MIL-PRF-89020B3.10.5 Data record sequence. Within a <strong>data</strong> file, the <strong>data</strong> records arearranged by ascending (west to east) longitude.3.10.6 Data Block Checksum. The last four bytes of each <strong>data</strong> recordcontains a 32-bit checksum value. The checksum is computed algebraicallyusing integer arithmetic by summing all header and <strong>elevation</strong> bytes containedin the record as 8-bit values. Each byte is considered an unsigned, 8-bitvalue for checksum calculation.3.10.7 DTED on Compact Disc-Read Only Memory (CD-ROM).3.10.7.1 CD-ROM content. The content of the DTED CD-ROM productincludes, in addition to the DTED files, a Digital Mean Elevation Data (DMED)file, and zero or more Gazetteer files. The DMED file provides statisticsabout the <strong>elevation</strong>s in each 15' x 15' area of each DTED cell. The Gazetteersprovide the geographic coordinates for places, cities and other importantlandmark features. In addition, there are four text files that providehelpful information pertaining to the <strong>data</strong> on the DTED CD-ROM. Additionalinformation concerning CD-ROMs can be found in the DoD Military Handbooktitled, MIL-HDBK-9660 DoD-Produced CD-ROM Products.3.10.7.2 Directories. Each DTED CD-ROM contains several hundred DTEDcells, a gazetteer, a DMED file, a text file describing the disc contentsincluding a user’s guide, and a text file describing an Operational NavigationChart (ONC) directory to access the DTED (see Table IV). A series ofdirectories point to the above listed files resident on the CD-ROM. At thehighest level, there are three directories (DTED, GAZETTE, and TEXT) and onefile (DMED). Only the DTED directory contains sub-directories. Within theDTED directory, there is a sub-directory for each longitude containing cells.The sub-directory name format is: DDD, where DDD is degrees. Forexample, the sub-directory name for DTED files contained between the meridians127E and 128E would be : E127. The DTED cell file-name format is:DD.dtX, where DD is degrees and X is the DTED <strong>data</strong> level. For example,the file-name format for a DTED Level 1 cell whose southwest corner is 38N and127E would be: N38.dt1, or starting from the root directory,\DTED\E127\N38.dt1. FIGURE 1 is a Warnier diagram depicting the logical filestructure for a DTED Level 1 cell(page 40).3.10.7.3 CD ROM labeling and packaging. CD ROM labeling, and labelingon the cardboard sleeve, or jewel case liner/information booklet, asapplicable, shall be in accordance with NIMA PI 813-102, Guidelines forLabeling The National Imagery and Mapping Agency's CD-ROMs, and Printing andFinishing of Jewel Case Liners/ Cardboard Sleeves, and Information Booklets.Method of packaging (cardboard sleeves or jewel case) shall be specified inthe contract (see 5.1).3.10.7.3.1 CD labeling. Labeling of DTED CDs shall be in accordancewith standard elements identified in the reference figures in NIMA Instruction8955.1.12
MIL-PRF-89020BTable IV.File Structure Diagram - DTED Level 0 Example3.10.7.4 DTED files. A DTED cell is a single file containing thefollowing information. The CD-ROM is logically formatted/labeled according toISO 9660.3.10.7.4.1 DTED Level 1.Record starts at bytea. User Header Label (UHL: 80 bytes) 1b. Data Set Identification Record (DSI: 648 bytes) 81c. Accuracy Record (ACC: 2700 bytes) 729d. Data Records (Each <strong>data</strong> record is 2414 bytes)* 342958438257etc3.10.7.4.2 DTED Level 2.Record starts at bytea. User Header Label (UHL: 80 bytes) 1b. Data Set Identification Record (DSI: 648 bytes) 81c. Accuracy Record (ACC: 2700 bytes) 729d. Data Records (Each <strong>data</strong> record is 7214 bytes)* 34291064317857etc* The number of records is a function of the DTED level and latitude. A countof 1201 is for a DTED Level 1 cell and a count of 3601 is for a DTED Level 2cell between latitudes 50°S and 50°N. Elevations are two-byte integers, high13
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