1. Lesson 2: Terrestrial Coordinate System and Nautical Charts

2. Lesson 2: Terrestrial Coordinate System and Nautical Charts
AGENDA:
Terrestrial Coordinate System (Lat/Long)
Chart Projections
Chart Interpretation/Scale

3. Applicable Reading:
Hobbs, Chapter 4

4. Earth: A “not-so-perfect” Sphere
Shape and Size of the Earth - “a not-so-perfect sphere”
The Earth is an oblate spheroid (a close approximation to a sphere), but for navigational purposes, it is considered a “true” sphere with a circumference of 21,600 nm.
Equatorial diameter = 6,888 nm
Polar diameter = 6,865 nm (or 23 nm less)
If the earth were represented by a 12 in globe it would be depressed .04 inches or .10 centimeters.
Terrestrial Coordinate System
In order to make measurements on the sphere’s surface, we must develop a system of reference points.
When rotation is introduced, two reference points are defined- the points at which the spin axis pierces the surface of the sphere. On the Earth, these points are called the north and south poles.

5. GEOGRAPHIC COORDINATE SYSTEM
LATITUDE
The world’s Geographic Coordinate system is split into a grid.
LONGITUDE

6. MEASUREMENT OF ARC PRONOUNCED SYMBOL Degrees (°) Minutes (´)
Positions in relationship to Earth’s Coordinates system are expressed in:
PRONOUNCED SYMBOL
Degrees (°)
Minutes (´)
Seconds (´´)

7. LATITUDE PARALLELS 90 °N 80 °N 60 °N 40 °N 20 °N 0 ° Equator 20 °S
Latitude - Any small circle perpendicular to the earth’s axis formed by passing a plane parallel to the plane of the equator.
Latitude is measured along a meridian. The length of one degree of latitude is the same everywhere on earth (60 nm). One minute of latitude is 1nm (or 2000 yds). By convention, latitude is expressed using two digits (08, 39, 89).
40 °S
60 °S
90 °S

8. Longitudinal Parallels
Longitude:
0-180 West
Longitude:
0-180 East
Prime Meridian
(Greenwich England)
0° Longitude
Longitude - The angular distance between the Greenwich meridian and the meridian of a particular point on the earth’s surface. Longitude is measured in degrees of arc from 0 to 180 degrees.
If a point lies between 0 and 180 degrees east of the Greenwich meridian, it is described as having eastern longitude.
Once you get to 180 degrees E then starts at 180 W to 0 (Greenwich meridian.)
Always spoken and written with 3 digits, 020 degrees W.

9. Terrestrial Coordinate System
A Great Circle is defined as a line on the surface of sphere, formed by the intersection of a plane passing through it’s center.
Great circle - The intersection of a plane passing through two points on the surface of the earth and the center of the earth.
The resulting circle is the largest circle that can be drawn on the surface of the earth.
The resulting line on the surface of the earth represents the shortest distance between the two points.
Basically; it splits the Earth in half through the center.
Demonstrate an Orange or Apple by cutting it in half, or just any great circle demonstration.
Meridian - Any great circle formed by passing a plane through the center of the earth at right angles to the equator

10. Equator
The great circle formed by passing a plane perpendicular to the earth’s axis halfway between its poles.
The equator divides the earth into northern and southern hemispheres
One of the two great circles from which all locations on the earth’s surface are referenced.
Equator -

11. Prime Meridian
The meridian that passes through the original position of the Royal Greenwich Observatory near London, England.
Constitutes the second reference line for the terrestrial coordinate system.
All other meridians are referenced to the prime meridian; it divides the earth into the eastern and western hemispheres.
Meridian - Any great circle formed by passing a plane through the center of the earth at right angles to the equator

12. Terrestrial Coordinate System
A Small Circle is any other circle formed on the surface of a sphere by the intersection of a plane not passing through the sphere’s center.
Small circle - Any circle not passing through the center of a sphere .
Parallels (of latitude) - Any small circle on the earth’s surface that is perpendicular to the plane of the equator.

13. Chart Production
Two government agencies are mainly responsible for producing nautical charts - the National Geospatial Information Agency and the National Ocean Service.
National Geospatial Information Agency (NGA) - concerned mainly with the production and upkeep of charts and related navigational publications covering all ocean areas of the world outside U.S. territorial waters.
NOAA/National Ocean Service - concerned with charts covering inland and coastal waters of the United States and its possessions.
Two government activities are mainly responsible for producing nautical charts - the National Imagery and Mapping Agency and the National Ocean Service.
NGA was known as National Imagery and Mapping Agency (NIMA): is concerned mainly with the production and upkeep of charts and related navigational publications covering all ocean areas of the world outside U.S. territorial waters.
NOAA/National Ocean Service is concerned with charts covering inland and coastal waters of the United States and its possessions.

14. TERMS AND DEFINITIONS CHART SCALE:
THE RELATIONSHIP BETWEEN TWO MEASUREMENTS. EXPRESSED AS A RATIO.
THE SCALE TO WHICH A CHART IS DRAWN APPEARS DIRECTLY UNDER ITS TITLE.

