ASCE Surveying and Geomatics Flashcards

What is the horizontal datum used for most modern US surveying and mapping?

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.

What is the vertical datum for most modern US elevation measurements?

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.

In photogrammetry, what is the purpose of ground control points (GCPs)?

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.

What does LiDAR stand for and what does it measure?

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.

What is the purpose of a metes and bounds description in a property survey?

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.

In surveying, what is the geoid and why is it important for GPS elevations?

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.