![]() Note that the elevation factor is determined from the ellipsoid height, NOT the orthometric (sea level) height. The distance between the ellipsoid and projection surface produces the Grid factor while the distance between the ellipsoid and the surface produces the Elevation factor. To answer your question, there are two factors that distort any projection distance: the distance between the ellipsoid and the projection surface, and the distance from the ellipsoid to the surface. As a result, most of us start of with GPS using State Plane and arrive at the conclusion that this is what GPS operates in. This is probably due to State Plane being the most functional, largely accepted, largely supported and documented projections available to US surveyors. This is a common misconception among surveyors, and one I held in my early understanding of GPS. This is then projected onto an ellipsoid to produce latitude and longitude, which is then projected onto a conic surface (such as a cylinder or a cone for State Plane) by your data collector. ![]() GPS works in ECEF (Earth Centered Earth Fixed).
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