Transformations and OSGM02 user guide - Leica Geosystems

More documents

Recommendations

Info

The Ordnance Survey Geoid model: OSGM02Orthometric height (h) in the UK and Ireland can be found by the formula:h = H - NWhere H is the GRS80 ellipsoidal height, and N is the geoid undulation (geoid-ellipsoid separation).Please note: some publications use the notations of h and H the other way round.OSGM02 uses a grid look-up method, with geoid undulation interpolated from a 1 km grid covering the UK and theRepublic of Ireland.Similar to the Ordnance Survey (Great Britain) OSTN02 transformation, the first stage in calculating the geoid undulationis to identify in which grid cell the ETRS89 point lies. To identify the appropriate grid cell and record numbers in theGB data set follow the procedure given earlier in 'Transforming ETRS89 coordinates to OSGB36 National Grid'.To identify the appropriate grid cell and record numbers in the Northern Ireland dataset, use the following formulae:east_index = (integer_part_of (x/1000)) -550north_index = (integer_part_of (y/1000)) -800record_number = east_index + (north_index x 251) +1To identify the appropriate grid cell and record numbers in the Republic of Ireland dataset, use:east_index = (integer_part_of (x/1000)) -400north_index = (integer_part_of (y/1000)) -500record_number = east_index + (north_index x 351) +1For both Irish datasets the ETRS89 eastings (x) and ETRS89 northings (y) must be computed using the GRS80ellipsoid and ITM projection (see appendix B).Having located the correct cell, find the values of the geoid undulations at the four corners of the cell (sg 0, sg 1, sg 2, sg 3)and the offsets of the point (dx, dy) from the bottom left corner of the cell (x 0, y 0) – as shown in figure 1 above (the seand sn values are used to find the OSTN02 eastings and northings shifts).Transformations and OSGM02 user guide chapter 3v2.1 9/2002 © crown copyrightPage 25
The value of the geoid undulation at point x, y is given as follows:N =(1 – t)(1 – u) sg 0+ ( t)(1 – u) sg 1+ ( t) ( u)sg 2+ (1 – t)( u) sg 3Where: t =dx /1 000 and u =dy /1 000The resulting geoid undulation is subtracted from the ellipsoidal height (H) to give orthometric height (h).Transformations and OSGM02 user guide chapter 3v2.1 9/2002 © crown copyrightPage 26
Page 2 and 3: PrefaceThis grid transformation sof
Page 4 and 5: Data copyrightUser guide copyrightT
Page 6 and 7: Appendix A Transforming ETRS89 GPS
Page 8 and 9: Orthometric heights in these system
Page 10 and 11: ETRS89 explainedBenefitsOrdnance Su
Page 12 and 13: Chapter 2Data overviewBasic princip
Page 14 and 15: Where:1 the record number is a sequ
Page 16 and 17: Where:1 the record number is a sequ
Page 18 and 19: 4 the height of the Geoid above the
Page 20 and 21: For example, to find the record for
Page 22 and 23: Shifts for x, y are:se 0= east_shif
Page 24 and 25: The OSi/OSNI polynomial transformat
Page 28 and 29: Chapter 4Quality statementCoverageO
Page 30 and 31: Appendix ATransforming ETRS89 GPS c
Page 32 and 33: The offset values are given by:dx =
Page 34 and 35: Appendix BConverting latitude and l
Page 36 and 37: ⎛ ⎛ 5 2 5 3 ⎞ ⎛2 21 3 ⎞
Page 38 and 39: Appendix CConverting easting and no
Page 40 and 41: Worked example using Airy 1830 elli
Page 42 and 43: Geoid modelA model of the level sur

Transformations and OSGM02 user guide - Leica Geosystems

Create successful ePaper yourself

Delete template?

Save as template?