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

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”

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

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

HEPOS SUPPLY

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

GGRS 87  Greek Geodetic Reference System 1987  Parallel to WGS 84 –Accuracy ~ 1 x  Origin offset from WGS – m – m – m  Projection –Transverse Mercator –Central Meridian: 24º –Scale along central Meridian:

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 )”  “Calculation of 7-parameter transformation from HEPOS reference system to GGRS 87 and vice versa”  Contractor: JV Ceotech – Topomet  Duration : 10 months !!!!

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

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

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

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)

GPS measurements

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

Pre-survey office work

Some measured points

Some non measured points

Total measured points 2470 points

Measured point documentation

TGO projects 128 TGO projects

7 parameter transformation  TTC SW

Transformation residuals

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

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

7 parameter transformation (global)  TTC SW

Residuals

Residuals – North Greece

Residuals - Islands

Residuals – West Greece

Residuals – Central Creece

Residuals – North East Greece

Shift grid files

Geoid

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

Survey controller application

Thank you for your attention…

Questions