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Re: Irish grid references

I'm working on the process for exporting observation data from iSpot to recording schemes. iSpot locations are stored as lat/long, and I am converting these to easting/northing coordinates using OS's Grid Inquest software, and then taking the resulting coordinates and converting them to standard six-figure grid references.

However, for Ireland the Grid Inquest software offers a choice of using the Irish Grid (IG) or the Irish Transverse Mercator (ITM) systems, and the coordinates that result from each of these systems are slightly different; or rather, the 100km square reference numbers are very different (but easy enough to work out how each system maps to the 100km letter references), while the remaining coordinate numbers are slightly different. For example, the lat/long:
52.60002401/-7.811107635

produces IG coordinates of:
212848/149833 (which translates as S 128 498)

but the ITM coordinates are:
612796/649878 (which translates as S 127 498)

The differences in resulting grid ref are small, but clearly there are differences.

I haven't been able to find any information on when the change from IG to ITM happened/will be happening (is it still work in progress?). Can anyone enlighten me on the implications, and on which of the systems I should be using in order to provide the best grid refs for the Irish records that I'm supplying to those recording schemes that cover both Britain and Ireland? Which system underlies the mapping in Recorder/MapMate/NBN?

Thanks,
Martin

Martin Harvey
Biological Records Centre
CEH Wallingford

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Re: Irish grid references

See http://en.wikipedia.org/wiki/Irish_Transverse_Mercator

The pertinent point I think is "With ITM there is no provision for using myriad letters and truncated coordinates as there is with the Irish Grid. Every coordinate must be given with at least a six digit easting and northing from the false origin."

For the sake of the various recording programs I would expect sticking to Irish Grid would be best?

Charlie Barnes
Information Officer
Greater Lincolnshire Nature Partnership

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Re: Irish grid references

Hello Martin

The NBN Gateway uses Irish Grid. I have just run your lat/long example (assuming its in WGS84 spatial reference system and not OSNI) through the importing tool and it converts it to S128498 not SP127498. The discrepancy is likely to be due to Irish Grid requires a transformation (WGS84 to Ireland 65) where as ITM doesn't do a transformation.

Best wishes

Graham

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Re: Irish grid references

Thanks for that information, looks like I'm best off sticking with the Irish Grid for the moment at least.

Martin

Martin Harvey
Biological Records Centre
CEH Wallingford