The GLOBE DEM data .?10g files can be imported. The GLOBE DEM data ?10s files are not supported.
File Description
GLOBE DEM stands for Global Land One-Kilometer Base Elevation (GLOBE) digital elevation model (DEM). The files are 30-arc-second (1-km) gridded, quality-controlled global digital elevation models.
GLOBE DEM is a global data set covering 180 degrees West to 180 degrees East longitude and 90 degrees North to 90 degrees South latitude. The horizontal grid spacing is 30 arc-seconds (0.008333... degrees) in latitude and longitude, resulting in dimensions of 21,600 rows and 43,200 columns. At the Equator, a degree of latitude is about 111 kilometers. GLOBE has 120 values per degree, giving GLOBE slightly better than 1 km gridding at the Equator, and progressively finer longitudinally toward the Poles. The horizontal coordinate system is seconds of latitude and longitude referenced to World Geodetic System 84 (WGS84). The vertical units represent elevation in meters above Mean Sea Level. The elevation values range from -407 to 8,752 meters on land. In GLOBE Version 1.0, ocean areas have been masked as "no data" and have been assigned a value of -500. Due to the nature of the raster structure of the DEM, small islands in the ocean less than approximately 1 square kilometer (specifically, those that are not characterized by at least one 30" grid cell and/or do not have coastlines digitized into Digital Chart of the World or World Vector Shoreline) may not be represented.
GLOBE's accuracy can be subdivided into horizontal and vertical accuracy, and again into absolute and relative accuracy. Horizontal accuracy can be affected by errors in horizontal positioning of features, or errors in recording horizontal datum. Horizontal accuracy may differ between sources. The absolute vertical accuracy of GLOBE varies by location according to the source data. Generally, areas derived from raster source data have higher accuracy than those derived from vector source data.
GLOBE is a data base, a data management philosophy, a working environment, and a file format. GLOBE began with the conceptual opening of a two-dimensional thirty-arc-second (30") latitude-longitude digital data array, and the hope to populate it with both the Best Available Data (B.A.D.), and the Globally Only Open-Access Data (G.O.O.D.). The former could include copyright data that might be made available for distribution by GLOBE with minimal restrictions, while the latter could not contain any restricted data. Allowing for both options has enabled GLOBE, for example, to work with the Australian Surveying and Land Information Group to develop a DEM much better than could otherwise be included while respecting the intellectual property rights of the Australian government.
The Global Land One-km Base Elevation Project (GLOBE) Task Team was established by the Committee on Earth Observation Satellites. It was part of Focus I of the International Geosphere-Biosphere Programme - Data and Information System.
File Format
In addition to the GLOBE .DEM file, associated files include a source/lineage file. This source/lineage file provides a mask of ocean coverage (by using category 0 of the source/lineage file), so that the user may reassign the -500 flag values for ocean coverage to 0, then later re-separate those values from 0 values on land. This is 16-bit signed integer data in a simple binary raster. There are no header or trailer bytes embedded in the image. The data are stored in row major order (all the data for row 1, followed by all the data for row 2, etc.). All files have 10800 columns, and either 4800 or 6000 rows."
The digital elevation file format has two file types. Files .?10G and .?10B ("?" is the wildcard notation for tile letters "A" through "P") are provided as 16-bit signed integer data in a simple binary raster. There are no header or trailer bytes embedded in the image. The data are stored in row major order (all the data for row 1, followed by all the data for row 2, etc.). All files have 10800 columns, and either 4800 or 6000 rows.
The following diagram depicts the organization of the files:
bytes1/2.................................bytes21599/21600 bytes21601/21602.........................bytes43199/43200 ......................................................... ......................................................... etc. ................................(last byte-1)/(last byte)
The data are in little-endian byte order (for IBM-compatible PCs, Digital Equipment VAXes, etc.) UNIX workstations using big-endian byte order can swap bytes using the command:
dd if=inputfilename of=outputfilename conv=swab
where "inputfilename" and "outputfilename" are replaced with the user’s selection of input and output file names
Listed below is the projection information for each data file in GLOBE.
Projection Geographic (latitude/longitude)
Datum WGS84
Zunits Meters above mean sea level
Hunits 30 arc-seconds of latitude and longitude
Spheroid WGS84
Xshift 0.0000000000
Yshift 0.0000000000
Cell Referencing Each cell is nominally bound by 30" intervals
of latitude and longitude, beginning with any
whole degree (e.g. 0.0000 degrees)
Parameters NONE other than those above
File Name Extensions
.DEM
Import Method
Choose the File | Import command.
Import Restrictions/Limitations
GLOBE DEM data .?10s files are not supported.
See Also