CH Geographic Information Systems 3

Question 1

A hydrographic surveyor discovers a systematic offset between GPS positions and legacy chart features. What GIS process corrects this misalignment?

Accepted Answer

Rubber-sheeting or georeferencing transformation

Answer

Rubber-sheeting or affine georeferencing transforms shift, rotate, and scale legacy data to align with accurately positioned reference data, correcting systematic spatial offsets.

Question 2

In GIS metadata standards, which element specifically documents the horizontal positional accuracy of a hydrographic dataset?

Accepted Answer

Positional accuracy report

Answer

The positional accuracy report element in metadata (per ISO 19115 or FGDC standards) quantifies the closeness of spatial coordinates to their true ground positions.

Question 3

Which type of GIS analysis would a hydrographer use to determine all water depths along a vessel's planned transit route?

Accepted Answer

Profile extraction along a linear path through a bathymetric surface

Answer

Profile extraction samples depth values along a linear transect through a bathymetric raster or TIN, yielding a cross-section of water depths along the planned route.

Question 4

What does the term 'datum shift' mean in the context of hydrographic GIS?

Accepted Answer

A coordinate offset that occurs when converting between different geodetic datums

Answer

A datum shift is the positional difference in coordinates that arises when the same point is expressed in two different geodetic datums, requiring transformation parameters to reconcile.

Question 5

In the S-100 framework (successor to S-57), what is the primary architectural improvement for hydrographic GIS?

Accepted Answer

It supports multiple data types including raster, vector, and gridded data through a universal feature model

Answer

S-100 introduces a universal hydrographic data model that accommodates vector, raster, gridded, and point cloud data, enabling a much richer and interoperable suite of hydrographic products.

(CH) Certified Hydrographer Practice Test

(CH) Certified Hydrographer Practice Test

CH Geographic Information Systems 3