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Subject:   Updated SRTM data now available on USGS seamless server -- "half pixel shift" has been fixed
Name:   Dean Gesch
Date Posted:   Feb 6, 07 - 12:28 PM
Email:   gesch@usgs.gov
Message:   Updated 1-arc-second and 3-arc-second SRTM data are now available on the USGS seamless data distribution system (http://seamless.usgs.gov/). The data have been corrected for a half pixel shift in georeferencing that was inadvertently introduced when the SRTM data were originally loaded into the distribution system.

The georeferencing of the SRTM data on the seamless data distribution system now properly reflects the native format NGA DTED convention in which the integer latitude and longitude lines cross at the center of the pixel. For instance, if an exact 1x1-degree square tile of SRTM data is downloaded from the seamless server, the dimensions of the data will be 3601 rows by 3601 columns for 1-arc-second data (or 1201 rows by 1201 columns for 3-arc-second data) and the integer latitude and longitude lines defining the tile extent will intersect precisely at the center of each of the four corner pixels of the grid. This is the same as you would get if the native DTED format SRTM data were ingested for that tile.
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