GPS to grid reference

Another approach to showing you why an ISO geo-centroid would be
fundamentally different to an ISO meter, litre etc...

Come back in 50 million years and the meter definition will still work.
It is fundamental, invariant.
Come back in 50 million years and there is absolutely no guarantee that
your ISO geo-centroid will be where you put it, as the things you're
defining it by will have changed and moved themselves. It is not
fundamental.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net [email hidden] http://www.dundee.ac.uk/~pjclinch/

In message <[email hidden]>

Peter Clinch said:

Another approach to showing you why an ISO geo-centroid would be
fundamentally different to an ISO meter, litre etc...

Come back in 50 million years and the meter definition will still work.
It is fundamental, invariant.
Come back in 50 million years and there is absolutely no guarantee that
your ISO geo-centroid will be where you put it, as the things you're
defining it by will have changed and moved themselves. It is not
fundamental.

Pete.

That's surely the important issue. The earth is continually changing
shape, the distribution of mass is continually changing within that
shape. There is no identifiable point on the earth that will remain the
same over time. Also the rotational axis will contually vary because of
those changes in shape and mass. It's not even a gradual process either.
You can get measurable step changes following major earthquakes. A GPS
that gave you one conversion before an earthquake for a particular
earthbound location might give you a different conversion after the
earthquake.

Mike
--
o/ \\ // |\ ,_ o Mike Clark
<\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
"> || _`\<,_ |__\ \> | immunology lecturer, antibody engineer and
` || (_)/ (_) | \corn computer user"