Navigation Theory Flashcards
Viewed from above, what direction does the Earth spin?
Anti-clockwise.
What format of Lat/Long does the military use?
DMM
Degrees, Minutes, Decimal minutes
What is the definition of a nautical mile?
A nautical mile is equal to 1 minute of latitude along any line of longitude.
What is a great circle?
A great circle is a circle on the surface of a sphere whose centre and radius are those of the sphere itself. The shortest distance between any two points on the surface of a sphere is the smaller arc of the great circle joining them.
What is a Rhumb line?
A regular curve that will cut all meridians at the same angle. The advantages include that direction is constant, it is usable for distances <1000nm but it gives a longer track distance than a great circle route for distances >1000nm.
What is 1nm in feet?
6076 ft
What is 1nm in metres?
1852 m
What is Magnetic Variation?
Magnetic variation is the angular difference between true north and magnetic north at any given point on the Earth’s surface.
To convert true track into magnetic direction, local variation must be applied using the rules…
Variation East, Magnetic Least
Variation West, Magnetic Best
What are Isogonals?
Isogonals connect points of equal magnetic variations.
What acronym explains how to change from one bearing to the next?
CDMVT
Cadbury’s Dairy Milk is Very Tasty
Compass bearing becomes the Magnetic bearing with the application of deviation
The magnetic bearing, is separate from the true bearing by variation.
What is a Geoid?
Geoid
Physical model of the Earth and approximates to MSL
Blue- Geoid
Red- Elipsoid
Yellow- Sphere
What is the difference between perspective and non-perspective projections?
Perspective
True, geometric projections, drawing shadoes which are cast by meridians and parallels on a transparent model of Earth onto a plane surface.
Non-perspective
Also known as mathematical perspective.
If the point of tangency is 45° N/S then the apex angle is ?
If the point of tangency is 60° N/S then the apex angle is ?
45° N/S, Apex Angle = 90
60° N/S, Apex Angle = 120
What are the three types of azimuthal projection?
Polar
Equatorial
Oblique
What types of Mercator projections are there?
General - Upright projection, used along areas on the Equator
Plane/Oblique - User for regions along great circles other than the Equator.
Transverse - used for areas along the poles.
What are False Northing and False Easting?
False easting is a linear value applied to the origin of the x coordinates. False northing is a linear value applied to the origin of the y coordinates.
What is MGRS?
Military Grid Reference System
MGRS is a grid reference system designed to be used with the UTM and UPS grids.
For example:
4QFJ12345678
4Q (grid zone designator, GZD)
FJ (the 100,000-meter square identifier)
12345678 (numerical location; easting is 1234 and northing is 5678)
What is WGS84?
WGS 84 is an Earth-centered, Earth-fixed terrestrial reference system and geodetic datum. It is the most commonly used datum in the UK.
What is an example of a global map datum?
WGS 84
What is the definition of Civil Twilight?
Up to 6° - Civil Twilight
The duration of day at which every day tasks are possible without artificial light.
What is the definition of Nautical Twilight?
Nautical Twilight - Up to 12°
Outline shapes are discernible, bright stars are visible to the naked eye.
What is the definition of Astronomical Twilight?
Astronomical Twilight - Up to 18°
Depending on skyglow, all except faintest stars are visible. Synonymous with complete darkeness when sun is more than 18°+ belwo the sensible horizon.
When viewed from the North Pole, in which direction does the Earth spin?
Easterly / anti-clockwise direction
What shape is the Earth?
Oblate spheroid.
What are the Cardinal directions?
North
South
East
West
What are lines of latitude?
Latitude
Run in horizontal lines from the Earth’s equator, denoted in degrees, minutes and seconds and annotated as N or S.
What are lines of longitude?
Longitude
Run in vertical lines from the Earth’s poles, measured in degress East or West of the meridian that runs through Greenwich.
What is a great circle?
A great circle is a circle on the surface of a sphere in which the centre and radius are that of the Earth itself. It is the shortest distance between any two points on the Earth’s surface.
What is a small circle?
Any circle on the surface of the Earth, who’s centre and radius are not that of the Earth is a small circle.
What are meridians?
Meridian
Semi-great circles that join at the Poles.
Every great circle that joins the Poles forms a meridian/anti-meridian.
All aligned North/South.
What are parallels of latitude?
Parallels of latitude
Small circles on the surface of the Earth, planes parallel to the plane of the Equator.
Lie in an East/West direction
GEOREF
15 degree intervals, Lat/Long, Letters up both sides
UPS - Universal polar stereographic
UTM - Universal Transverse Mercator
Numbers across bottom, letters up the side.
What are the two types of map datum?
Global datum
Local datum
How many time zones are there?
More than 24
25
Where is the international date line located?
Passes through the middle of the Pacific Ocean
If you are travelling West does the sun take more or less time to set?
You are chasing the sun, so you receive more light and delay sunset.
When is Local Mean Time (LMT)?
1200 Noon
The difference between a sidereal and an apparent solar day is what?
What is CDMVT or TVMDC?
Compass → (Subtract West Add East Deviation) → Magnetic → (Subtract West Add East Variation) → True
True → (Add West subtract East Variation) → Magnetic → (Add West Subtract East Deviation) → Compass
What lines on a map join areas that possess the same magnetic variation?
Isogonals
What is the Equator?
Equator, the line around the middle of the Earth at 0 degrees latitude its circumference, is 21,600 nautical miles.
What is a conformal projection map?
In cartography, a conformal map projection is one in which every angle between two curves that cross each other on Earth is preserved in the image of the projection.
Conformal projections, bearings are accurate. Distance can create inaccuracies.
What is an Oblique Azimuthal projection?
