Mapping Toolbox

globedem

Read elevation data from GLOBE Digital Elevation Map files into a regular matrix map

Syntax

• [map,maplegend] = globedem(filename,scalefactor)
  [map,maplegend] = globedem(filename,scalefactor,latlim,lonlim)
  

[map,maplegend] = globedem(dirname,scalefactor,latlim,lonlim)

Background

GLOBE, the Global Land One-km Base Elevation data, was compiled by the National Geophysical Data Center from more than 10 different sources of gridded elevation data. GLOBE may be considered a higher resolution sucessor to TerrainBase. The dataset consists of 16 tiles, each covering 50 by 90 degrees. Tiles require as much as 60 MB of storage. Uncompressed tiles take between 100 and 130 MB.

Description

[map,maplegend] = globedem(filename,scalefactor) reads the GLOBE DEM files and returns the result as a regular matrix map. The filename is given as a string which does not include an extension. GLOBEDEM first reads the ESRI header file found in the subdirectory '/esri/hdr/' and then the binary data file filename. If the files are not found on the Matlab path, they may be selected interactively. Scalefactor is an integer, which when equal to 1 gives the data at its full resolution. When scalefactor is an integer n larger than one, every nth point is returned. The map data is returned as an array of elevations and associated regular matrix map legend. Elevations are given in meters above mean sea level using WGS 84 as a horizontal datum.

[map,maplegend] = globedem(filename,scalefactor,latlim,lonlim) allows a subset of the map data to be read. The limits of the desired data are specified as vectors of latitude and longitude in degrees. The elements of latlim and lonlim must be in ascending order.

[map,maplegend] = globedem(dirname,scalefactor,latlim,lonlim) reads and concatenates data from multiple files within a GLOBE directory tree. The dirname input is a string with the name of the directory which contains both the uncompressed files data files and the ESRI header files.

Remarks

The Mapping Toolbox reads data from GLOBE version 1.0. The data is for elevations only. Elevations are given in meters above mean sea level using WGS 84 as a horizontal datum. Areas with no data, such as the oceans, are coded with NaNs.

The data is available over the Internet via anonymous ftp from:

• <ftp://ftp.ngdc.noaa.gov/GLOBE_DEM/data/elev/>
  

The data and some documentation is also available over the World-Wide-Web from:

• <http://www.ngdc.noaa.gov/seg/topo/globe.shtml>
  

Examples

Determine which file contains the area around Cape Cod.

• latlim = [41 42.5]; lonlim = [-73 -69.9];
  globedems(latlim,lonlim)
  
  ans = 
  
      'f10g'
  

Extract every 20th point from the tile covering the northeastern United States and eastern Canada. Provide an empty file name, and select the file interactively.

• [map,maplegend] = globedem([],20);
  size(map)
  ans =
     300   540
  

Extract a subset of the data for Massachusetts at the full resolution.

• latlim = [41 42.5]; lonlim = [-73 -69.9];
  [map,maplegend] = globedem('f10g',1,latlim,lonlim);
  size(map)
  ans =
     181 373
  

Replace the NaNs in the ocean with -1 to color them blue.

• map(isnan(map)) = -1;
  

Extract some data for southern Louisiana in an area that straddles two tiles. Provide the name of the directory containing the data files, and let globedem determine which files are required, read from the files, and concatenate the data into a single regular matrix map.

• latlim =[28.61 31.31]; lonlim = [-91.24 -88.62];
  globedems(latlim,lonlim)
  
  ans = 
  
      'e10g'
      'f10g'
  
  [map,maplegend] = 
  globedem('d:\externalData\globe\elev',1,latlim,lonlim);
  size(map)
  
  ans =
  
          325.00        315.00
  
  

See Also

demdataui	Interactive tool to read digital elevation data
dted	Read Digital Terrain Elevation Data (DTED) data
gtopo30	Read GTOPO30 digital elevation data
satbath	Read global 2-minute topography from satellite bathymetry
tbase	Read data from the TerrainBase dataset
usgsdem	Read USGS digital elevation maps

References

<http://www.ngdc.noaa.gov/seg/topo/globe.shtml>

fipsname

globedems