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ATPL Theory - Module 1 > General Navigation - Directions & Coordinates > Flashcards

General Navigation - Directions & Coordinates Flashcards

Directions & Coordinates

1
Q

What are two terms for the shape of the earth? What do they mean?

A

Oblate spheroid
Ellipsoid
The earth is slightly fatter at the equator

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2
Q

What is the Geoid?

A

The shape that the ocean surface would take under the influence of gravitation and the Earth’s rotation alone, if other influences such as wind and tides were absent

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3
Q

What is the history of the Geoid?

A

It has been an important concept for 200 years, but has been defined to high precision only since advances in satellite geodesy

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4
Q

What’s a reference ellipsoid?

A

A mathematically defined surface that approximates the geoid

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5
Q

What are Reference Ellipsoids used for?

A

As a preferred surface on which geodetic network computations are performed

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6
Q

What’s the most common geodetic reference system?

A

World Geodetic System of 1984
WGS 84

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7
Q

How are the poles defined?

A

The extremities of of the axis of the Earth’s rotation

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8
Q

What is the direction of Earth’s rotation?

A

Anti-clockwise from above

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9
Q

What is true north?

A

The direction from any position on earth to the north pole

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10
Q

How might ‘East’ be defined? And West?

A

The direction is which Earth rotates
The opposite

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11
Q

What are Rhumb lines?

A

Lines of constant track

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12
Q

The Rhumb Line Track between two points of the same latitude would follow…
What would be the track?

A

A parallel of latitude
90degT
270degT

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13
Q

What would be the shortest route between two points of the same latitude?
a) The rhumb line
b) A Great Circle Track

A

B

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14
Q

What is another name for parallels of latitude other than the equator?

A

Small circles

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15
Q

What would your track be if tracking along a meridian?

A

000T or 180T

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16
Q

What are lines of longitude called?

A

Meridians

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17
Q

What’s a meridian’s opposite on the other side of the Earth called

A

Anti-meridians

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18
Q

How many parallels of latitude are there?

A

Infinite

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19
Q

Parallels of latitude and meridians of longitude are a…system

A

Position reference

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20
Q

What determines the accuracy of a position reference system which uses latitude and longitude?

A

The size of the units used

21
Q

What are the units used for defining position using lat and long?

A

Degrees (°) and minutes (‘)

22
Q

How are parallels of latitude described?

A

By their angle, measured at the centre of the Earth, above or below the equator

23
Q

What are the maximum possible latitudes?

A

90°N or 90°S

24
Q

How do we calculate changes in latitude?

A

If in the same hemisphere, we subtract the smaller from the larger
If in different hemispheres, we add one to the other

25
Q

How might changes in latitude calculations be performed on a scientific calculator?

A

N 65° 30’ - = 65 DMS 30 DMS - 32 DMS 14 DMS
N 32° 14’

26
Q

How are meridians of longitude described?

A

By their angle away from the Greenwich/Prime meridian

27
Q

Find another way to phrase how meridians of longitude are described

A

Longitude is the angle measured at the polar axis, between the plane of the prime meridian and the local meridian

28
Q

What’s the maximum longitude of a meridian of longitude? What else can this be called?

A

180°
The Greenwich anti-meridian

29
Q

All meridians point towards…
How is this shown?

A

The north pole
With a north arrow at the end of each meridian, identifying north

30
Q

How is made clear that a number is referring to a meridian of longitude?

A

By using three digits and E/W

31
Q

What’s the change of longitude between 178°E and 178°W?
Why?

A

4°
Change of longitude is always expressed in the shortest way around Earth

32
Q

What’s the rule for calculating change in longitude?

A

Add the two given and if the answer is more than 180°, subtract it from 360°
If in the same hemisphere, subtract the smaller from the larger

33
Q

How accurately do modern navigation systems tend to display positions to?

A

One tenth of a minute

34
Q

How might we find the exact opposite position of a spot on Earth?

A

Change the symbol for latitude e.g. N becomes S
Subtract longitude from 180

35
Q

What’s the approximate circumference of Earth in KM?

A

40,000KM

36
Q

What’s the approximate circumference of the Earth in NM?

A

21,600NM

37
Q

How do we calculate radius from circumference?

A

By reverse engineering 2 x pi x r

38
Q

What’s the other name for the equatorial radius?

A

The semi-major axis

39
Q

What is the polar radius in NM? And the equatorial radius? What’s the difference?

A

3429NM
3440NM
11NM

40
Q

What’s the definition of the ratio of ellipticity?

A

A ratio to describe the difference in radius between the polar and equatorial radius

41
Q

How might the ratio of ellipticity be mathematically described?

A

(a-b)/a
a= Equatorial radius
b= Polar radius

42
Q

What’s the ratio of ellipticity for earth, expressed as a ratio and as a decimal?

A

1/298
0.0033

43
Q

What calculation might we use to calculate a semi-major axis from a semi-minor one?

A

x1.0033
Divide for opposite calculation

44
Q

What’s the most commonly used reference model for GPS systems? What ratio of ellipticity does it use?

A

World Geodetic System of 1984
WGS 84
1/298.25

45
Q

How is Geodetic latitude calculated as opposed to geocentric? How might this be known?

A

Draw a line at right angles to the Earth’s surface and extend it to the plane of the equator
The plumb-line on the ellipsoid

46
Q

Where will geocentric and geodetic latitudes be most different?

A

45°N and 45°S

47
Q

What system for latitudes and longitudes is used for the WGS 84 ellipsoid?

A

Geodetic

48
Q

How is geodetic longitude defined?

A

The angular distance between the prime meridian and another meridian passing through a point on the Earth’s surface

49
Q

Why is the value the same for geodetic and geocentric types of longitude?

A

Because the vertex of the angle is the centre of the Earth - the same as for geocentric longitude

ATPL Theory - Module 1 (17 decks)

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