![]() Previously, SRTM1 data was only available for the United States (and was not very useful because NED1 is generally better), but now NASA has released SRTM1 tiles for the entire world. NASA's SRTM1 database (from the Space Shuttle Radar Topography Mission) has a resolution of about 30 meters. USGS also produces 1/3-arc-second data (NED13), but because those files are nine times larger than NED1 files, only a few mountainous areas (Cascade Range, Sierra Nevada, southern Utah) are available on GPS Visualizer. For Alaska, 60-meter data is also available (NED2). 1 arc-second (~30-meter) horizontal resolution is available in most areas (NED1). Geological Survey's excellent National Elevation Dataset covers the United States, Canada, and Mexico. If GPS Visualizer runs into one of these, it will not overwrite those elevations in your input data.) DEM data sources NED (USGS) ![]() (Speaking of gaps, there are a few in NASA's SRTM data, and that's unavoidable. Often, this is desirable profiles made with DEM data are usually "smoother" looking than GPS, and typically contain fewer gaps or suspicious readings. Note that the elevation-adding feature will erase any existing altitude data (for example, from a GPS) that might already be in your file. ![]() Complete copies of the SRTM3 and USGS NED databases, as well as a large number of SRTM1 and ASTER tiles, are stored on GPS Visualizer's server - that's more than 250GB of raw data.
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