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Can a GPS measure altitude so I can determine slope for running polypipe?

April 26, 2017altitude determine GPS measure polypipe running slope

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Can a GPS measure altitude so I can determine slope for running polypipe?

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GPS heights are based on an ellipsoid (a mathematical representation of the earths shape), while map and ground elevations are based on a vertical datum tied to the geoid (or what is commonly call mean sea level). Basically they are two different systems, although they have a relationship which has been modelled. The main source of error has to do with the arrangement of the satellite configurations during fix 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 +/- 100m. Use these values with caution when navigating. GPS units do not replace basic map and compass skills!