Data export formats
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The vector and gridded data sets can be exported through the GEBCO Digital
Atlas (GDA) Software Interface. Formats are included that are compatible
with the Generic Mapping Tools (GMT) system, Environment Systems Research
Institute (ESRI) and AutoCAD software packages. The following relates to export from the GDA using version 2.12 of the GDA Software Interface.
- Exporting GEBCO's gridded bathymetric data sets
- Exporting the vector data sets
For users not able to make use of the GDA Software Interface, the Centenary Edition of the GDA disc set includes a CDROM which contains a directly accessible set of files.
1. Exporting GEBCO's gridded bathymetric data sets
The complete GEBCO_2014 Grid, GEBCO_2014 Source Identifier (SID) Grid and GEBCO One Minute Grid files (or any subsets) may be
exported in a simple ASCII format or as a netCDF file. Data exported in
netCDF are suitable for use with the Generic Mapping Tools (GMT) system.
The elevation values are stored as signed 2-byte integers with the convention that bathymetric depths have negative values and topographic heights have positive values.
1.1 ASCII format
The following options are available.
Export the data in the format: longitude, latitude and elevation. Longitude and latitude formats may be selected from the following options
- decimal degrees
- degrees and decimal minutes
- degrees, minutes and decimal seconds
Export the elevation data only, as either one data point per line or one row of data per line. In the latter case, the data values may be separated by commas, spaces or output in a fixed-width format.
An additional option is available to export the data in an ASCII form that can be converted to an ESRI raster file using ESRI data conversion software. The data are exported in the form of rows with one row of data per line. The file includes header information in the required format for the conversion of the data file to an ESRI raster. The grid points are read eastwards from the Northwest corner of the selected data area.
1.2 NetCDF format
The GEBCO gridded data sets are stored in netCDF as a one dimensional array of 2-byte signed integers that represent integer elevations in metres. The data start at position 90°N 180°W and increase eastward.
2. Exporting the vector data sets
The vector data sets include bathymetric contour, coastline and trackline control data. The vectors may be exported in the following formats
- American Standard Code for Information Interchange (ASCII)
- Data Exchange Format (DXF)
- ESRI Shapefile
In the data files, latitude is stored in the range -90° to +90° with north positive and south negative. Longitude is stored in the range -180° to +180° with east positive and west negative. However, the user can specify that the longitude data are stored in the range 0° to 360°.
2.1 ASCII format
ASCII files are built up as a series of labelled vector streams relating to bathymetric contours, coastlines, tracklines, survey box outlines or sounding points. A new vector stream is started for each contour segment, coastline segment, trackline, survey box outline or isolated sounding point.
Each vector stream consists of coordinate pair records preceded by a header record containing
- a flag character, IFLAG, set to '>'
- feature code, ICODE, for the vector
- a count, ICOUNT, of the number of succeeding coordinate pairs making up the vector
Note that the '>' character was not included in previous versions of
the GDA ASCII export format. Each coordinate pair is stored in a record
with a geographic latitude 'ALAT' and longitude 'ALONG', expressed in decimal
Each 20-byte record is made up of a
Header record — IFLAG, ICODE, ICOUNT in format (A1,2I6,5X),CR,LF
Coordinate pair record — ALAT, ALONG in format (F8.4,F10.4),CR,LF
The feature code definitions are
- 0 for coastlines
- 1 for landward limit of seawater (Antarctic coastline)
- 2 for seaward limit of floating permanent ice (Antarctic coastline)
- depth in corrected metres for bathymetric contours
- 22010 for ice coastline (definite)
- 22011 for rock coastline (definite)
- 22012 for grounding line (definite)
- 22013 for rock against ice shelf (definite)
- 22020 for ice coastline (approximate)
- 22021 for rock coastline (approximate)
- 22022 for grounding line (approximate)
- 22023 for rock against ice shelf (approximate)
- 22030 for iceberg tongue
- 22040 for floating glacier tongue
- 22050 for ice shelf front
- 22090 for ice rumples (distinct)
- 22100 for ice rumples (indistinct)
- 22222 for tracklines
- 22223 for outlines of survey boxes, special compilations or areas of dense sounding coverage
- 22224 for isolated sounding point positions
Codes '1', '2', and '22010' to '22100' correspond to Antarctic related coastlines. Codes '1' and '2' are only present when the user has requested that feature codes '22010' to '22023' and '22090' and '22100' should be combined into code '1' and feature codes '22030' to '22050' into code '2'.
2.2 DXF format
DXF originated as a proprietary format in the commercially
available 'AutoCAD' package, but is now a standard input format for many
other commercially available software packages.
In DXF, the vector streams are expressed as polylines in geographic coordinates with each contour depth and coastline feature type assigned to a separate layer and a separate logical colour. Likewise, separate layers and logical colours are also assigned for tracklines, survey boxes and the position of isolated sounding points. The latter are expressed as type point rather than polylines. Each of the layers is labelled using the feature code definitions listed in the ASCII format definition above.
2.3 Shapefile format
This format is used by ESRI products such as ArcInfo.
Line and point feature types may be exported in ESRI Shapefile format. Bathymetric contour, coastline and trackline data are exported as line feature types and the position of isolated soundings as point feature types. Line and point feature types are exported to separate files.
2.4 Ordering of vectors
Vector data may be exported in ordered form. Ordering is by feature code. Thus any '0', '1' or '2' coastline vectors will appear before the bathymetric contour vectors which, in turn, will be arranged in ascending order of their depths. If present, the detailed Antarctic coastlines will follow the bathymetric contours and then be followed by tracklines, survey box outlines and isolated sounding points.
2.5 Contiguity of vectors
Within the GDA system the vector data sets are split into ten degree squares. The user can select to join up the vector segments on export. This option is only available if the user has selected to save the data in ordered format as described above.