Transcript Great circle

CHARTS
•Graticule - grid over
the globe made up of
circles
•Parallels of Latitude
•Meridians of Longitude
•Prime Meridian
•International Date Line
Meridians of Longitude
Circles that pass directly through the
North and South poles (true poles)
 Meridians are measured 180 degrees east
and west of the prime meridian
 Prime meridian passes through Greenwich,
England
 International Date Line is
the meridian 180 degrees
opposite the prime meridian

Parallels of Latitude
Circles on the earth surface that lie
parallel to the equator
 The equator is the line of latitude that is
equidistant between the poles.
Small
Circles
 Circles of latitude get smaller
and smaller towards the poles

Equator =
Great Circle
Both Longitude and Latitude are measured in
degrees, minutes, seconds.
(60 minutes in a degree, 60 seconds in a minute)

Longitude 0o to 180o East and
West from prime meridian
Degrees
0
Minutes
’
Seconds ”
Meldrum Bay is at
450 55 ’ 35 ” lat
830 07 ’ 10 ” long
One nautical mile is 6080
feet, a statute mile is 5280
A nautical mile is one minute
of arc along a great circle
6080 feet to 5280 feet
70 to 60
1.15 to 1
1 knot is slighter faster than 1 mph
60 knots = about 70 mph
Questions

What is located at N44˚27’30”W080˚09’30” ?
Collingwood Airport

What is located at N42˚50’10”W081˚33’20” ?
Melbourne Airport

What is the distance from the Equator to the
North Pole?
5400 NM

What is the distance between N42˚00’00”
W081˚33’20” and N43˚50’00”W081˚33’20” ?
110 NM
MEAN TIME
Time between two transits of a meridian is
apparent solar day – varies
 Mean sun travels at assumed constant
speed
 Mean solar day same all year
 360o passes in 24 hours so 24 hr = 360o
1 hr = 15o
1 min = 15’
1 sec = 15”
 Local mean time set to mid-meridian 15o

Great Circles
Great circles are lines drawn directly
around the Earth that will cut it into two
equal halves.
 The cut would take
place directly through
the center of the Earth
 Great circles are the
shortest distances between
two points on the Earth

Great Circle route
ADIS ABABA
LONDON
GREENLAND
CHARTS
VANCOUVER
•Great circle or great
circle route will be a
circle that cuts through
the center of the globe
•Small circles – all
parallels of latitude
except the equator
•All meridians are great
circles
Rhumb Lines
A rhumb line crosses each meridian of
longitude at the same angle.
 Represents the path
of constant heading
between two points.
 Not the shortest
distance.

How do we make a 2-dimensional
map from a 3-dimensional Earth?
Waldseemuller’s Map of 1507
Mercator Projection
Maintains constant distance between
meridians.
 This causes distortion
towards the poles.
 Straight line on this
map is a rhumb line.

Transverse Mercator projection
Similar to mercator, except the mapping cylinder
is rotated 90 degrees.
 This allows the map-maker to center the
projection on a meridian of longitude.
 Good for small maps (VTAs) or for mapping a
long narrow country like Chile
 Map begins to
distort once you
move away from
the central meridian

Lambert Conformal Conic
Projection
Map maker fits a cone over the Earth.
 The points where the cone is touching the
surface of the Earth are called the
standard parallels.
 Map is accurate at the
standard parallels but
distorts as you move away.
 Used for medium scale
maps (majority of aviation
charts)

Lambert Conformal Conic
Projection
Meridians of Longitude curve in towards
the poles.
 Straight lines represent great circles and
therefore do not maintain constant
headings (unless due north-south)

Great Circle/Rhumb Line on
Mercator
Great Circle/Rhumb Line on
Lambert Conformal Conic
VNC 5000
WAC Chart
VTA
Scale
The scale used on a map depends on it’s
use.
 Large scale (WAC charts) displays a large
area, but not a lot of detail
 Small scale (VTA charts) displays a small
area, and lots of detail
 Medium scale (VNC charts) compromise
between area and scale.

Scale
Ratio of chart length to the distance on
the Earth it represents.
 For example 1:500,000 means 1 inch on
the map equals 500,000 inches on the
ground.


*Remember* 1 minute latitude = 1 NM
Magnetic Variation
The magnetic north pole does not coincide
with the true north pole.
 Maps are aligned with true north, however
our magnetic compass aligns with
magnetic north
 The difference between true north and
magnetic north varies depending on your
location and is called magnetic variation.

East Magnetic Variation
Subtract East Variation from true track to
get magnetic track
 Variation East – Magnetic Least

West Magnetic Variation
Add west variation to true track to get
magnetic track
 Variation West – Magnetic Best

Isogonal vs. Agonal

An isogonal line is a line joining points on
the Earth with equal magnetic variation.

An agonal line is a line joining points on
the Earth with zero magnetic variation
MAGNETIC DEVIATION
Magnetic field from airframe, engine, electrical
system.
Compass card shows deviation & correction
MORE
CHART
STUFF
•CYR 511 all listed in CFS
•Military airfield
•Parachute area
•Abandoned airfield
•Isogonic line
•vs Agonic line
AGONIC LINE
CYKZ 1
CYKZ 2
CYKZ 3
OO 1
OO 2
PQ 1
PQ 2
QA 2
YZ TERMINAL