Originally Posted by
magpienja
SDB73, your correct its is a very basic non aviation hand held GPS solely used in a very basic flexwing microlight.
Nick.
I would be surprised if any GPS other than one designed specifically for surveying, ordnance targeting, or rock climbing were to measure a slant range from the current position directly to a way point.
Unless your GPS allows you to set target elevations for your waypoints, it seems pointless to have it do its navigation calculation from a point in space to another point in space (i.e. a 3d track - probably on a trajectory, as a straight line over a reasonable distance may well actually go under ground).
The basic position derived from the satellites is going to be a declination, 'right ascension' and range (i.e. a spherical coordinate system). Ignoring the range, you map this pretty straight into Lat/Lon on the ellipsoid. Then the standard range and direction formula give Great Circle distance along a sphere, which I imagine is what the cheap GPS use rather than the ellipsoid formula or some more complex logic of a 3d path through a specific frame of reference.
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The simple answer remains, it is virtually certain a 'normal' or 'cheap' GPS will do range and bearing calculations based on the lat/lon and ignore altitude (either yours or the waypoints) - hence not slant range.