ASCE ASCE Surveying and Geomatics 2 — Questions and Answers
Question 1: What is the horizontal datum used for most modern US surveying and mapping?
- NAD 83 (North American Datum of 1983) (Correct answer)
- NAD 27 (North American Datum of 1927)
- WGS 84
- NAVD 88
Correct answer: NAD 83 (North American Datum of 1983)
NAD 83 is the current horizontal geodetic datum for the US, based on the GRS 80 ellipsoid and realized through a nationwide network of control points.
Question 2: What is the vertical datum for most modern US elevation measurements?
- NAVD 88 (North American Vertical Datum of 1988) (Correct answer)
- NGVD 29 (National Geodetic Vertical Datum of 1929)
- WGS 84 ellipsoid
- MSL (Mean Sea Level)
Correct answer: NAVD 88 (North American Vertical Datum of 1988)
NAVD 88 is the current official vertical datum for the continental US, established by a minimally constrained adjustment based on tidal gauge data.
Question 3: In photogrammetry, what is the purpose of ground control points (GCPs)?
- To georectify aerial imagery to real-world coordinates (Correct answer)
- To identify natural features in photos
- To calibrate the camera lens distortion
- To determine flight altitude
Correct answer: To georectify aerial imagery to real-world coordinates
GCPs are surveyed points with known coordinates used to transform photogrammetric models from image space to a georeferenced real-world coordinate system.
Question 4: What does LiDAR stand for and what does it measure?
- Light Detection and Ranging; measures distances using laser pulses (Correct answer)
- Linear Infrared Detection and Ranging; measures temperature
- Light Intensity Detection and Recording; measures reflectance
- Land Image Detection and Ranging; measures ground cover
Correct answer: Light Detection and Ranging; measures distances using laser pulses
LiDAR emits laser pulses and measures the time for each pulse to return, calculating distances to create dense three-dimensional point clouds.
Question 5: What is the purpose of a metes and bounds description in a property survey?
- To describe a parcel boundary using distances, bearings, and landmark references (Correct answer)
- To list the acreage and assessed value of a property
- To record easements on a property
- To establish the chain of title for a parcel
Correct answer: To describe a parcel boundary using distances, bearings, and landmark references
A metes and bounds description defines a property boundary as a series of courses (bearing and distance) starting and ending at a defined point of beginning.
Question 6: In surveying, what is the geoid and why is it important for GPS elevations?
- An equipotential surface approximating mean sea level; GPS ellipsoidal heights must be converted to orthometric heights using a geoid model (Correct answer)
- The reference ellipsoid used by GPS satellites
- A mathematical model of the Earth's crust thickness
- The satellite orbit reference plane
Correct answer: An equipotential surface approximating mean sea level; GPS ellipsoidal heights must be converted to orthometric heights using a geoid model
The geoid is an equipotential gravitational surface corresponding to mean sea level; subtracting the geoid undulation from GPS ellipsoidal height gives orthometric (useful engineering) elevation.
ASCE ASCE Surveying and Geomatics 2
What is the horizontal datum used for most modern US surveying and mapping?