Kingdom Geodetic Reference Frame (KSA-GRF17)
The Kingdom of Saudi Arabia Geodetic Reference Frame 2017 (KSA-GRF17) serves as the official sovereign coordinate reference system mandated by the General Authority for Survey and Geospatial Information (GEOSA). Realized through the National Continuous Operating Reference Station (CORS) network (KSA-CORS), KSA-GRF17 aligns with the International Terrestrial Reference Frame (ITRF2014) at epoch 2017.0 on the GRS80 ellipsoid.
Legacy Transition: Ain el Abd 1970 to ITRF
For decades, legacy surveying in Saudi Arabia—predominantly under Saudi Aramco and early municipal master plans—relied on the Ain el Abd 1970 datum based on the Clarke 1880 ellipsoid. Distortion across the Kingdom can exceed 15-25 meters when compared to satellite-based WGS84/KSA-GRF17. The approved 7-parameter Helmert transformation must be utilized to convert legacy coordinates without distortion.
UTM Projection Zones (36N, 37N, 38N, 39N)
Saudi Arabia spans four Universal Transverse Mercator (UTM) zones from West to East: Zone 36N (Western Borders / Gulf of Aqaba), Zone 37N (Red Sea Coast, Tabuk, Yanbu, Jeddah), Zone 38N (Riyadh, Qassim, Asir), and Zone 39N (Eastern Province, Dammam, Jubail, Arabian Gulf). All central meridians employ a scale factor of k0 = 0.9996 with a 500,000m False Easting.
| UTM Zone | Central Meridian | Coverage in Saudi Arabia | False Easting |
|---|---|---|---|
| Zone 36N | 33°E | Gulf of Aqaba & Western Border | 500,000m |
| Zone 37N | 39°E | Red Sea Coast, Tabuk, Yanbu, Jeddah | 500,000m |
| Zone 38N | 45°E | Riyadh Metropolitan, Qassim, Asir | 500,000m |
| Zone 39N | 51°E | Eastern Province, Jubail, Dammam | 500,000m |
Vertical Datums & KSA-GEOID21 Gravimetric Model
To bridge ellipsoidal heights (h) obtained from GNSS with orthometric heights (H) required for drainage, marine works, and gravity-fed infrastructure, GEOSA released KSA-GEOID21. With an absolute vertical accuracy of ±2.8 cm across mainland Saudi Arabia, it supersedes older global models like EGM2008.
Giga-Project Grid Scale Factor Guidelines
Linear projects (e.g. high-speed rail, NEOM The Line, pipelines) suffer from grid-to-ground distance distortions when using standard UTM projections. For mega-developments, a Low Distortion Projection (LDP) or Local Engineering Grid with scale factor normalized to ground elevation is required.
Official Survey Deliverable Requirements
All engineering surveys submitted to MOMRAH, RCJY, or Giga-Project PMOs must include raw GNSS RINEX logs (minimum 4-hour static occupations on primary stations), network adjustment loop closures (< 1:100,000), and dual coordinate listings in both KSA-GRF17 UTM and local site grid.