Geodesy & Coordinate Systems Flashcards

A hydrographer is given coordinates in EPSG:4326. What coordinate reference system do these values represent?

Answer: WGS 84 geographic (degrees)

EPSG:4326 is the code for the WGS 84 geographic coordinate reference system using latitude and longitude in decimal degrees.

What is the maximum angular zone width of a single UTM zone?

Answer: 6°

Each of the 60 UTM zones spans exactly 6° of longitude, numbered 1 through 60 starting at 180°W.

When computing the grid azimuth from a geodetic azimuth in UTM, which correction must be applied?

Answer: Meridian convergence (γ)

Meridian convergence γ is the angle between grid north and geodetic (true) north at any point off the central meridian; grid azimuth = geodetic azimuth − γ.

Which reference frame is the closest practical realization of WGS 84 for precise hydrographic work in the US?

Answer: NAD 83 (2011) epoch 2010.0

NAD 83 (2011) at epoch 2010.0 is the current national adjustment, and its agreement with WGS 84 is typically better than 1 m, making it the practical WGS 84 realization for US surveys.

A geodetic baseline measured along the Earth's surface is 10 000 m. What type of line connects the two endpoints with the shortest path on the ellipsoid?

Answer: Geodesic

A geodesic (or geodetic line) is the shortest path between two points on the surface of an ellipsoid, analogous to a great circle on a sphere.

In hydrographic surveys, the combined scale factor applied to reduce a ground distance to grid distance accounts for which two effects?

Answer: Ellipsoidal scale factor and sea-level correction

The combined factor = k₀ × (sea-level factor), where k₀ is the projection scale factor and the sea-level factor accounts for the reduction from mean Earth radius to the projection plane.

What phenomenon causes the geoid to bulge upward (positive N) near large mountain ranges?

Answer: Excess mass of mountains attracting the geoid upward

The excess mass of mountain ranges exerts a gravitational attraction that pulls the geoid surface upward, resulting in positive geoid undulations in those regions.