Dear Pete

Very many thanks for your reply. It is really helpful. I am contacting Alan
Murphy to see if he can help.

Sorry, I was using OS grid to describe the grid used on the Ordnance Survey map
of Jersey (1981), published by the OS and the States of Jersey 1988 and then
attempting to define it in terms of the zone. It is a fieldwork issue, since
mapping in published paper form uses one projection (ED50/UTM) and mapping in
digital form for GIS uses the JTM. Fieldworkers, especially voluntary ones,
don't often have ready access to GIS and it is for this reason that we need to
look for a decent way forwards, without one person always having to be the
conversion agent!

All the best

Amanda



>>> Pete Bland<petebland@...> 07/10/2008 18:57 >>>
On 3 Oct 2008 at 15:16, Amanda Davey wrote:

> OS grid used for Jersey, Channel Islands (ED50 UTM Zone 30N).

If maps were produced on the ED50 datum and using a UTM grid, that
doesn't fit my idea of an "OS" grid. But I know nothing about the
basis on which maps were formerly produced for the island.

> there is a glitch, because Jersey now use the Jersey
> Transverse Mercator (JTM) grid, so all of the points are incorrect for
> that projection.

Current large scale mapping of Jersey appears to be contracted out to
Digimap Jersey, although copyright is owned by the state. Contact
info here:

http://www.digimap.je/product_list

I couldn't readily see any details of the datum and grid used. If you
can get the technical details of the Jersey Transverse Mercator datum
and grid, you ought to be able to set it up as a custom projection in
whatever GIS software you use (Arcview, Mapinfo etc). I assume that
it isn't currently "built in" to those products.

A very useful piece of inexpensive (UK£30) software which I use a
great deal is GPSU:

http://www.gpsu.co.uk/

This makes easy converting GPS data from one projection and grid
system to another. The latest version (4.96) doesn't mention Jersey
Transverse Mercator, although it does include a large number of
others. However the author, Alan Murphy, is usually quick to respond
to requests for new features, and if he could be supplied with the
required technical information, I am sure he would add the necessary
datum and grid to the list of those which GPSU will handle. You
could, at any rate, ask.

Whatever product you end up using I can't see how you are going to
avoid making a conversion.

Pete B