Transformations and OSGM02 user guide - Leica Geosystems

Inverse transformation (OSGB36 to ETRS89)To compute ETRS89 eastings and northings from OSGB36 coordinates, an iterative procedure is required:Step 1To start the iteration, compute the ETRS89–OSGB36 easting and northing shifts at the OSGB36 point, using theOSGB36 easting and northing and the method described in procedure for transforming coordinates (page 20).Subtract these shifts from the OSGB36 coordinates to obtain the first estimate of the ETRS89 easting and northing.Step 2Use this estimate of the ETRS89 easting and northing to obtain improved values for the easting and northing shifts, andsubtract these from the OSGB36 coordinates to obtain improved values of the ETRS89 easting and northing.Step 3If the difference between the first shift value and second shift value is more than 0.0001 metres in either easting ornorthing, repeat step 2 until this is not the case.Step 4If ETRS89 latitude and longitude coordinates are required, obtain these from the ETRS89 easting and northing by theprocedure described in appendix C.Transformations and OSGM02 user guide chapter 3v2.1 9/2002 © crown copyrightPage 22