MODULE SEVEN - NAVIGATION MATERIALS

Transcription

1 1 MODULE SEVEN - NAVIGATION MATERIALS CONTENTS Explain the map and how to interpret Marginal Information 2-3 (IO 2I10) [Navigation Pam - paras ] Calculate and plot 4 and 6 figure Grid References 3-4 (IO 2I11) [Navigation Pam - paras ] Explain Relief and Contours 4-5 (IO 2I12) [Navigation Pam - paras ] Explain how to describe Direction and North Points 5-6 (IO 2I13) [Navigation Pam - para ] Demonstrate how to convert bearings 7-8 [Navigation Pam - para ] Demonstrate how to use a Service Protractor 8-9 (IO 2I14) [Navigation Pam - paras ] Demonstrate how to use a Service Compass (Silva) (IO 2I15) [Navigation Pam - paras ] Demonstrate how to Estimate Distance and Compile a Nav Data Sheet (IO 2I17) [Navigation Pam - paras ] Demonstrate how to locate Position (Resections) 13 (IO 2I16) Navigation DO s and DON Ts 14 Illustrations

2 2 Explain the map and how to interpret Marginal Information General 117. Information printed around the edge or margin of the map helps you to work out what the map is showing you. The marginal information may differ slightly in detail and layout from one map to another. On Royal Survey Corps topographic survey maps, a standard layout is generally used and is the one described below. Title Information 118. The title information is shown at the top of the map and consists of: v Type of Map (top left). The type of map section shows the country of which the map represents a small portion, the scale of the map and the type of map (for example: AUSTRALIA 1: TOPOGRAPHIC SURVEY). v Map Title (top centre and bottom right). The title may be the name of an important town or of an area of the map (for example: IMBIL QUEENSLAND). v Reference Box (top right and bottom left). The map series, sheet number and edition number are a unique reference to a map and are shown in the reference box. This information must be used when ordering maps (for example: SERIES R773, SHEET , EDITION 1-AAS). Production Information 119. The production information at the bottom left of the map shows when, by whom and under what authority the map was made. The method of production and an indication of accuracy are also shown. Universal Grid reference 120. Located below the production information in a box which details the method of giving a universal grid reference. As any six figure grid reference is repeated every 100 km, this method is used to make the reference unique. North Point Diagram 121. Located to the right of the universal grid reference is a diagram showing the direction of true, grid and magnetic north for a particular year. The annual change in magnetic north is also given. This diagram may not be to scale so it should not be used to try and gauge or measure correct angles. Scale and Contour Information 122. The scale is located at the bottom centre of the map and consists of both representative fraction and graphic scale. Below the scale is information on the type of map projection and on the contour interval. Legend 123. Below the scale is the legend which contains the colours and symbols which make the detail on a map easy to read. These symbols are called conventional signs and are purely representative. Care should be taken when referring to these symbols because they are not drawn to scale (for example: buildings and the width of roads). 123a. Standard colours used on the map are: 2

3 3 v orange/brown v blue v green v red/brown v black v purple landforms (contours and sand); water (rivers, lakes and swamps); vegetation (orchards and mangrove swamps); roads and built up areas; artificial features (railways and buildings); and overprints (tactical or aeronautical information). Calculate and plot 4 and 6 figure Grid References The Grid Reference System 202. The grid shown on the map is made up of two sets of equally spaced parallel lines intersecting at right angles to form squares. Maps are normally printed with north at the top of the sheet and with the superimposed grid lines running vertically and horizontally. The interval between the grid lines is the same throughout the map and is usually chosen to match the map scale. The intervals shown on military maps are as follows: Scale Interval 1: to 1: m 1 km 1: to 1: m 10 km 1: m 100 km 203. When giving grid references the grid lines are referred to as follows: v Eastings: the vertical grid lines which divide the map from west to east are known as EASTINGS. They are numbered from west to east. v Northings: the horizontal grid lines which divide the map from south to north are known as NORTHINGS. They are numbered from south to north. Giving Grid References 204. When giving grid references the easting (that is the left to right reading of grid values) is always given before the northing (that is the bottom to top reading of grid values). Remember EASTING BEFORE NORTHING. Four Figure Grid references 205. Four figure grid references indicate the position of one grid square only and are useful when identifying major features etc. To indicate a particular grid square the EASTING, (which forms the left or westerly boundary of that square) is selected first. Next the NORTHING, (which forms the bottom or southern boundary of the square), is selected. The two figures for the EASTING and the two figures for the NORTHING, combined in that order, give the four figure grid reference required For example, to work out the four figure gird reference for the square marked "A" in Figure 1 (see page 15): v Select the easting, which forms the western boundary of square marked "A". In this case it is easting 60. 3

