1. HEPOS A look at the Transformation Between the ETRF and the Greek Reference Geodetic System INF -2357 Vaios Balis – Christos Liapakis Geotech Ltd

2. Projects’ identification  Supervising authority: KTIMATOLOGIO SA “… responsible for the design, implementation and operation of the Greek Cadastral”  Projects: –HEPOS-SUPPLY –HEPOS-MEAS  Projects co-financed by the European Union under the operational programme “Information society”

3. HEPOS SUPPLY  “Supply, installation and maintenance of the fully operational and turnkey HEllenic POsitioning System – HEPOS”  Contractor: Trimble Europe B.V.  Sub-contractors –Geotech Ltd  Site Location  Installation  Operation support –OTENET SA  Communication provider

4. HEPOS SUPPLY  Reference stations: 100 (± 5)  Duration of the project: 2 years  Installation : 7 months –Site location –Reference station installation –Control center installation –Communications

5. HEPOS SUPPLY

6.  98 stations  2 networks  11 single RS  ETRF-2005

7. GGRS 87  Greek Geodetic Reference System 1987  Parallel to WGS 84 –Accuracy ~ 1 x 10 -5  Origin offset from WGS –+199.723 m – -74.030 m – -246.018 m  Projection –Transverse Mercator –Central Meridian: 24º –Scale along central Meridian: 0.9996

8. HEPOS MEAS – Scope of the work  “GPS measurements on control points of the Greek National Triangulation Network and calculation of their coordinates in HEPOS reference system (ETRF 2005, epoch 2007.5)”  “Calculation of 7-parameter transformation from HEPOS reference system to GGRS 87 and vice versa”  Contractor: JV Ceotech – Topomet  Duration : 10 months !!!!

9. Points to be measured  How many points per 1:50000 scale map sheet ? 1:50000 scale map sheet ~ 28 km ~ 22 km

10. 1:50000 scale map sheets  How many 1:50000 map sheets ?

11. Total number of points  How many points ? –8 per each map sheet 1:50000 scale –387 1: 50000 scale map sheets –or roughly 2800 points to be measured

12. Specifications –L1/L2 GPS receivers –Occupation time: 1 hour –Logging interval: 15 sec –Elevation mask : 15º –6 satellites tracked : 90% of session time –PDOP < 4 : 75% of session time –1 Primary base station – REF (24 hours logging) –1 Secondary base station – SEC (logging until all 8 points of the map sheet have been measured)

13. GPS measurements

14. Resources  10 survey crews  2 people per survey crew  5800 L1/L2 receivers with ACU  Handheld GPS for Guidance  Cameras for documentation  4 WD for transportation  Daily data transfers to the office  3 months field work  9 months office work

15. Pre-survey office work

16. Some measured points

17. Some non measured points

18. Total measured points 2470 points

19. Measured point documentation

20. TGO projects 128 TGO projects

21. 7 parameter transformation  TTC SW

22. Transformation residuals

23. Transformation accuracy  1:50000 scale map sheets –Horizontal  Mean value = ± 3 cm  Max Value = ± 5 cm –Vertical  Mean value = ± 6 cm  Max Value = ± 8 cm

24. Transformation accuracy  1:100000 scale map sheets –Horizontal  Mean value = ± 6 cm  Max Value = ± 9 cm –Vertical  Mean value = ± 10 cm  Max Value = ± 17 cm

25. 7 parameter transformation (global)  TTC SW

26. Residuals

27. Residuals – North Greece

28. Residuals - Islands

29. Residuals – West Greece

30. Residuals – Central Creece

31. Residuals – North East Greece

32. Shift grid files

34. Geoid

35. Accuracy HEPOS vs GGRS'87 (m) 0,037-0,040-0,031 0,014-0,0500,012 -0,007-0,0490,009 0,017-0,033-0,035 0,028-0,028-0,037 0,022-0,025-0,039 0,017-0,055-0,006 0,010-0,046-0,029 0,017-0,041-0,020

36. Survey controller application

38. Thank you for your attention…

39. Questions