ArcPad projection of GB Nat Grid

ArcPad projection of GB Nat Grid

Post by Keith Hutcheo » Sat, 13 Jan 2001 19:56:10



Anyone know how I can write a projection file for ArcPad that will let me
plug in my GPS unit and get output coordinates in Great Britain National
Grid position format.  Here is an attempt I tried (using the constants
provided in "A Guide to coordinate Systems in Grat Britian" published by the
Ordnance Survey) but it didn't seem to work for the current projection
coordinates in the GPS postition window.  Any suggestions?

PROJCS["GD_?",GEOGCS["GCS_?",DATUM["D_OSGB_1936",SPHEROID["Airy_1830",637756
3.396,299.3249646]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295
5]],PROJECTION["Great_Britain_National_Grid"],PARAMETER["False_Easting",4000
00],PARAMETER["False_Northing",-100000],PARAMETER["Central_Meridian",2],PARA
METER["Latitude_Of_Origin",49],UNIT["Meter",1.0]]

 
 
 

ArcPad projection of GB Nat Grid

Post by Frank Warmerda » Sat, 13 Jan 2001 23:09:37



> Anyone know how I can write a projection file for ArcPad that will let me
> plug in my GPS unit and get output coordinates in Great Britain National
> Grid position format.  Here is an attempt I tried (using the constants
> provided in "A Guide to coordinate Systems in Grat Britian" published by the
> Ordnance Survey) but it didn't seem to work for the current projection
> coordinates in the GPS postition window.  Any suggestions?

> PROJCS["GD_?",GEOGCS["GCS_?",DATUM["D_OSGB_1936",SPHEROID["Airy_1830",637756
> 3.396,299.3249646]],PRIMEM["Greenwich",0],UNIT["Degree",0.017453292519943295
> 5]],PROJECTION["Great_Britain_National_Grid"],PARAMETER["False_Easting",4000
> 00],PARAMETER["False_Northing",-100000],PARAMETER["Central_Meridian",2],PARA
> METER["Latitude_Of_Origin",49],UNIT["Meter",1.0]]

Keith,

What is arcpad? It appears to be using OGC WKT format for projections
definitions, which is nice!  I have attached a definition that I think might
work.  You might need to change the DATUM code to match hwat you had originally.
It appears the main difference is the selection of projection name, which I
think should be "Transverse_Mercator", since BNG is a particular formulation
of transverse mercator.

Good luck,

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[ bng.txt < 1K ]
PROJCS["OSGB 1936 / British National Grid",GEOGCS["OSGB 1936",DATUM["OSGB_1936",SPHEROID["Airy 1830",6377563.396,299.3249646]],PRIMEM["Greenwich",0],UNIT["DMSH",0.0174532925199433]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",49],PARAMETER["central_meridian",-2],PARAMETER["scale_factor",0.999601272],PARAMETER["false_easting",400000],PARAMETER["false_northing",-100000],UNIT["metre",1]]