4 4 v Select the northing, which forms the southern boundary of square marked "A". In this case it is northing 90. v Thus, the four-figure grid reference for the square marked "A" is GR6090. Six Figure Grid References 207. Six figure grid references indicate positions to within 100 m accuracy. To give a particular grid reference imagine that each side of the square is divided into 10 equal parts (this will mean that the whole grid square would be divided into 100 smaller squares). Example You are asked for a 6 figure grid reference of the point marked "A" in Figure 2, (see page 15). Imagine each side of the Grid Square divided up into ten parts. The house "A" is in the small square 71.7 east and 13.7 north, (ie: easting 71.7 and northing 13.7). Deleting the decimal points the six-figure grid reference to point marked "A" is therefore Grid references are always prefixed with the letters "GR" to avoid confusion. Thus the grid reference would be shown as GR ). Eight Figure Grid Reference 208. Eight figure grid references can normally only be given on maps with a scale of 1: or larger. The method is similar to the six-figure method explained above, except that each small square is again divided into 10 still smaller squares to give accuracy to within 10 m. The result is that the eastings and northings are calculated to four places, and the result is an eight-figure grid reference. For example in Figure 2, the point marked "A" is at GR Explain Relief and Contours Importance of relief 401. The detail of artificial features such as towns, roads and railways changes quite rapidly while the shape of the ground, (hills and valleys etc) changes slowly. The shape or relief of the ground determines the types of things or uses it is put to, where buildings and roads are placed and the location and direction of communications systems. Until you are able to read relief on a map, you will only be able to learn very basic things about the country you are moving through from the map The importance of relief is obvious in navigation and tactics. Relief affects the movement and deployment of units by limiting the routes, along which they may travel, their speed of movement, and the ease or difficulty of attacking or defending an area. Also affected are observation, fields of fire, cover, concealment and the selection of key terrain features. Description of Contours 403. Contour lines are lines on a map connecting points of equal height. They are coloured orange/brown on most maps. The vertical distance between adjacent contour lines is known as the contour interval. The contour interval is shown in the 4

5 5 marginal information (usually above the scale at the bottom of the map). Every fifth contour line is usually shown with a heavier line to help you when measuring height. These heavier lines are called "index contour lines". Contours are marked with their height at convenient places, with their value read correctly when facing up the slope Contours not only give a representation of height but also indicate the shape of the ground. This is best illustrated by Figure 3, which shows the perspective, section and plan of a hill. Contour Patterns 405. Each topographical feature such as a hill, spur or a knoll has it's own particular contour pattern. The most important things to remember about contour patterns are: v Contours close together show steep slopes -see Figure 4, (page 16). v Contours far apart indicate gentle slopes - see Figure 5, (page 16). v When the spacing of contours decreases (reading from high to low) the slope is convex - see Figure 6, (page 17). v When the spacing of contours increases (reading from high to low), the slope is concave - see Figure 7, (page 17) Remember that unless you know the direction of the slope, you may read the contour pattern incorrectly. For example, at a glance, a spur and a re-entrant have the same pattern, but are clearly totally different features. When there are no contour heights marked close by, and there is no feature, such as a river, to show the direction of the slope, always follow the contours to the same point where their height is marked so that you can tell which way the ground falls Reserved. Spot Elevations 411. Spot elevations are points on a map with the height of the particular feature shown alongside, (often the tops of hills etc). This gives accurate information when used in conjunction with contours. Other types of spot elevations are horizontal control points, trig points and benchmarks. Explain how to describe Direction and North Points 501. An observer sees the horizon as a circle with himself or herself at the centre. The observer normally describes the direction of any object by saying that it is north, east, south, west, northeast, north-north-east etc. When navigating, you need to use a more accurate method of describing direction. Two commonly used methods are the degree system, and the mil system. In this module, we will only cover the mils system. The Mils System 505. In the mil system the circle is divided into 6400 mils with 0 mils (or 6400 mils) being the north point. East, south and west are at 1600, 3200 and 4800 mils respectively. Accuracy to the nearest 10 mils is normally fine in map reading. 5

