etopo - Read global 5-min or 2-min digital terrain data

Syntax

[Z, refvec] = etopo [Z, refvec] = etopo(samplefactor) [Z, refvec] = etopo(samplefactor, latlim, lonlim) [Z, refvec] = etopo(directory, ...) [Z, refvec] = etopo(file, ...)

Description

[Z, refvec] = etopo reads the ETOPO data for the entire world from the ETOPO data in the current directory. The current directory is searched first for ETOPO2 binary data, followed by ETOPO5 binary data, followed by ETOPO5 ASCII data from the file names etopo5.northern.bat and etopo5.southern.bat. Once a match is found the data is read. The data grid, Z, is returned as an array of elevations. Data values are in whole meters, representing the elevation of the center of each cell. refvec is the associated three-element referencing vector that geolocates Z.

[Z, refvec] = etopo(samplefactor) reads the data for the entire world, downsampling the data by samplefactor. samplefactor is a scalar integer, which when equal to 1 gives the data at its full resolution (1080 by 4320 values for ETOPO5 data and 5400 by 10800 values for ETOPO2 data). When samplefactor is an integer n greater than one, every n^th point is returned. samplefactor must divide evenly into the number of rows and columns of the data file. If samplefactor is omitted or empty, it defaults to 1.

[Z, refvec] = etopo(samplefactor, latlim, lonlim) reads the data for the part of the world within the specified latitude and longitude limits. The limits of the desired data are specified as two-element vectors of latitude, latlim, and longitude, lonlim, in degrees. The elements of latlim and lonlim must be in ascending order. lonlim must be specified in the range [0 360] for ETOPO5 data and [-180 180] for ETOPO2 data. If latlim is empty the latitude limits are [-90 90]. If lonlim is empty, the longitude limits are determined by the file type.

[Z, refvec] = etopo(directory, ...) allows the path for the ETOPO data file to be specified by directory rather than the current directory.

[Z, refvec] = etopo(file, ...) reads the ETOPO data from file, where file is a string or a cell array of strings containing the name or names of the ETOPO data files.

Background

ETOPO5 is a global database of elevations and depths on a regular 5-minute grid. It is a compilation of data from a variety of different sources, including the U.S. Naval Oceanographic Office, U.S. Defense Mapping Agency, U.S. Navy Fleet Numerical Oceanographic Center, Bureau of Mineral Resources, Australia, and the Department of Industrial and Scientific Research, New Zealand. These databases were assembled by Margo Edwards at Washington University, St. Louis, Missouri.

Remarks

ETOPO5 data values are in whole meters, representing the elevation of the center of each cell. Some parts of the world are represented by data with a horizontal resolution as coarse as 1 degree by 1 degree. The vertical resolution varies from 1 meter for Australia and New Zealand to as much as 150 meters for parts of Africa, Asia, and South America. Oceanographic data in areas shallower than 200 meters contains little detail, because of how depth contours were converted to gridded depths.

ETOPO5 is superseded by ETOPO2 and the TerrainBase digital terrain model. See the tbase external interface function for more information.

Note You can find links to more information about ETOPO files in the following page at the MathWorks Web site: http://www.mathworks.com/support/tech-notes/2100/2101.html.

Examples

Example 1

% Read and display the ETOPO5 data from the directory 'etopo5'
% downsampled by a factor of 10.
[Z, refvec] = etopo('etopo5',10);
whos

  Name         Size                    Bytes  Class
  Z          216x432                  746496  double array
  refvec       1x3                        24  double array

Grand total is 93315 elements using 746520 bytes

axesm robinson
geoshow(Z, refvec, 'DisplayType', 'surface');
colormap(demcmap(Z));

Example 2

% From the current directory, read and display the 
% ETOPO2 binary data downsampled by a factor of 10.
cd etopo2
[Z, refvec] = etopo('ETOPO2.dos.bin', 10);
whos

  Name         Size                    Bytes  Class
  Z          540x1080                4665600  double array
  refvec       1x3                        24  double array

figure; axesm robinson
geoshow(Z, refvec, 'DisplayType', 'surface');
colormap(demcmap(Z));