MIL-PRF-89020B
3.9.1 The onc.dir file. An ASCII file named ONC.DIR provides, via ONC
tiles, a directory to the DTED cells on the CD-ROM or when downloaded from the
NIMA Gateway.
3.9.2 The <xxx>.dt0, .dt1, .dt2 files.
The .dt0, .dt1, and .dt2 are
the terrain elevation data files for DTED Level 0, DTED Level 1 and DTED Level
2, respectively. A data file of DTED is a cell defined by latitudes and
longitudes of a geographic reference system. The terrain elevation
information is expressed in meters. The locations of elevation posts are
defined by the intersections of rows and columns within a matrix. The
required matrix intervals, defined in terms of geographic arc seconds, vary
according to latitude (see TABLE I for DTED Level 0, TABLE II for DTED Level 1
and TABLE III for DTED Level 2). Each terrain elevation data file consists of
the User Header Label(UHL), Data Set Identification(DSI) Record, Accuracy
Description Record(ACC) and the Data records. (See 3.12 for details of the
terrain elevation data files.)
Note:
In the tables below, all values in seconds are in terms of arc
measure.
TABLE I.
Matrix intervals for DTED Level 0.
ZONE
LATITUDE
MATRIX
INTERVAL
latitude
longitude
I
0°
-
50°
North-South
30
x
30
seconds
II
50°
-
70°
North-South
30
x
60
seconds
III
70°
-
75°
North-South
30
x
90
seconds
IV
75°
-
80°
North-South
30
x
120
seconds
V
80°
-
90°
North-South
30
x
180
seconds
TABLE II.
Matrix intervals for DTED Level 1.
ZONE
LATITUDE
MATRIX
INTERVAL
latitude
longitude
I
0°
-
50°
North-South
3
x
3
seconds
II
50°
-
70°
North-South
3
x
6
seconds
III
70°
-
75°
North-South
3
x
9
seconds
IV
75°
-
80°
North-South
3
x
12
seconds
V
80°
-
90°
North-South
3
x
18
seconds
TABLE III.
Matrix intervals for DTED Level 2.
ZONE
LATITUDE
MATRIX
INTERVAL
latitude
longitude
I
0°
-
50°
North-South
1
x
1
seconds
II
50°
-
70°
North-South
1
x
2
seconds
III
70°
-
75°
North-South
1
x
3
seconds
IV
75°
-
80°
North-South
1
x
4
seconds
V
80°
-
90°
North-South
1
x
6
seconds
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