Changes to Ordnance Survey GNSS control networks and geoid models for Great Britain, Ireland and Northern Ireland
Changes to Ordnance Survey GNSS control networks and geoid models for Great Britain, Ireland and Northern Ireland
The three Ordnance Survey organisations have been working together to improve the OSGM02 geoid model resulting in OSGM15. OSGB has also updated the horizontal transformation OSTN02 to create OSTN15. The horizontal transformation polynomial for Ireland and Northern Ireland is unchanged.
OSGB, OSI and OSNI will all switch to using the new systems on 26th August 2016.
At the same time, all three organisations will switch to using updated coordinates for their GNSS control networks (active stations).
New active station coordinates
OSGB, OSI and OSNI will all implement the active station coordinate change on 26th August.
OS RINEX data downloaded on or after that date will contain the new coordinates in the header, hence some customers may find small inconsistencies in the post processed coordinates of data observed before and after 26th August. RINEX data will not be available with the "old" active station coordinates after that date.
Leica Geosystems will also switch to using the updated station coordinates for the SmartNet real-time services and for the SpiderWeb services: RINEX data service, SmartRINEX data service and Point Computation service. Again, it is not possible for us to provide these services in both old and new coordinates so only the new coordinates will be used going forward.
New geoid models and new horizontal transformation for Britain
In Britain, OSGB has developed OSTN15 and OSGM15. Hence new Leica coordinate system files have been created (still based on the same ellipsoid and projection) for users to load into field kit and office software. The new coordinate system is called OSGB36(15) and can be downloaded from http://www.leica-geosystems.com/common/shared/downloads/inc/downloader.asp?id=27512
In Ireland and Northern Ireland there is no new horizontal transformation, but there are 2 new geoid models relating to Malin Head and Belfast Lough. The new Leica geoid model files have been called OSGM15RoI and OSGM15NI respectively. New coordinate systems have been created and can be downloaded from http://www.leica-geosystems.com/common/shared/downloads/inc/downloader.asp?id=27513
Size of horizontal change
In Britain, the average size of active station coordinate change is below 2cm in both plan and height. In Ireland and Northern Ireland the average coordinate change is slightly less.
In Ireland and Northern Ireland the horizontal transformation has not changed so the resulting grid coordinates will only be affected by updated active station coordinates. In Britain however, grid coordinates could be affected by both the updated active station coordinates and the changes to the transformation model (OSTN15 relative to OSTN02). Typically the effect of the transformation model changes counteract the changes in the active station coordinates. Hence SmartNet users would see an average change in grid coordinates of 11mm between work carried out on 25th August using OSTN02 and work carried out on 26th August using OSTN15. Of course, that's an average value and there will be local variations, but in general any "step" in plan coordinates from work carried out with SmartNet before and after 26th August 2016 will be within RTK GNSS accuracy.
Size of vertical change
The average change in computed orthometric heights from OSGM15 compared to OSGM02 has not been calculated by either OSi or Land and Property Services. In Britain the average change in orthometric heights compared to OSGM02 is 26mm (root mean square change values). However, the map shows that in some areas – particularly in parts of Scotland - the level change is significantly bigger than that. In areas shaded yellow, orange and red you'll get smaller level values from OSGM15 than from OSGM02 therefore the ground will appear to have risen locally. The opposite is true for the blue and purple shaded areas.
More technical detail can be found in the July/August issue of the ICES "Civil Engineering Surveyor" magazine or in the July/August issue of the RICS "Geomatics World" magazine: http://www.pvpubs.com/DigitalEdition/GeomaticsWorld/GW201607/HTML/index.html#18
Please contact Leica Geosystems Technical Support on 01908 513429 regarding any queries around OSTN15.
The three Ordnance Survey organisations have been working together to improve the OSGM02 geoid model resulting in OSGM15. OSGB has also updated the horizontal transformation OSTN02 to create OSTN15. The horizontal transformation polynomial for Ireland and Northern Ireland is unchanged.
OSGB, OSI and OSNI will all switch to using the new systems on 26th August 2016.
At the same time, all three organisations will switch to using updated coordinates for their GNSS control networks (active stations).
New active station coordinates
OSGB, OSI and OSNI will all implement the active station coordinate change on 26th August.
OS RINEX data downloaded on or after that date will contain the new coordinates in the header, hence some customers may find small inconsistencies in the post processed coordinates of data observed before and after 26th August. RINEX data will not be available with the "old" active station coordinates after that date.
Leica Geosystems will also switch to using the updated station coordinates for the SmartNet real-time services and for the SpiderWeb services: RINEX data service, SmartRINEX data service and Point Computation service. Again, it is not possible for us to provide these services in both old and new coordinates so only the new coordinates will be used going forward.
New geoid models and new horizontal transformation for Britain
In Britain, OSGB has developed OSTN15 and OSGM15. Hence new Leica coordinate system files have been created (still based on the same ellipsoid and projection) for users to load into field kit and office software. The new coordinate system is called OSGB36(15) and can be downloaded from http://www.leica-geosystems.com/common/shared/downloads/inc/downloader.asp?id=27512
In Ireland and Northern Ireland there is no new horizontal transformation, but there are 2 new geoid models relating to Malin Head and Belfast Lough. The new Leica geoid model files have been called OSGM15RoI and OSGM15NI respectively. New coordinate systems have been created and can be downloaded from http://www.leica-geosystems.com/common/shared/downloads/inc/downloader.asp?id=27513
Size of horizontal change
In Britain, the average size of active station coordinate change is below 2cm in both plan and height. In Ireland and Northern Ireland the average coordinate change is slightly less.
In Ireland and Northern Ireland the horizontal transformation has not changed so the resulting grid coordinates will only be affected by updated active station coordinates. In Britain however, grid coordinates could be affected by both the updated active station coordinates and the changes to the transformation model (OSTN15 relative to OSTN02). Typically the effect of the transformation model changes counteract the changes in the active station coordinates. Hence SmartNet users would see an average change in grid coordinates of 11mm between work carried out on 25th August using OSTN02 and work carried out on 26th August using OSTN15. Of course, that's an average value and there will be local variations, but in general any "step" in plan coordinates from work carried out with SmartNet before and after 26th August 2016 will be within RTK GNSS accuracy.
Size of vertical change
The average change in computed orthometric heights from OSGM15 compared to OSGM02 has not been calculated by either OSi or Land and Property Services. In Britain the average change in orthometric heights compared to OSGM02 is 26mm (root mean square change values). However, the map shows that in some areas – particularly in parts of Scotland - the level change is significantly bigger than that. In areas shaded yellow, orange and red you'll get smaller level values from OSGM15 than from OSGM02 therefore the ground will appear to have risen locally. The opposite is true for the blue and purple shaded areas.
More technical detail can be found in the July/August issue of the ICES "Civil Engineering Surveyor" magazine or in the July/August issue of the RICS "Geomatics World" magazine: http://www.pvpubs.com/DigitalEdition/GeomaticsWorld/GW201607/HTML/index.html#18
Please contact Leica Geosystems Technical Support on 01908 513429 regarding any queries around OSTN15.
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