[time-nuts] Positional accuracy of the M12+T

Rex rexa at sonic.net
Thu Jan 4 05:03:49 EST 2007


On Wed, 03 Jan 2007 22:18:58 +0000, "Poul-Henning Kamp"
<phk at phk.freebsd.dk> wrote:

>But for a band closer to the poles, from roughly 66 to 56 latitude,
>where we have no sats in half the plane and only occasionally pick
>up signals across the polar hole in the constellation, the ellipsoide
>actually isn't one, and its axis are not aligned with the coordinates
>we care for.

You say, "the ellipsoide actually isn't one".  I don't understand what
that might mean. Care to elaborate?

Reading some of the other threads, its agreed that GPS height is less
accurate than surface position. I'm curious, as you get far into the
northern or southern latitudes, does the delta in inaccuracy between the
local position vs height differ versus, say the delta of the
measurements at the equator?

To be more specific: Say at the equator, some GPS reciever determines
its lat/lon position within +- 3 meters but height +- 10 meters. If you
move the same receiver to Sweden, I assume the position accuracy gets a
bit worse. Does the height accuracy change by the same relative delta or
a different one.

The math involved in a good guess is way beyond me, so I'll just ask the
question. Not that it really matters, but I suspect this group might
give me a good answer or at least one that will inform in unexpected
ways.

While we are at it, for a decent quality positional GPS receiver, what
fraction worse would be the typical height accuracy vs the position at
some mid latitude like north US or mid Europe?





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