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USGS DEM – The USGS' Digital Elevation Model GTOPO30 – Large complete Earth elevation model at 30 arc seconds, delivered in the USGS DEM format; DTED – National Geospatial-Intelligence Agency (NGA)'s Digital Terrain Elevation Data, the military standard for elevation data; World file – Georeferencing a raster image file (e.g. JPEG, BMP)
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DTED (or Digital Terrain Elevation Data) is a standard of digital datasets which consists of a matrix of terrain elevation values, i.e., a Digital Elevation Model.This standard was originally developed in the 1970s to support aircraft radar simulation and prediction.
Hypsometry (from Ancient Greek ὕψος (húpsos) 'height' and μέτρον (métron) 'measure') [1] [2] is the measurement of the elevation and depth of features of Earth's surface relative to mean sea level. [3] On Earth, the elevations can take on either positive or negative (below sea level) values.
A data set which describes the global average of the Earth's surface curvature is called the mean Earth Ellipsoid. It refers to a theoretical coherence between the geographic latitude and the meridional curvature of the geoid. The latter is close to the mean sea level, and therefore an ideal Earth ellipsoid has the same volume as the geoid.
1913 saw the beginning of the International Map of the World initiative, which set out to map all of Earth's significant land areas at a scale of 1:1 million, on about one thousand sheets, each covering four degrees latitude by six or more degrees longitude. Excluding borders, each sheet was 44 cm high and (depending on latitude) up to 66 cm wide.
GTOPO30 is a digital elevation model for the world, developed by United States Geological Survey (USGS). It has a 30-arc second resolution (approximately 1 km), [1] and is split into 33 tiles stored in the USGS DEM file format. According to DTED and USGS DEM the absolute vertical accuracy of GTOP30 varies from ±30 meters. [2]