6 The Australian Army uses the mil system. Figure 8 (see page 17) shows how direction is described. North points 507. A bearing gives an accurate indication of the direction from one point to another. A bearing is the angle, measured clockwise that a point makes from fixed zero. In actual practice the fixed zero may be one of three north points: True North (TN), Grid North (GN) and Magnetic North (MN) True North 508. TN is the direction of the geographic North Pole from an observer anywhere on the earth's surface. A line, which passes through any point and the North and South poles, is called a meridian. These lines converge towards each other at the poles and consequently are not parallel In map reading there is rarely a practical need for knowing the direction of TN. As the direction of GN is more easily found and is very close to true north anyway, GN is used in preference. Grid North 510. GN is the direction, in which the north-south grid lines point towards the top of the map, (ie: on most maps, GN is at the top of the map) Reserved. Magnetic North, Magnetic Variation and Grid-Magnetic Angle 512. MN is the direction that a compass needle points when affected only by the earth's magnetic field. As the magnetic pole is not the true north pole, there is a variation or difference between TN and MN at any place. The angle made at the observer between TN and MN is called the magnetic variation of that position As GN is used in map reading more often than TN it is more useful to know the size of the angle between GN and MN. This is called the grid-magnetic angle. Its size is shown in the north point diagram, which shows the angle correct for the year that the map was made. An example appears as figure 9, (see page 17). Annual Change in Magnetic North 514. The position of the magnetic pole is not fixed and the annual change is not constant. However, the annual change can be forecast over a number of years. In WA the annual change is added to find the total grid magnetic angle since the date the map was made. For example, if a map was made in 1980 and the grid magnetic angle at that time was 40 mils west, then the grid magnetic angle for 1999, where the annual change is say 1 mil west per year will be 59 mils (ie: 40 mils + 19 mils)]. Figure 9 shows an example of a north point diagram for WA. Converting Bearings 515. Compass bearings (magnetic bearings) must be converted to grid bearings for plotting on a map. On the other hand, grid bearings taken from a map will have to be converted to magnetic bearings before they can be used on a compass. To convert 6

7 7 bearings, you simply add or subtract the grid magnetic angle, (see figures 9A & 9B on page 18) Reserved In WA where the grid-magnetic angle is to the west, (ie: when magnetic north is to the west of grid north), a simple way to remember whether to add or subtract the grid magnetic angle is: v Magnetic to Grid SUBTRACT (MGS - My Goodness Sake) v Grid to Magnetic ADD (GMA - Good Morning Australia) Example 1 Assume the year is You are asked to convert a magnetic bearing of 780 mils into a grid bearing. The map you are using was made in From the north point diagram on the map you are handed, you see that the grid magnetic angle is 30 mils west in 1975 and that the annual change in the grid magnetic angle is 2 mils west every 2 years. To work out the grid bearing follow these steps: 1. Number of years since map was made = = 24 years 2. Total annual change in grid magnetic angle = (24 years 2 years) x 2 mils = 24 mils 3. Total Grid Magnetic Angle = 30 mils + 24 mils = 54 mils (50 mils)* *Because your compass is only accurate to 10 mils, you normally round up or down to the nearest 10 mils. Therefore, a grid magnetic angle of 54 mils is rounded down to 50 mils. 4. Magnetic Bearing - Grid Bearing SUBTRACT GRID MAGNETIC ANGLE 5. Mag bearing = 780 mils. Grid bearing = 780 mils 50 mils = 730 mils Example 2 Assume it is Using a protractor you measure a bearing on the map of 1570 mils. Obviously this is a grid bearing. You are asked to convert it to a magnetic bearing that you can set on your compass. The map you are using this time has a grid magnetic angle of 40 mils west correct for the year the map was made, The Annual change is 4 mils west every 2 years. What is the magnetic bearing? 7

