LSIT Geodesy and Control Surveys 4

Question 1

Which geoid model is the official vertical datum reference for the conterminous United States?

Accepted Answer

GEOID12B

Answer

GEOID12B is the NGS model used to convert between ellipsoidal heights (GPS) and orthometric heights relative to NAVD 88.

Question 2

A surveyor measures an EDM slope distance of 1,523.47 ft at a zenith angle of 88°14'30". What correction must be applied first before reducing to horizontal?

Accepted Answer

Slope reduction using the zenith angle

Answer

Slope reduction (H = S × sin(zenith angle)) is applied first to obtain the horizontal distance before grid or sea-level corrections.

Question 3

In a geodetic survey, the 'deflection of the vertical' refers to:

Accepted Answer

The angular difference between the normal to the ellipsoid and the direction of gravity

Answer

Deflection of the vertical is the angle between the ellipsoidal normal and the local plumb line (direction of gravity), affecting astronomic vs. geodetic positions.

Question 4

What is the primary purpose of a Helmert transformation in geodesy?

Accepted Answer

Transform coordinates between two different datums using scale, rotation, and translation parameters

Answer

A Helmert (seven-parameter) transformation shifts, rotates, and scales a 3D coordinate set to align it with another datum.

Question 5

When performing a GPS survey to establish vertical control, the orthometric height (H) is derived by:

Accepted Answer

H = h − N

Answer

Orthometric height H equals ellipsoidal height h minus the geoid undulation N (H = h − N).

(LSIT) Land Surveyor in Training Practice Test

(LSIT) Land Surveyor in Training Practice Test

LSIT Geodesy and Control Surveys 4