DTED

The National Geospatial-Intelligence Agency (NGA) DTED (Digital Terrain Elevation Data) level 1 and level 2 format is supported by the GDB library for import, update and export.

The GDB layer supports the CD-ROM DTED format (as defined in MIL-PRF-89020A). Under the specification, these files have an extension .dt1, or .dt2. They contain a user header label, data set identification record, accuracy description record, and the digital elevation information. The CD-ROM DTED format also implies a hierarchical arrangement of files based on georeferencing. The GDB layer does not understand this hierarchy and only knows how to read a single DTED file at a time.

A DTED file covers a 1 degree by 1 degree area, but its resolution varies depending on the latitude of the file, and the level of the format.

DTED files contain one 16-bit signed channel of elevation data and no auxiliary data. The LONG/LAT WGS84(D000) georeferencing bounds for the elevation data are preserved. Note that the bounds are slightly larger than the 1degree x 1degree cell the file represents as the edge pixels of the data set are centered on the cell boundaries. Treated as an area, these extend slightly overlap the cell boundaries. Adjacent DTED files will shared one row, or column of values on their common border.

Export of DTED files is supported. These files are exported with a type of "DTD". Only one channel may be exported to the DTED files. Export of the HDR section of the file is optional. Some DTED readers, such as GlobalMapper, FalconView (tm) and MICRODEM, do not support the HDR section, so the HDR section is only created when the HDR export option is used.

DTED files georeferencing must exactly match a cell boundary, and will be automatically adjusted if inappropriate georeferencing is written. If a DTED file is created with a name matching the cell naming conventions (e.g. "e001n010.dt1") then the georeferencing of the cell will be automatically applied.

DTED files must match one of a limited set of configuration which will determine the level of the file. According to the standards these resolutions are appropriate to particular latitudes.

DTEDLVL    Latitude           Long/Lat Res. (arc seconds)   Pixels/Lines
-------    --------           ---------------------------   ------------
   1       0-50  (north/south)     3  x  3                  1201 x 1201
   1       50-70 (north/south)     3  x  6                  1201 x 601
   1       70-75 (north/south)     3  x  9                  1201 x 401
   1       75-80 (north/south)     3  x  12                 1201 x 301
   1       80-90 (north/south)     3  x  18                 1201 x 201
   2       0-50  (north/south)     1  x  1                  3601 x 3601
   2       50-70 (north/south)     1  x  2                  3601 x 1801
   2       70-75 (north/south)     1  x  3                  3601 x 1201
   2       75-80 (north/south)     1  x  4                  3601 x 901
   2       80-90 (north/south)     1  x  6                  3601 x 601

Because of the difficulty of creating and writing to DTED cell files appropriately, it is recommended that you use the DTEDWRIT EASI task to write the DTED cell files related to a source DEM.