The Mandate for a Unified National Spatial Reference
Prior to 2017, infrastructure projects in Saudi Arabia operated on a fractured landscape of legacy spatial references. The most prevalent was the Ain el Abd 1970 datum, referenced to the Clarke 1880 ellipsoid, established predominantly for early petroleum exploration concessions by Saudi Aramco.
While sufficient for localized survey plots, regional distortions across the Arabian Peninsula frequently reached 15 to 25 meters when mapped against modern space-geodetic constellations (GPS, Galileo, BeiDou, and GLONASS).
To resolve this geodetic fragmentation, the General Authority for Survey and Geospatial Information (GEOSA) officially established KSA-GRF17 as the sovereign horizontal coordinate reference frame for all public and private civil developments across the Kingdom.
Realization via the KSA-CORS Network
KSA-GRF17 is realized through a nationwide network of over 450 continuously operating GNSS reference stations (KSA-CORS). Key technical parameters include:
- Reference Ellipsoid: GRS80 (a = 6,378,137.0 m, 1/f = 298.257222101)
- Frame Alignment: International Terrestrial Reference Frame 2014 (ITRF2014)
- Reference Epoch: 2017.0
- Plate Kinematics: Arabian Tectonic Plate motion is modeled through official velocity field grids (vx, vy, vz).
The 7-Parameter Helmert Transformation Protocol
When converting legacy survey archives, engineering CAD files, or historic concession plots from Ain el Abd 1970 to KSA-GRF17, contractors must not use single-point approximations. GEOSA mandates a 7-parameter similarity transformation using official values published in GEOSA Circular 2024/08, ensuring horizontal residual errors remain below 5 mm across metropolitan infrastructure corridors.
Giga-Project Implications: Scale Factor Normalization
In linear giga-projects such as NEOM (The Line) and the Saudi Landbridge Rail, standard UTM projections cause significant ground-to-grid distance distortion. Survey scopes for these mega-developments require either a Low Distortion Projection (LDP) or a local ground-scale grid (k = 1.0000000) centered at mean site elevation.