LSIT Geodesy and Control Surveys 1 — Questions and Answers
Question 1: The geoid is best described as:
- An equipotential surface of Earth's gravity field approximating mean sea level (Correct answer)
- The mathematical surface defined by the WGS84 ellipsoid
- The physical surface of Earth including terrain features
- A perfect sphere used as the reference for geodetic surveys
Correct answer: An equipotential surface of Earth's gravity field approximating mean sea level
The geoid is an equipotential surface of Earth's gravity field that closely approximates mean sea level globally.
Question 2: The difference between ellipsoidal height (h) and orthometric height (H) is called:
- Meridian convergence
- Scale factor
- Geoid undulation (N) (Correct answer)
- Deflection of the vertical
Correct answer: Geoid undulation (N)
Geoid undulation (N) is the signed vertical distance between the ellipsoid and the geoid at a given point, expressed as h = H + N.
Question 3: NAD 83 is based on which reference ellipsoid?
- Clarke 1866
- WGS84
- Bessel 1841
- GRS80 (Correct answer)
Correct answer: GRS80
NAD83 uses the GRS80 (Geodetic Reference System 1980) ellipsoid, while NAD27 was based on the Clarke 1866 ellipsoid.
Question 4: Which vertical datum is the official vertical datum for the contiguous United States?
- NGVD29
- NAVD 88 (Correct answer)
- WGS84
- GRS80
Correct answer: NAVD 88
NAVD 88 (North American Vertical Datum of 1988) replaced NGVD29 as the official vertical datum for the contiguous United States.
Question 5: A benchmark is best defined as:
- A horizontal control monument established by GPS observations
- A temporary reference point used during construction surveys
- A point with known latitude and longitude for horizontal control
- A permanent marked point with a known elevation referenced to a vertical datum (Correct answer)
Correct answer: A permanent marked point with a known elevation referenced to a vertical datum
A benchmark is a permanent, stable monument with a known elevation referenced to a vertical datum such as NAVD 88.
Question 6: NAD 27 was based on which reference ellipsoid?
- GRS80
- WGS84
- Clarke 1866 (Correct answer)
- International 1924
Correct answer: Clarke 1866
NAD27 used the Clarke 1866 ellipsoid with its origin fixed at Meades Ranch, Kansas.
Question 7: The National Spatial Reference System (NSRS) is maintained by which U.S. agency?
- NGS (National Geodetic Survey) (Correct answer)
- USGS (U.S. Geological Survey)
- BLM (Bureau of Land Management)
- FEMA (Federal Emergency Management Agency)
Correct answer: NGS (National Geodetic Survey)
The NGS, a division of NOAA, is responsible for maintaining the NSRS, which defines the national horizontal and vertical control networks.
LSIT Geodesy and Control Surveys 1
The geoid is best described as: