Geodetic and Control Surveying
This domain tests whether you can move between the ellipsoid, the geoid, a map projection, and the ground without mixing datums or dropping a scale factor.
Datums and heights
Horizontal coordinates in Oklahoma are commonly referenced to NAD83 (2011) and will migrate to the modernized NATRF2022; vertical coordinates use NAVD88 orthometric heights. GNSS observes ellipsoid height h; orthometric height H = h − N, where N is the geoid separation from a model such as GEOID18. Never mix an ellipsoid height with a NAVD88 elevation in the same adjustment without conversion.
Projections and state plane
Oklahoma has two State Plane zones, North and South, on a Lambert Conformal Conic projection, typically expressed in U.S. survey feet. Grid distance is ground distance multiplied by the combined factor (elevation factor × scale factor). Ground-to-grid is not optional in control work.
Control hierarchy
Passive control (monuments, published coordinates) and active control (CORS, OPUS solutions) each carry error budgets. Traverse and differential leveling remain the checks on GNSS-derived elevations, especially where canopy or multipath is present.
Worked example
A baseline measures 1,000.000 ft on the ground. Elevation factor 0.99995, scale factor 0.99990. Combined factor = 0.99995 × 0.99990 = 0.99985. Grid distance = 1,000.000 × 0.99985 = 999.850 ft. Reporting 1,000.000 as grid would overstate the line by 0.15 ft.
Traps
Applying scale factor without elevation factor; mixing epochs or datum realizations; treating State Plane coordinates as ground coordinates; ignoring convergence when converting azimuths; accepting a single-epoch GNSS vector as final control.