[time-nuts] Averaging Location for Position Hold

Michael Perrett mkperrett at gmail.com
Wed Sep 14 22:46:08 UTC 2011

I was speaking in terms of the user. The point I was trying to make is that
if the user had a map, chart or simply a set of three dimensional
coordinates created from one datum, then that user had better use the same
datum or position errors will be evident. The Z direction is typically used
by navigators to indicate vertical direction, an example of this is when
using the north, east, down (NED) references in an inertial reference frame.


On Wed, Sep 14, 2011 at 2:59 PM, Magnus Danielson <
magnus at rubidium.dyndns.org> wrote:

> Michael,
> On 14/09/11 17:05, Michael Perrett wrote:
>> The user, mostly military or marine, would choose the datum he/she wanted
>> to
>> use. This would match up the local map with the GPS derived position. The
>> difference could be quite large (hundreds of feet), especially important
>> in
>> the Z (vertical) direction!
> In GPS, the Z axis is not the vertical axis... X, Y and Z is the receivers
> position in meters according to GPS/WGS84 which is then translated into
> long, lat and height.
> Cheers,
> Magnus
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