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Elevation not altitude


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Hi guys, is it at all possible to buy a GPS/ altimeter instrument, that will give what height you are above the ground you are flying over, instead of height you are above sea level. I've watched many videos on paramotoring in the USA, and most of their instruments show both, above sea level and actual height above the ground. I've searched every app in the UK, but can't find one that gives the height above the ground. I can't understand why not, if the GPS map you are using has the above sea level information, why not give another reading of the same, with this above sea level subtracted, making it, above ground level. Please help

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GPS height is generally considered not accurate enough for aviation. The following is a quote from Garmin:

GPS heights are based on an ellipsoid (a mathematical representation of the earth's shape), while USGS map elevations are based on a vertical datum tied to the geoid (or what is commonly called mean sea level). Basically, these are two different systems, although they have a relationship that has been modeled.

The main source of error has to do with the arrangement of the satellite configurations during fixed determinations. The earth blocks out satellites needed to get a good quality vertical measurement. Once the vertical datum is taken into account, the accuracy permitted by geometry considerations remains less than that of horizontal positions. It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft. Use these values with caution when navigating.

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15 hours ago, Jimmy said:

 I've searched every app in the UK, but can't find one that gives the height above the ground.

The above points notwithstanding regarding GPS accuracy the app `Flyskyhy` has an option for height above ground (as well as altitude of course), both options can be configured to be viewable on screen simultaneously.

It appears quite accurate - when flying over the sea both altitude and height above ground displays show the same figure but as soon as i head inland the height above ground changes instantly.

Flyskyhy is a great app.

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