Re: GPS to grid reference

Bernard Hill wrote:

My horror arose when someone said that there were several versions of latitude and longitude. For instance that the N pole is not 90°N in all systems.

That's horrendous because in my book the N pole is *defined* as 90°N and similarly the equator and S pole.

But that's your book. Why should it be the same as everyone else's, if other people have a slightly different job in mind?

The coordinate systems evolved, just as the metre evolved. They were not designed with the knowledge which we have today... which is why the basic units of measurement were redefined by scientists.

But the same scientists have *not* seen fit to propose an ISO co-ordinate system for planetary co-ordinate systems! The definitions of unit distances are not really the same thing at all as co-ordinate systems, which are a certain way of using measurements, not the measurements themselves.

And to say the lat/long was "defined by scientists" is invidious because you have to ask "what scientists?" and "using what tools?".

The ones given the task of finding a way around a big ocean and getting back to where you came from, using whatever tools they could find or devise. What of it?

Modern tools are radically different. I strongly suspect that NASA know where the centroid of the earth is so that they can calculate the course for their unmanned spacecraft. In the same way as the metre, second, coulomb (etc)
were put on a different footing only last century it's time we agreed on latitude and longitude:

But to what end? As long as we know where we are using whatever datum we are using there is no need to create a "standard" lat/long. The nearest it's been to being agreed is WGS84, but as has been pointed out repeatedly, WGS84 is not all things to all men so there's no point in imposing it on those for whom that is the case. If you like to work in inches rather than meters you can, and it's just a scalar conversion to go to the formally defined measurement unit but it doesn't work anything like that with terrestrial co-ordinate systems, so the comparison to ISO fundamental units is irrelevant. If you have a co-ordinate system forced on you that doesn't work as you need it to you can't just multiply by a constant to make it all right.

indeed I suspect that a system is already there which we can adopt. Star positions are quoted in Right Ascension and Declination - a different way of saying latitude and longitude, and stars are accurately recorded, in fact we measure movement.

They are recorded using a system developed for that specific use. Lat/long was itself developed for a specific use. Standardising it as an ISO fundamental does not make any real sense though.

Pete.
--
Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
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Relevant Pages

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