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Find "Missing" Elevations with GPS Visualizer

The problem: Sometimes you have geographic data that consists only of latitudes and longitudes, but you want to know the altitudes as well -- because for example, you want to colorize points by height above sea level, or draw a profile of a track. Here are some common reasons why you might have "flat" or incomplete data:

  • Your GPS device does not log altitude, or you had poor satellite reception when you recorded the track.
  • Your GPS device does log altitude, but it's not very accurate.
  • You drew a track using the drawing tools in Google Earth or a similar application, like GPS Visualizer's Sandbox.
  • You have a KML file that came from Google Maps or Google Earth's "driving directions" feature.
  • You created a route in Google Maps and have the URL of that route.
  • You have an NMEA log file that contains only "GPRMC" sentences, not "GPGGA."

Solution #1: DEM database

GPS Visualizer's map, profile, and conversion programs now have the ability to instantly add elevation data -- from a DEM (digital elevation model) database -- to any type of GPS file. If you just want to draw a profile, or convert a single data file to plain text or GPX while adding elevation, you can use the fast and simple form right here:

Upload a file: 
Or provide a URL: 

Output: 
or
Units: 

Or, look in GPS Visualizer's various input forms for the menu called "Add DEM elevation data," and choose one of the elevation databases (described in the table below). Complete copies of the SRTM and USGS NED databases -- 186 gigabytes of raw data -- are stored on GPS Visualizer's server.

Note that the elevation-adding feature will erase any existing altitude data (for example, from a GPS) that might already be in your file. Sometimes this is desirable; profiles made with Digital Elevation Model (DEM) data are usually "smoother" looking than GPS, and typically contain fewer gaps or suspicious readings. (Speaking of gaps, there are a few in NASA's SRTM data, and that's unavoidable. If GPS Visualizer runs into one of these, it will not overwrite those elevations in your input data.)

USGS: NED The U.S. Geological Survey's National Elevation Dataset covers the United States, Canada, and Mexico. 1 arc-second (~30 meter) horizontal resolution is available in most areas (NED1). For Alaska, 60 meter data is also available (NED2).
NASA: SRTM NASA's Space Shuttle Radar Topography Mission includes 90 meter resolution for the entire world (SRTM3). SRTM3 data normally only goes up to about 60° latitude, but thanks to the efforts of the volunteers at Viewfinder Panoramas, GPS Visualizer has the polar regions covered as well. (In addition, the SRTM1 database contains 30 meter resolution for the United States, but overall the data is not as reliable as NED1.)
ASTER ASTER is a joint venture of NASA and the Japanese Ministry of Economy, Trade, and Industry. ASTER has 30 meter coverage of the entire world, but the download process and the massive size of the database make it impractical to store all of it on GPSVisualizer.com. If you need ASTER data for a specific purpose, send an e-mail to the contact address at the bottom of the page, and it might be possible to install a limited number of ASTER tiles.

Solution #2: Google Maps API

The Google Maps API is able to return elevations for points anywhere in the world; these are the same elevations you'd see in Google Earth. Google's data comes from a variety of sources and is sometimes more accurate than the SRTM and NED databases.

The drawback is that there is a limit on the number of queries that can be performed in a day by each user, so GPS Visualizer cannot ask Google for all of your points. To get around this, GPS Visualizer contains a JavaScript-based Elevation Lookup Utility that has your browser perform the queries. To use this tool, your data must be in simple tabular format (easily accomplished using GPSV's plain-text converter); you must remove any existing elevation data; and you must have your own Google Maps API Key. Further instructions are on the Elevation Lookup Utility page.



Quick single-point DEM database lookup:

Coordinates (lat,lon): FIND ELEVATION



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