8 8 Example 2 [continued] 1. Number of years since map was made = = 14 years 2. Total annual change in grid magnetic angle = (14 years 2 years) x 4 mils = 28 mils 3. Total Grid Magnetic Angle = 40 mils + 28 mils = 68 mils (70 mils)* *Because your compass is only accurate to 10 mils, you normally round up or down to the nearest 10 mils. Therefore, a grid magnetic angle of 68 mils is rounded up to 70 mils. 4. Grid Bearing To Magnetic Bearing ADD GRID MAGNETIC ANGLE 5. Grid bearing = 1570 mils. Mag bearing = 1570 mils + 70 mils = 1640 mils Demonstrate how to use a Service Protractor The Service Protractor 519. To measure a bearing accurately on a map, you will need to use a protractor. The correct name for the current service protractor is "Protractor, Semi-circular, RAA, Mils, F6" (see Figure 10 on page 19). As its name suggests, the protractor is semicircular in shape and has two scales, both graduated in 10 mils intervals. The protractor reads from 0 to 3200 mils on its outside scale and from 3200 to 6400 (0) mils on its inside scale The protractor has a black thread fixed to the index mark to help you measure and read bearings. The protractor also includes roamers for maps of the following scales: 1: m, 1: yards, 1: m, and 1:50 000m. It also contains an eight figure grid reference roamer for 1 000m maps. Roamers are used to work out grid references. How to Measure Bearings 522. Measuring grid bearings is very easy. Just follow the method set out in the example below. Example To measure the grid bearing from the road junction at "O" to the road junction at "A" in Figure 12, (see page 19): v Using a ruler and a sharp pencil join points "O" and "A". If the distance between the two points is less than 8cm the line should be extended so that it overlaps the scale when the protractor is positioned on the map. v Place the protractor on the map so that the index mark is directly over the road junction at "O", and the north line is pointing to grid north, (ie: the base of the protractor is parallel to the eastings on the map). v The grid bearing can now be read from the outside scale of the protractor where the pencil line meets it. In Figure 12, the grid bearing is 910 mils. 8

9 To measure bearings between 3200 mils and 6400 mils, rotate the protractor through 3200 mils. Use the same method shown in the above example, except that you read the bearing off the inside scale. To remember which scale to use: v Round part of protractor to the right, read outside scale RIGHT - OUT (ie: bearing between mils) v Round part of protractor to the left, read inside scale (ie: bearing between mils) LEFT - IN 524. If you don't have time to draw a pencil line on the map, the bearing can be measured using the black thread attached to the index mark. This method is not as accurate, but it does have the advantage of not marking the map. Plotting Bearings 525. To plot (or draw) a grid bearing on a map use the following method: v Place the protractor over the map and position the index mark directly over the point on the map from which the bearing is to be plotted, so that the north line is pointing to grid north (e.g.: the point "O" in Figure 12, page 19); v Read off the bearing required on the 10 mil scale and mark the map with a pencil; v Draw a thin line through point "O" and the pencil mark. This mark is the required grid bearing. Back Bearings 526. A bearing gives the direction of a line from the point of observation to an object. It shouldn't come as any surprise to learn that a back bearing gives the direction from that object back to the point of observation. Back bearings come in handy when for example one of your new recruits announces that they have lost a water bottle, compass etc, and you have to "back track" to find it. You also need to know about back bearings so you can do a resection. 526a. Look at Figure 11 on page 19. You will see that the difference between the bearing and the back bearing is 3200 mils. Therefore, for any given bearing, add 3200 mils to find the back bearing (if the bearing is less than 3,200 mils), or subtract 3200 mils, (if the bearing is more than 3200 mils). Examples Bearing = 4350 mils Bearing = 800 mils Back Bearing = = 1150 mils Back Bearing = = 4000 mils 9