15. Scale conversion and reference

16. TERMS AND DEFINITIONS
LARGE SCALE CHART COVERS A SMALL AREA AND ARE USED FOR PILOTING AND INSHORE NAVIGATION.

17. TERMS AND DEFINITIONS
SMALL SCALE CHARTS ARE LESS DETAILED THAN LARGE SCALE CHARTS AND COVER A LARGE AREA.

18. Chart Projections Desirable qualities of a chart projection:
Maintain true shape of physical features.
Maintain correct proportions of features relative to one another.
True scale, permitting accurate measurement of distance.
Rhumb lines plot as straight lines.
Great circles plot as straight lines.
As we’ve already discussed, the earth is considered a spheroid or “not-so-perfect” sphere. Which presents a problem: How to represent the round earth on a flat piece of paper.
Just as a rubber ball, it is physically impossible to spread it out flat without some stretching or tearing.
A sphere is “non-developable” - no part of it can be spread flat without significant distortion.
We get around this by projecting the surface features of the terrestrial sphere onto other surfaces that are developable (e.g. cone and cylinder).

19. MERCATOR PROJECTION:
Developed by Gerhardus Mercatorr some 400 years ago.
The Most Common Projection Used In Maritime Navigation.
Point Of Tangency Is The Equator.
Rhumb lines plot as STRAIGHT lines.

20. Mercator Projection CYLINDRICAL
Imagine a light bulb in the center of a globe, with a sheet of paper wrapped around it in the form of a cylinder. Meridians and parallels would be "projected'' onto the cylinder as straight, parallel lines..
The amount of lateral distortion steadily increases with distance from the equator. Consequently, the latitude scale must be expanded to maintain conformality (true shape). The latitude scale is expanded mathematically on all mercator charts.
The mercator projection is the most widely used projection in marine navigation
Its advantages are:
Position, distance, and direction can all be easily determined
True shape of features is maintained for small areas (it is conformal) .
Its disadvantages are:
Distortion of true size of surface features increases with distance from the equator (significance: always measure distance at the nearest lat).
Great circles appear as curved lines.

21. Mercator Projection
© 1998 GeoSystems Global Corporation

22. Advantages/Disadvantages of the Mercator Projection
Position, distance, and direction can all be easily determined
Rhumb lines plot as straight lines
Meridians plot as straight lines
DISADVANTAGES
Distortion of true size of surface features increases with distance from the equator
Great circles, other than a meridian or the equator, appear as curved lines.

23. Gnomonic Projection AZIMUTHAL
A perfectly flat piece of paper (a plane) would touch the globe at a point. This projection is a good choice for maps with circular or square shapes. When the point of tangency is one of the poles, meridians are shown as straight lines radiating from the pole. If parallels are then drawn as equally spaced concentric circles, this projection would be equidistant (scale is true along any line radiating from the center point, in this case the pole).
Gnomonic Projection: Great circle routes (the shortest distance between two points on the globe) appear as straight lines on this Azimuthal
Its advantages are:
Great circles appear as straight lines. Due to this attribute, the gnomonic chart is mainly used to plot the optimum great circle route (shortest path) between two points. These points are then picked off the gnomonic chart and plotted on a mercator chart
Distortion is tolerable within 1,000 miles of the point of tangency.
Its disadvantages are:
Rhumb lines appear as curved lines
Distance and direction cannot be measured directly
It is not conformal (true shapes are not presented).

24. Advantages/Disadvantages of the Gnomonic Projection
Great circles appear as straight lines.
Uused to plot the optimum great circle route (shortest path) between two points
DISADVANTAGES
Distortion of shape and scale increases as the distance from the point of tangency increases.
Distance and direction cannot be measured directly from a gnomonic projection.

25. Chart Projection Summary
Mercator Gnomonic
Parallels: Straight lines Curved (except equator)
Meridians: Straight Straight
Conformal: YES NO
Great Circles: Curved* Straight
Rhumb lines: Straight Curved lines
Applications: Piloting Great-circle
determination
* Except meridians

26. Mercator vs. Gnomonic

27. Measuring Direction
All rhumb lines on a Mercator projection represent true directions.
Measurement of direction on a Mercator chart is accomplished by using a parallel ruler to transfer the direction of a rhumb line to a nearby compass rose.

28. MEASURING DISTANCE Distance of 1 NM 1 Degree = 60 NM (Nautical Miles)
1 Minute =
1 Nautical Mile
DISTANCE ALWAYS MEASURED ON LATITUDE SCALE!

29. TYPES OF CHARTS GENERAL CHARTS: Small Scale Charts
1:150, :600,000
Used for voyage planning.

30. A voyage plan is first placed on a Mercator chart as a straight line
A voyage plan is first placed on a Mercator chart as a straight line. You get lat/long positions from this chart, and transfer this track to a gnomic projection (next slide)

31. An example of what a voyage plan across the Atlantic Ocean on a gnomic projection

32. TYPES OF CHARTS SAILING CHARTS: Small Scale Charts
1:600,000 - SMALLER
Used For Open Ocean Navigation.

33. TYPES OF CHARTS COASTAL CHARTS: Large Scale Charts
1:50, :150,000
For approaching bays and harbors and used for coastal navigation outlying reefs and shoals.

