=0,lat2=10, resolution=30))
# }

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