10 10 Demonstrate how to use a Service Compass (Silva) Description 610. There are many different types of Silva compasses, but they are all basically the same. With the Silva compass you can plot and calculate bearings quickly and accurately on a map without a protractor. This is because the Silva compass has protractor built into its base plate. Figure 13 (see page 20) shows the major parts of the Type 4 Silva compass. Compass Housing 611. The Type 4 Silva compass has a magnetized needle in a liquid filled plastic housing. The north end of the compass is painted red and has a luminous strip (ie a strip, which glows in the dark). The dial of the compass housing is graduated in 50 mil intervals and rotates freely in the base plate (or at least it should if someone hasn't broken it!). The base of the housing has six parallel orienting lines and an orienting arrow for alignment with the compass needle. On either side of the orienting arrow are luminous points used when marching at night. Base Plate 612. On the base plate is a small magnifying lens. Down the centre of the base plate is an important line called the lubber line. The lubber line is the point against which the graduated dial is measured. It also has a direction arrow and a luminous mark. The left edge of the base plate has a scale in millimetres while the right edge is marked in inches. To help you calculate grid references, the base plate also has roamers for maps of the following scales: 1: yards, 1:50 000m, and 1:25 000m. Taking a Grid Bearing 613. Figure 14 (see page 20) shows how to calculate a grid bearing from a map using a Silva compass. In detail, the procedure is as follows: v Step 1. Place the long edge of the base plate along the desired bearing, making sure you swivel the direction arrow points in the direction that you wish to travel (e.g.: along line "AB" in Figure 14); v Step 2. Turn the compass housing so that the orienting lines are parallel with the eastings on the map; v Step 3. Read the grid bearing off the compass's graduated dial (ie: the number, which is indicated by the lubber line). Note: that before marching, the grid bearing must be converted to a magnetic bearing and the compass reset accordingly. 10

11 11 Taking a Magnetic Bearing 614. The procedure for taking a magnetic bearing to an object is as follows: v Step 1: Hold the compass in the position shown in Figure 15 (see page 20) with the direction arrow pointing to the object. v Step 2: Rotate the compass housing until the orienting arrow is directly beneath the north end (ie: red end) of the compass needle. v Step 3: Read the magnetic bearing off the compass's graduated dial (ie: the number indicated by the lubber line). Setting the Compass on a Magnetic Bearing 615. The procedure for setting a compass on a magnetic bearing for marching by day or night is as follows: v Step 1: Rotate the compass housing until the required bearing on the compass's graduated dial is in line with the lubber line. v Step 2: Hold the compass flat in the palm of your hand and turn your body around until the north end of the compass needle (ie: red end) is directly above the orientating arrow. The direction arrow now points along the required magnetic bearing. Individual Compass Error 616. Each compass has its individual variation. That is, it does not point exactly to magnetic north. The compass needle itself may not be quite true with the markings on the graduated dial, and slight variations may be caused in other ways. The total error may be quite small, but it can be significant, especially in a poor quality compass. Therefore, it is important to have your unit's compasses checked regularly. Any known error should be noted on the compass so that when readings are taken, an allowance can be made Reserved Local Magnetic Attraction 619. Local magnetic attraction is due to the presence of iron or iron ore in the area where the compass is being used. The compass is a delicate instrument and quite small quantities of iron can have a surprisingly large effect on its behaviour. For example, a watch, steel framed spectacles or a steel helmet will affect the compass reading. Precautions should be taken to see that all iron or steel objects are at a safe distance before using the compass. Small articles will be safe in a trouser pocket but larger articles should be placed 2 or 3 m away. Listed below are the safe distances from various common objects: v High tension power lines 80 m v Fencing wire 10 m v Tank 75 m } v Field gun 60 m } not common in cadet activities! v Steel helmet 3 m } 11

