Maritime and Marine Marine Navigation and Charting 2 — Questions and Answers
Question 1: What is the minimum number of GPS satellites needed to compute a two-dimensional position fix (latitude and longitude only)?
- 2
- 3 (Correct answer)
- 4
- 5
Correct answer: 3
At least three satellites are required for a 2D position fix (latitude and longitude), while a fourth satellite is needed to also solve for altitude in a 3D fix.
Question 2: What does 'Differential GPS' (DGPS) primarily improve?
- The number of visible satellites in open ocean
- The accuracy of GPS position fixes by applying land-based correction signals (Correct answer)
- GPS reception during heavy rain or fog
- Battery efficiency of handheld GPS receivers
Correct answer: The accuracy of GPS position fixes by applying land-based correction signals
DGPS uses land-based reference stations to broadcast real-time corrections to GPS signals, significantly improving position accuracy, especially in coastal waters.
Question 3: What does the acronym 'ECDIS' stand for?
- Electronic Chart Data and Information Software
- Electronic Chart Display and Information System (Correct answer)
- Enhanced Course Display and Integrated Steering
- Electronic Coastal Data and Integrated Sonar
Correct answer: Electronic Chart Display and Information System
ECDIS stands for Electronic Chart Display and Information System, a computer-based navigation system that integrates vessel GPS position with electronic navigational charts (ENCs).
Question 4: What does 'COG' indicate on a GPS or chart plotter display?
- Course Over Ground (Correct answer)
- Compass On Grid
- Current Outflow Gradient
- Course of Guidance
Correct answer: Course Over Ground
COG (Course Over Ground) is the actual direction the vessel is tracking over the earth's surface, incorporating the effects of current, leeway, and wind on the vessel's movement.
Question 5: When using a GPS chart plotter near hazards, what is the most critical consideration to avoid position errors?
- Setting display brightness for best visibility
- Verifying the GPS datum matches the chart datum (Correct answer)
- Increasing the chart update rate for smoother movement
- Keeping the screen free of glare and reflections
Correct answer: Verifying the GPS datum matches the chart datum
A mismatch between the GPS datum and the chart datum can cause significant position errors, potentially placing a vessel dangerously close to shoals or rocks.
Question 6: What is a 'waypoint' in electronic navigation?
- A mandatory vessel reporting location required by the Coast Guard
- A predetermined geographic coordinate used as a reference point in route planning (Correct answer)
- A fixed depth contour line on an electronic chart
- A location where a watch change is scheduled to occur
Correct answer: A predetermined geographic coordinate used as a reference point in route planning
A waypoint is a specific set of coordinates (latitude/longitude) saved in a GPS or chart plotter, used as a destination or reference point when planning and executing a route.
Question 7: What does 'SOG' represent on a marine GPS display?
- Speed Over Ground (Correct answer)
- Signal Output Gain
- Satellite Orbit Geometry
- Standard Operating Guide
Correct answer: Speed Over Ground
SOG (Speed Over Ground) is the actual speed of the vessel relative to the earth's surface, accounting for current effects, as opposed to speed through the water measured by a log.
Maritime and Marine Marine Navigation and Charting 2
What is the minimum number of GPS satellites needed to compute a two-dimensional position fix (latitude and longitude only)?