Obtaining DEM from ORNL DAAC
These instructions indicate how to obtain a digital elevation map (DEM) from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). They provide DEMs suitable for use in GenGIS through a web service which follows the Open Geospatial Consortium (OGC) standards. To obtain a custom DEM for your project:
- Goto ORNL DACC.
- Select the Shuttle Radar Topography Mission (SRTM) Near-global Digital Elevation Models (DEMs) dataset. You can alternatively use the lower resolution Global 30 Arc-Second Elevation Data Set (GTOPO30) dataset.
- Draw a bounding box on the world map corresponding to the region you are interested in. Alternatively, you can explicitly enter the spatial extents.
- Change the file format to GeoTIFF (INT16).
- For maps covering large areas you will also want to change the resolution. The resolution is specified in degrees. The default value of 0.00833 degrees (30-arc seconds) is approximately 1 km. The maximum resolution for the SRTM dataset is 1-arc-second (approximately 30 meters) although ORNL DACC is limited to 1 km resolution. However, the practical limit will typically be determined by your graphics card. We do not recommend loading files larger than 10MB into GenGIS as this will stress even high-end systems.
- The downloaded file will be given the name wcs. We recommend you rename this to something meaningful and give it an extension of '.tiff'.
- Note: your web browser may be setup to automatically display tiff files. If this is the case, you need to change your browser settings so you are given the choice to download such files.