Grnd-49 Basic Navigation 1 The Earth

The Earth

Assumed to be a perfect sphere. Rotates east

Great Circle

A circle on the surface of a sphere whose centre and radius are those of the sphere itself. The plane of the great circle passes through the centre of the sphere and divides it into two equal parts.

Small circle

a circle on the surface of a sphere not coinciding with with the centre and radius of the sphere.

Meridian

Semi-great circles which join at the poles of the earth.

Parallel of latitude

Small circles on earth whose planes are parallel to the equator.

What are the units of Angular Measurement

Degrees, minutes, and seconds are units of angular measurement, both as angles at the centre of the circle and as length along the circumference. Each degree has 60 equal minutes divided into 60 equal seconds

Latitude

Angular distance between its place and the equator measured along a meridian

Facts about lines of latitude

Known as parallels

Run in an east-west direction

Measure distance north or south from equator

Are parallel to eachother

Cross the prime meridian at right angles

Lie in planes that cross the earth’s axis at right angles

Get shorter towards the poles with only the equator being a great circle

Longitude

Angular distance between a meridian and the prime meridian (Greenwich UK)

Facts about lines of longitude

Known as meridians

Run in a north-south direction

Measure distance east or west of prime meridian

Are furthest apart at the equator and meet at the poles

Cross the equator at right angles

Lie in planes that pass through the earth’s axis

Are equal in length

Are halves of great circles

Recording Lat and Long

Latitude coordinate in degrees and minutes is written first and is followed by longitude

Maps

A map is a small-scale flat surface representation of some portion of the earth’s surface.

The only true undistorted picture of the earth’s surface is to depict it on a globe

Qualities of Ideal Map

Conformality

Constant Scale

Correct Area

Orthomorphism

Rhumb lines as straight lines

Great circles as straight lines

Conformality

The correct representation of angles.

To possess conformality, a map must have: meridians and parallels intersecting at right angles, and scale expansion along the meridian equal to scale expansion along the parallel at any point

Constant scale

The correct scale at all points in all directions. This is impossible because of the basic difficulty of flattening a spherical surface.

Correct area

This can be achieved, but when areas are shown correctly, directions and shapes are distorted. Correct area also sacrifices conformality.

Orthomorphism

Correct shape. To be orthomorphic, a map would have to be conformal and have constant scale.

Rhumb lines as straight lines

Lines on a chart which intersect all meridians at the same angle, so parallels and meridians. To possess this property, a map must have meridians as parallel straight lines and at the same time be conformal. Mercator fulfills both.

Great circles as straight lines

Very desirable, great circle represents the shortest distance between two points.

Map Projections

The method by which the latitudes and longitudes of locations on the surface of a sphere are transferred to a plane (flat surface).

Always involves distortion.

Types of projections used in air navigation

Cylindrical and conic

Cylindrical Projections

Wrap a sheet of paper around the globe in a cylinder and transfer the geographic features onto it. To achieve projection, the graticule would be rectangular, the cylinder tangent to one line on the globe or intersects two lines of the globe.

Mercator Projection

A cylinder of paper around the equator of a globe map and projected the graticule of the earth onto the cylinder.

Large-scale expansion towards the poles

Has straight meridians and parallels that intersect at right angles

scales can be used to measure distances and are only true along equator or at two standard parallels equidistant at the equator.

Used for navigation for maps of equatorial regions.

Transverse Mercator

Rotated 90° so that it is tangential to the globe along a meridian instead of the equator

Any meridian may be the central meridian based on the area being mapped

The meridians and parallels intersect at right angles.

Scale is correct along the central meridian and is expanded elsewhere.

However, scale errors can be considered to be negligible on any one sheet.

Shapes are preserved, but areas are distorted; the degree of distortion increases with distance from the central meridian.

Great circles are approximate straight lines, and rhumb lines are curved concave to the nearer pole.

Adjoining north/south projections fit each other.

Lambert Conformal

is used in the preparation of ICAO (International Civil Aviation Organization) World Aeronautical Charts which are in common use by the Canadian Forces. This projection makes a good topographical or map-reading map for higher levels, where there is less detail but a much greater field of vision. The Lambert conformal is a modified conical projection which uses two standard parallels to reduce scale errors.

Map Scale

the ratio between a given length on the map and the actual distance on the earth

Three methods of showing scale

A statement in words

A representative fraction where one unit on the map is equivalent to a number of units on earth

A graduated line

Large Scale

Up to 1:250 000

Covers small areas in large amount of detail

Low-level navigation and target identification

Medium scale

1:500 000

Covers larger area with reasonable amount of detail

Medium-level navigation

Small Scale

1:1 000 000

Covers largest area with smallest amount of detail

Higher-level navigation

Map Relief

Representation of changes in elevation of the earth’s surface on a flat plane or map

Methods of showing map relief

Contour lines

Layer tinting

Spot heights

Hachures

Shading

Aeronautical Signs and Symbols

Aeronautical maps depict information to aircrew by the use of signs or symbols. The guide on the back or along the border of each map contains a complete explanation of all signs and symbols.