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62 lines
2.5 KiB
HTML
62 lines
2.5 KiB
HTML
<html>
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<head>
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<title>DTED -- Military Elevation Data</title>
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</head>
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<body bgcolor="#ffffff">
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<h1>DTED -- Military Elevation Data</h1>
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GDAL supports DTED Levels 0, 1, and 2 elevation data for read access.
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Elevation data is returned as 16 bit signed integer. Appropriate
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projection and georeferencing information is also returned.
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A variety of header fields are returned dataset level metadata.
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<p>
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<h2>Read Issues</h2>
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<h3>Read speed</h3>
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Elevation data in DTED files are organized per columns. This data organization doesn't fit very well
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with some scanline oriented algorithms and can cause slowdowns, especially for DTED Level 2 datasets.
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By defining GDAL_DTED_SINGLE_BLOCK=TRUE, a whole DTED dataset will be considered as a single block. The
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first access to the file will be slow, but further accesses will be much quicker. Only use that option if
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you need to do processing on a whole file.
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<h3>Georeferencing Issues</h3>
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The DTED specification (<a href="http://www.nga.mil/ast/fm/acq/89020B.pdf">MIL-PRF-89020B</a>) states that
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<i>horizontal datum shall be the World Geodetic System (WGS 84)</i>. However, there are still people using old data files
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georeferenced in WGS 72. A header field indicates the horizontal datum code, so we can detect and handle this situation.
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<br>
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<ul>
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<li>If the horizontal datum specified in the DTED file is WGS84, the DTED driver will report WGS 84 as SRS.</li>
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<li>If the horizontal datum specified in the DTED file is WGS72, the DTED driver will report WGS 72 as SRS and issue a warning.</li>
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<li>If the horizontal datum specified in the DTED file is neither WGS84 nor WGS72, the DTED driver will report WGS 84 as SRS and issue a warning.</li>
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</ul>
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<h3>Checksum Issues</h3>
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The default behaviour of the DTED driver is to ignore the checksum while
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reading data from the files. However, you may specify the environment
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variable DTED_VERIFY_CHECKSUM=YES if you want the checksums to be verified.
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In some cases, the checksum written in the DTED file is wrong (the data producer did a wrong job).
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This will be reported as a warning.
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If the checksum written in the DTED file and the checksum computed from the data do not match, an
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error will be issued.
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<h2>Creation Issues</h2>
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The DTED driver does support creating new files, but the input data
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must be exactly formatted as a Level 0, 1 or 2 cell. That is the size,
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and bounds must be appropriate for a cell.<P>
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<h2>See Also:</h2>
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<ul>
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<li> Implemented as <tt>gdal/frmts/dted/dteddataset.cpp</tt>.<p>
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</ul>
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</body>
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</html>
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