34. TYPES OF CHARTS HARBOR AND APPROACH CHARTS: Large Scales Charts
1:2,400-1:50,000
Used Primarily For Inshore Navigation and for Navigating Large Inland Waterways.

35. CHART NUMBERING SYSTEM
Designed For Use By The U.S. Navy and U.S. Coast Guard.
Built by Defense Mapping Agency (DMA) who has changed it’s name to:
NATIONAL GEOSPATIAL-INFORMATION AGENCY (NGA)

36. Chart Numbering System
All charts produced by NIMA and NOS are assigned a number from one to five digits, according to the scale and area they depict.
# of digits Scale
No scale involved (supporting pub)
: 9,000,001 and smaller
: 2,000,001 to 1 :1,900,000
Miscellaneous and special, non-navigational charts
: 2,000,000 and larger
The chart numbering system also allows the navigator to organize his/her charts into chart portfolios.

37. Ocean Basins of the World

38. ONE DIGIT CHARTS(1-9) Have no Scale Connections.
Comprise The Symbol And Abbreviation For Charts of The United States And Other Nations.

39. TWO AND THREE DIGIT CHARTS
Covers Very Large Areas Such As:
Entire Ocean Basins
Portions of Ocean Basins.
The World’s Water Are Divided Into Nine Ocean Basins.

40. Coastal Regions of the World
Note: The first two digits of a five digit coastal chart identify the coastal region and subregion in which the charted area is located. The last treed digits place the chart in geographic sequence throughout the sub region.

41. FOUR DIGIT CHARTS Covers Numbers From 5000 to 9999
Non-navigational, Special-purpose Charts Such As:
Special World Charts
Plotting Sheets

42. FIVE DIGIT CHARTS (11000-99999) Covers Portions Of Coastlines.
Most Common Type of Charts By Navigators.
Majority of Nautical Charts Found Aboard Ships

43. CHART NUMBERING
The Five Digits Combined Make Up The Alpha-numeric (Words& Numbers) Prefix.
First Two Digits Are The Sub-region.
Third Digit Is The Portfolio Assignment Number.

44. The Navy Has Three Portfolio Assignments A, B, and X.
“A” Portfolio Consist Of:
All Operating Area Charts
Principal Coastal Charts
Harbor And Approach Charts.

45. PORTFOLIO ASSIGNMENT “B” Portfolios Supplement the “A” Portfolio With:
Additional Coastal Charts
Harbor And Approach Charts
For Each Sub-region.

46. PORTFOLIO ASSIGNMENT “X” Portfolio:
Designated Standard Nautical Charts Which Have Not Been Assigned To Either an “A” Or “B” Portfolio.

47. CHART NUMBERING
The Fourth And Fifth Digits Of The Prefix Specify The Type Of Chart:
“CO” - COASTAL CHARTS
“HA” - HARBOR AND APPROACH CHARTS.
“OA” - OPERATING AREA CHART
“WO” - WORLD
“NR” - NAVY RESTRICTED
“GN” - GENERAL
“TR” - TRAINING

48. NATIONAL GEOSPATIAL-INFORMATION AGENCY (NGA)
NGA STOCK NUMBER
Note: The Complete NGA Stock Number Must Be Used When Requisitioning Charts And Publications.

49. CHART 12245 (1) First Digit Of A Five Digit Chart Is The Region.
(12) First And Second Digit Combined Indicate The Sub Region.
(245) Last Three Digits Are Numbered COUNTERCLOCKWISE Around The Continents.

50. Chart Correction System
Chart corrections are disseminated via Notice to Mariners and Local Notice to Mariners.
Notice to Mariners - issued by NGA and contain changes relating to oceanic and coastal areas worldwide.
Local Notice to Mariners - issued by the U.S. Coast Guard districts and contain changes pertaining only to U.S. inland waters.
Navigators are not required to immediately enter changes on every chart.
Corrections are entered on correction cards when received. The navigator’s staff updates the charts when the ship is scheduled to operate in an area covered by the chart portfolio.
Radio Broadcast Warnings are used to quickly promulgate important changes affecting safety of navigation that cannot wait for the printing of the Notice to Mariners (the changes will be reflected in the next Notice to Mariners).
Talk about buoy in Ches bay when coming back to port. It has been moved out a mile. Shooting TLAM’s in the MED and also out of Haifa Israel the sunk fishing boat right outside the harbor….
Are not printed on paper, but are electronic.
At this time, ships MUST maintain paper charts and navigate by them. It is illegal for ships to replace the use of paper charts with electronic charts. They may, however, use them to complement the traditional paper charts.
TURN TO PAGE 51 in text book to look at chart correction card.

51. REVIEW What is a Great Circle? What is a Small Circle?
2 degrees of Latitude is = how many nm?
What is the difference between a Mercator and Gnomic projection?
Distance is always measured on the LATITUDE Scale.