GTOPO30
format
The GTOPO30 format is actually a file in raw binary format, but with a .DEM extension, that is being distributed by the United States Geological Service (USGS). The GTOPO30 files are a set of elevation data at 30 arc-seconds (about 900 meters at the equator), with global coverage and available at no charge from the USGS. A header file is required to open the file. A third file with coordinate system information is optional.
| General |
A 16-bit raw binary file with a .DEM extension of elevation. Global coverage is provided in multiple tiles of 40 degrees of longitude by 50 degrees of latitude. |
| Read |
The driver reads the files without any complications. Please note that the conversion procedure for ArcInfo users outlined in the README file that comes with the download does NOT apply to DSpatial, as DSpatial natively works with signed 16-bit data. A header file with the same name as the data file but with a .HDR extension is required. See the raw binary format description for additional information. |
| Write |
Writing of GTOPO30 data is not supported. |
| Attributes | This format does not include any attributes. |
| Coordinate system |
If, when reading, a file with the same name as the data file but with a .PRJ extension is found, this file is parsed for coordinate system information. This information needs to be in the ESRI PRJ format. If no such file is found, or if the parsing is unsuccessful, a local coordinate system is assigned. |
| Documentation | The GTOPO30 site at USGS. |
| Data sources | The files are distributed by the USGS through anonymous FTP download. The FTP server is notoriously slow and connections may fail repeatedly. |
| Developer information |
See the raw binary format description. |