Terrestrial navigation charts

1.

Terrestrial Navigation
Charts

2.

Topics covered
- basic knowledge of chart projections
- 'natural scale' of a chart
- requirements of a chart appropriate for
marine navigation
- Mercator chart and the principles of its construction
- properties of the chart and the degree to which
it meets navigational requirements and its limitations
- use of a chart catalogue ( during chart work )

3.

4.

Projection : method of representing a spheroidal surface
on a plane.
There are many ways ; some look quite odd ,but there will
be always some distortion.

5.

A projection could be thought as being created by
wrapping a plane around a sphere, switching a light on
at a certain position in the sphere, and projecting
features form the sphere (earth) onto the plane.

6.

One way of describing a projection is first to project from
the Earth's surface to a developable surface such as a
cylinder and then to unroll the surface into a plane.
a Cylindrical projection
b. Conical projection
c. Zenithal projection

7.

All projections show somehow distortions in
shape ; bearing ; scale ; area
Any distortions ?

8.

The choice of the projection depend on the requirements
of the user.
The mariners’ chart requirements are :
- course line (rhumbline / great circle) is a straight line
- Orthomorphism ( conformity)
- change of scale negligible
This means correct shape ; bearing and distances ( scale)
This cannot be met in one single projection, most times
only shape and bearing at the expense of scale.

9.

Rhumbline ( loxodrome) : an imaginary line on the
surface of a sphere, such as the earth, that intersects all
meridians at the same angle
The path of the ship maintains a constant compass direction

10.

Great circle
The path of the ship maintains NOT
a constant compass direction, except when …

11.

Orthomorphism ( comformity) :
The angle on earth is the same as in the chart.
¶
¶
earth
¶
¶
chart
Is the chart conformal ?

12.

The scale of a chart
( also called natural scale)
is the ratio of a given
distance on the chart to the
actual distance which it
represents on the earth.

13.

What is the relation between the radius of a parallel of
latitude and the equator ?
What is the relation between 1' in latitude and 1' in
longitude ?

14.

cylindrical projection

15.

The Mercator projection is a cylindrical projection.
Mercator projection :
What happens with the minutes of longitude ?
What happens with the minutes of latitude ?
What happens with scale ?
How is the course line (rhumb line / great circle) represented?
Is the chart conformal ?
Does it fulfil the requirements of the mariner ?

16.

L
51°30’N
40°42’N
NY
equator
Durban
74°W
0°
31°E
29°50’S

17.

L
51°30’N
40°42’N
NY
equator
Durban
74°W
0°
31°E
29°50’S

18.

L
51°30’N
40°42’N
NY
equator
rhumblines
Durban
74°W
0°
31°E
29°50’S

19.

example of a mercator chart

20.

Zenithal projection
Pn
1. all great circles
straight lines
2. no conformity
L
NY
Ps
only useful to plot the
shortest track

21.

Gnomonic chart is a zenithal projection
great circle is a straight line

22.

Conical projection
Pn
Ps
eg conical
projection of
Lambert Gauss

23.

Lambert Gauss is a conical projection
properties :
- conformal
- great circles are straight lines
- parallels are circles
- rhumbline not a straight line
used e.g. in air navigation

24.

part of a conical
projection

25.

Transverse Mercator

26.

Universal Transverse Mercator (UTM)

27.

28.

29.

Universele Transversale Mercator (UTM)
Properties :
- rhumbline is not a straight line
- conformal
- scale change is large
Used in Offshore