On Mon, Mar 31, 2008 at 4:02 PM, Robert Vollmert <[EMAIL PROTECTED]> wrote: > > On Mar 31, 2008, at 12:00, Andy Robinson (blackadder) wrote: > > Also as a civil engineer I can see some merit in having elevation > > data for > > physical objects in the database. However, we don't really have a > > good way > > of collecting data that is remotely accurate to the level at which > > it would > > be significantly useful. Non survey grade GPS just doesn't cut > > muster for > > height data so we should never rely upon that. Even the Ordnance > > Survey > > doesn't currently record height data from survey grade GPS. > > Not sure how common they are, but there's some GPS units with built-in > barometer (Garmin Etrex Vista HCX at least). The data they provide > should be good enough to be useful. > > Cheers > Robert Is the problem with non survey grade GPS that they are just inaccurate, or are they somehow biased? Are we talking about 1 meter, 10 meters or a 100 meters inaccuracy? Perhaps the average of of lot of measurements at the same spot is more reliable?
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