Fundamentals of Surveying (FS) Practice Exam

If the ellipsoidal elevation of a point is 592.8 ft and the geoid separation is -139.4 ft, what is the orthometric height above the geoid?

1. 732 ft

2. 592.8 ft

3. 453.4 ft

4. 732.2 ft

The correct answer is: 732 ft

To determine the orthometric height above the geoid, you need to understand the relationship between ellipsoidal elevation, geoid separation, and orthometric height. The orthometric height (H) can be calculated using the formula: H = Ellipsoidal Height (h) - Geoid Separation (N) In this case, the ellipsoidal elevation of the point is 592.8 ft and the geoid separation is -139.4 ft. Applying the values: H = 592.8 ft - (-139.4 ft) Since subtracting a negative is the same as adding, this becomes: H = 592.8 ft + 139.4 ft H = 732.2 ft Therefore, the orthometric height above the geoid is 732.2 ft, which matches the closest option provided in the choices. The reason this calculation is correct stems from the proper understanding of how the ellipsoidal height and geoid separation interact. By strategically using the negative sign of geoid separation logically, you arrive at the correct orthometric height measurement. The other choices do not account for the necessary adjustment of the negative geoid separation, leading to values that do not represent the correct orthometric height.