Fundamentals of Surveying (FS) Practice Exam

How are geodetic heights obtained with satellite surveys measured?

1. With respect to the geoid

2. In geocentric coordinates

3. In state plane coordinates

4. With respect to the ellipsoid

The correct answer is: With respect to the ellipsoid

Geodetic heights obtained through satellite surveys are measured with respect to the ellipsoid. This reference surface is a mathematically defined, smooth, and regular shape that approximates the geoid, which represents mean sea level. The ellipsoidal height is computed based on satellite-derived positions, where the satellite positioning systems, such as GPS, provide the height above this ellipsoidal surface. The use of the ellipsoid is essential in geodesy for a variety of reasons. It allows for uniform reference points that make calculations and comparisons of heights consistent across different locations and reference frames. The ellipsoid provides a simplified model for calculations in a three-dimensional space making it easier to represent the Earth's shape and size in geodetic computations. In contrast, the geoid represents the physical reality of the Earth's surface where gravity is equal, which can vary due to the Earth's topography and density variations. Geocentric coordinates refer to a three-dimensional coordinate system centered on the Earth's mass but do not specifically relate to height measurements. State plane coordinates pertain to a regional system used in surveying over small areas and are not applicable in this context.