12 To check for local magnetic attraction, select two points about 100 m apart. Take a bearing from A to B, then move to B and take a bearing back to A. The two bearings should differ by 3200 mils (ie: they should be back bearings). Any variation indicates a magnetic disturbance at either A or B, or perhaps both. Demonstrate how to Estimate Distance & Compile a Nav Data Sheet Estimating distance When planning a navex, you have to work out how far you will travel on each leg. This can be important because for example, thick vegetation may mean that you can't find your position by looking at the ground. When actually navigating, distance can be measured by the number of paces travelled and of course by time elapsed. Pacing Pacing is the most reliable method of measuring distance. Because each person takes a different length of pace, everyone in your platoon must work out the average number of paces they take for 100 metres over different types of ground. To do this, use a tape measure to accurately measure intervals of 100 metres on different ground types. Then have your platoon pace out the distances and record the number of paces they take. With experience, counting and converting paces into metres will give you an accurate gauge of distance covered. However, it is always a good idea to have a check pacer There are various techniques for pacing. Some cadets find it easier to count every time their right foot comes to the ground, (ie: count every second pace), when they are travelling a long distance. If using this method, obviously the total number of paces counted must be doubled before being converted into metres. Whatever method is used, a reliable way of recording the total paces must be used, otherwise the total number of paces will be forgotten if/when the cadet is distracted. Methods include: v the use of a pace or sheep counter; v tying a knot in a piece of string to represent each hundred paces; v transferring a pebble from one pocket to another at each hundred paces When estimating distance from the map, you must make an allowance for the rise and fall of ground. Where the measured distance on a map is 1000 m, it will only be accurate if the ground is flat. If there is a hill included in the 1000 m, it's height will have to be taken into account and the pace count adjusted for climbing it on one side and going down it the other. The additional pace counts required for various gradients are shown in Figure 16, (see page 21). Time Time is a good check on the distance travelled when movement is continuous and does not involve crossing many obstacles. The average cadet carrying basic equipment will walk over flat, open country at a speed of about 5 km/hr. The factors which could reduce this rate of movement are: relief and drainage; vegetation; night time; the cadet's load; extremes of climate (heat/cold); and the cadet's physical fitness. 12

13 The following rates of movement are provided only as a guide for use in Australia: Non-tactical Movement By day over open undulating country 5000 m/hr 5 km/hr By day in close flat country 3000 m/hr 3 km/hr By day in rough country, deep sand/snow 1500 m/hr 1.5 km/hr The navigation data sheet You should always produce a navigation data sheet before setting off on a cross-country move. A nav data sheet helps you to plan your navigation, and records the bearing and distance between bounds. The nav data sheet can be written on any notepaper, but should be readable so that it can be checked and copied by a check navigator. An example is shown in Figure 17, (see page 21) It is impossible to write down all of the information about the "going" and the "relief" of the ground, and a navigational data sheet can never replace a map. Therefore, the information in the navigational data sheet is only to aid the memory. Demonstrate how to locate position - Resections A resection is a way of finding your position on a map if you can t do so by comparing the detail of your map with the features on the ground. The method is as follows: 1. Select 3 prominent, widely spaced features that you can recognize on the map, and on the ground. [2 features can be used to give an approximate position]. 2. Take magnetic bearings to each of these 3 features using your compass. This will give you 3 magnetic bearings. 3. Convert these magnetic bearings to grid bearings. Remember with a westerly magnetic variation - MAG GRID subtract the Grid to Magnetic Angle. 4. Convert these grid bearings to back bearings by adding or subtracting 3200 mils as appropriate. 5. Using a protractor, plot the back bearings from the 3 features onto the map. 6. The lines that you draw will either intersect to locate your position or form a small triangle of error to indicate the area in which you are located. 13

14 14 NAVIGATION DO s AND DONT s DO s DONT s REMARKS Plot course on map and plan detours Check compass and map at regular intervals Locate each bound before setting off for the next Count paces and estimate distance travelled Allow for error when bound point is small eg: track junction Always stay strictly on your bearing Bypass obstacles by using measured bearings If map and ground differ, stop and go back to known bound point Make route on the ground as you go Rely on your sense of direction Estimate your position and proceed on assumptions Rely on instinct to judge how far you have travelled Expect accuracy +/- metres when bounds are long Let scouts drift off course to take an easier route Attempt to guess your way around an obstacle Blame your map and compass and carry on When the final route is decided use Nav Data Sheet Map and compass are always right Bounds should be made easy to recognize In close country, there is a tendency to over-estimate Aim off using an alternative object When trained scouts can maintain direction Use square method or similar Remember: the map & compass are right - you are wrong 14

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