Fundamentals of Surveying (FS) Practice Exam

GPS elevations are referenced to which of the following?

1. mean sea level

2. geoid

3. NAVD88

4. ellipsoid

The correct answer is: ellipsoid

GPS elevations are referenced to an ellipsoid, which is a mathematically defined surface that approximates the shape of the Earth. The ellipsoid provides a consistent frame of reference for positioning data acquired through GPS technology. When GPS calculates elevation, it does so in relation to this ellipsoidal model rather than a physical surface such as mean sea level or the geoid. Using the ellipsoid provides several advantages in GPS technology, including allowing for a more uniform approach to measuring positions across diverse geographical areas. The other options, while relevant in the context of elevation reference systems, do not serve as the primary reference for GPS measurements. They may be used in various conversions and applications but the GPS height is fundamentally tied to the ellipsoidal model.