Geodesy and Map Projections Flashcards
6 cards from real FUNDAMENTAL SURVEYING practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Geodesy and Map Projections flashcards as text
What is GEOID18 (or GEOID12B) used for?
Answer: Converting between ellipsoid heights (GPS) and orthometric heights (NAVD88)
GEOID18 and GEOID12B are NGS geoid models used to convert GPS-derived ellipsoid heights to NAVD88 orthometric elevations using the relationship h = H + N.
The semi-major axis of the GRS80 ellipsoid (used for NAD83) is approximately:
Answer: 6,378,137 m
The GRS80 ellipsoid has a semi-major axis (equatorial radius) of 6,378,137 m.
What is the relationship between geographic (geodetic) latitude and geocentric latitude?
Answer: Geographic latitude is larger than geocentric latitude except at poles and equator
Due to the Earth's flattening, geodetic (geographic) latitude is greater than geocentric latitude at all points except the equator and poles.
An 'equal-area' map projection preserves which property?
Answer: Areas of regions
An equal-area (equivalent) projection maintains correct area relationships between mapped regions, though shapes are distorted.
What is the 'Helmert transformation' used for in geodesy?
Answer: Transforming coordinates between two geodetic datums using translation, rotation, and scale parameters
The Helmert (7-parameter) transformation converts between coordinate systems using three translations, three rotations, and a scale change.
What is the 'deflection of the vertical'?
Answer: The angular difference between the direction of gravity (plumb line) and the normal to the reference ellipsoid
The deflection of the vertical is the angle between the actual gravity vector (geoid normal) and the ellipsoidal normal at a given point.