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Difference between NAD83 and WGS84 projected out

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 jaro
(@jaro)
Posts: 1721
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At the center of the earth, the difference between NAD83 and WGS84 is about 4.3 foot or 1.5 meters more or less, depending on the source.

If you were to draw a line between those two centers and project it out to the surface each way, where would those two points be in general terms (which ocean or country).

I guess another way of asking; Where are the two points that the lat long of WGS84 and NAD83 are the same but the elevation is different. I understand that NAD83 is NOT a world wide coordinates system and has no meaning outside of the US, I'm just looking for a better way of explaining the difference between the two.

Thanks,
James

 
Posted : December 28, 2016 9:02 am
bill93
(@bill93)
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I think there is more to it than the difference of the origins. That difference is fixed.

But the coordinates of WGS84(xxx) are a snapshot of the IGS coordinates which are fitted to stations around the whole earth, and NAD83(xxx) is fitted to stations only in the US, so the difference in lat-lon drifts a couple cm per year as the tectonic plates move.

 
Posted : December 28, 2016 9:08 am
(@paul-in-pa)
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"At the center of the earth, the difference between NAD83 and WGS84 is about 4.3 foot or 1.5 meters more or less, depending on the source."

Allegedly WGS84 is at the center of the Earth and the NAD83 center is closer to the US. That offset does not hold for any other ND83 location than along that offset vector. It is my understanding that NAD83 is fixed by some mythical point on the surface, projected down to the center and moves with the surface, so that offset will change with time.

If that vector were projected from the US into the South Indian Ocean the offset would have the opposite sign and would not have an equal value as the ellipsoids are not similar.

Paul in PA

 
Posted : December 28, 2016 11:59 am