Geodesy and Control Surveys Flashcards

Which formula correctly relates ellipsoidal height (h), orthometric height (H), and geoid undulation (N)?

Answer: h = H + N

The fundamental geodetic relation is h = H + N, meaning ellipsoidal height equals orthometric height plus geoid undulation at that point.

The GRS80 ellipsoid, the basis of NAD83, is primarily defined by:

Answer: Semi-major axis (a) and inverse flattening (1/f)

GRS80 is defined by its semi-major axis (a = 6,378,137 m) and inverse flattening (1/f = 298.257222101), from which all other geometric parameters are derived.

Earth-Centered, Earth-Fixed (ECEF) coordinates represent positions as:

Answer: 3D Cartesian coordinates (X, Y, Z) with origin at Earth's center of mass

ECEF is a 3D Cartesian system whose X, Y, and Z axes originate at Earth's center of mass, with the Z-axis directed toward the North Pole.

GEOID models such as GEOID18 are used to:

Answer: Convert GPS-derived ellipsoidal heights to orthometric (NAVD 88) heights

GEOID18 provides geoid undulation (N) values across the U.S., enabling surveyors to derive NAVD 88 orthometric heights from GPS ellipsoidal heights using H = h − N.

In network adjustment using least squares, the primary objective is to:

Answer: Minimize the sum of the squares of the weighted residuals

Least squares adjustment finds the best estimates of unknown quantities by minimizing the sum of the squares of the weighted residuals of all observations.

The angular difference between a geodetic (true) azimuth and a grid azimuth at a survey station is called:

Answer: Meridian convergence (mapping angle γ)

Meridian convergence (γ) is the angle between geodetic north and grid north at a specific point in a projected coordinate system such as SPCS or UTM.

Orthometric height is defined as the:

Answer: Height above the geoid, measured along the plumb line direction

Orthometric height (H) is the distance from the geoid to the point, measured along the curved plumb line, and represents the standard definition of elevation.