Digital Terrain Elevation Data (DTED) from the US Military, published by the National Geospatial-Intelligence Agency (NGA), formerly known as NIMA. DTED is published in three levels: Level 0 with a file extension of .dt0 and a resolution of approximately 900 meters, Level 1 with a file extension of .dt1 and a resolution of approximately 90 meters, and Level 2 with a file extension of .dt2 and a resolution of approximately 30 meters, In theory, Level 1 and Level 2 data are not available outside of the US Department of Defense and approved contractors.
In practise, restrictions on Level 1 and Level 2 data do not matter since most GIS practitioners feel that Space Shuttle SRTM data and ASTER data, with a resolution of 30 meters, are better quality.
The Manifold dataport reads Level 0, Level 1 and Level 2 data, and automatically extracts coordinate system information to assign the coordinate system for imported images.
To import from DTED format:
Choose File-Import from the main menu.
In the Import dialog browse to the folder containing data of interest.
Double-click the file ending in .dt0 or .dt1 or .dt2 for the data of interest.
A table and an image will be created.
We can double-click on images that are created to view them. For a more interesting display, we first create a new data source using a Bing street maps image server as shown in the Example: An Imageserver Tutorial topic. We then create a map and drag and drop the Bing layer into the map, and then we drag and drop the image into the map.
The image appears using the correct projection, but it is still in a default monochrome tone. We must use the Style pane to assign a palette to color the elevation values in the image.
We use the Style pane to color the image using a palette and we apply hill shading, as seen above.
That provides a much better display. In the illustration above, we have added a transparent streets Google image server layer above the terrain elevation image, to provide better context. The display shows terrain elevation values near Waco, Texas, with approximately 60 meter resolution per pixel.
Example: Spectacular Images and Data from Web Servers
Example: An Imageserver Tutorial