FUNDAMENTAL SURVEYING Geodesy and Map Projections 3

Question 1

What is GEOID18 (or GEOID12B) used for?

Accepted Answer

Converting between ellipsoid heights (GPS) and orthometric heights (NAVD88)

Answer

GEOID18 and GEOID12B are NGS geoid models used to convert GPS-derived ellipsoid heights to NAVD88 orthometric elevations using the relationship h = H + N.

Question 2

The semi-major axis of the GRS80 ellipsoid (used for NAD83) is approximately:

Accepted Answer

6,378,137 m

Answer

The GRS80 ellipsoid has a semi-major axis (equatorial radius) of 6,378,137 m.

Question 3

What is the relationship between geographic (geodetic) latitude and geocentric latitude?

Accepted Answer

Geographic latitude is larger than geocentric latitude except at poles and equator

Answer

Due to the Earth's flattening, geodetic (geographic) latitude is greater than geocentric latitude at all points except the equator and poles.

Question 4

An 'equal-area' map projection preserves which property?

Accepted Answer

Areas of regions

Answer

An equal-area (equivalent) projection maintains correct area relationships between mapped regions, though shapes are distorted.

Question 5

What is the 'Helmert transformation' used for in geodesy?

Accepted Answer

Transforming coordinates between two geodetic datums using translation, rotation, and scale parameters

Answer

The Helmert (7-parameter) transformation converts between coordinate systems using three translations, three rotations, and a scale change.

FUNDAMENTAL SURVEYING Practice Test

FUNDAMENTAL SURVEYING Practice Test

FUNDAMENTAL SURVEYING Geodesy and Map Projections 3