Azumith and BearingsDetermination of angles and directions

BearingThe purpose of a bearing is to give an accurate indication of direction from one point to another.

Based on the magnetic properties. Free floating magnet indicates NORTH

Simply, a bearing is a horizontal angle measured clockwise from a fixed reference line.

Bearing and DistanceLocate the objects with Bearing and DistancePrinciple of SurveyingABCDEFO

Latitude and LongitudeThe spherical Earth is divided into a grid pattern using north-south lines (longitude) and east-west lines (latitude). The basic east west line is the Equator This is the zero line of latitude. Parallel lines above and below the equator are then drawn in. The poles are 90o north and south of the equator. The basic north-south line is called the Prime Meridian, it is the zero line of longitude. It is drawn from the geographic north pole to the geographic south pole through Greenwich, England.Other north south lines are drawn in east and west of the prime meridian.Using this Latitude-Longitude grid, any point on the Earths surface can be defined by a location.EquatorLatitudeLongitudePrime Meridian

ReferenceReferences LinesOr True North

Reference Meridians True NorthThe astronomical NorthThe axis about which the Earth rotatesAssociated with latitude and longitude Magnetic NorthVery unstable, handy for navigationAssumed Reference - For rough mapping work

MeridiansA line on the mean surface of the earth joining north and south poles is called meridian.

Geographic meridians are fixed, magnetic meridians vary with time and location.Relationship between true meridian and grid meridians

Reference MeridiansAre also associated with coordinate systemsUse a grid systemCan be treated as planar Cartesian system (x,y)

Common Types of Bearing True BearingThis type of bearing is used for mapping used Military and Army.Bearings are measured w.r.t. true north using a compass.Magnetic BearingThis type of bearing is used for engineering surveying and mapping.Bearings are measured w.r.t. magnetic north using a compass.

Whole Circle Bearing (WCB) or Azimuthal BearingQuadrental or Reduced Bearing (RB) WCB is the angle which a line makes with reference meridian, always measured from North in clockwise direction.

Reduced Bearing is the smallest angle which a line makes with reference meridian, measured either clockwise or anticlockwise.SYSTEMS OF BEARING

Reduced BearingsThe Reduced Bearing is always accompanied by letters that locate the quadrant in which the line falls (NE, NW, SE, or SW).

Reduced

R B

Computation of Reduced Bearings

Thus, the whole circle bearings (WCB) of the lines must be converted into reduced bearings (RB), as RB is used in most computational work.

Conversion of WCB into RB and vice-versa .

CompassMany types & shapes.Prismatic, Surveyor, Reflective & SilvaConsist ofMagnetised needleA non-ferrous or plastic boxA graduated 3600 circle andAn aiming point

Parts of a CompassSilva Compass

1. PRISMATIC COMPASS2. SURVEYORS COMPASS Types of Compasses generally used

Prismatic Compass It is a pocket size instrument used for measuring magnetic bearings.

Prismatic Compass

Parts of a Prismatic Compass

Description of Parts1- Prism Guard2- Window with Guards3- Luminous Patch4- Index Ring Clamp5- Index Glass7- Index Ring with graduations6- Graduated Compass Ring8- Prism9- Thumb Ring10- Viewing Aperture & Slit11- Luminous Night Lubber Line12- Day Lubber Line13- Sighting Line

Graduation in CompassDegree system - (3600 circle)North = 0/3600South = 1800East = 900West = 2700

Graduated Compass RingSynthetic, Translucent MaterialInverted graduations

Graduated Compass RingThe graduated ring 80 to 110 mm in diameter is made up of Aluminum.

It is divided into 360 equal parts.

The graduations are marked to half a degree.

The scale is inverted and can only be correctly viewed through the prism.

The PrismThe prism assembly is hinged. When the compass is opened, the prism is swung into the reading position over the index glass. The prism is also fitted to slides which enables it to be raised slightly for focussing.The graduations of the compass ring is seen though the viewing aperture of the prism. Within the compass, directly below the prism and beneath the compass card, is a luminous source against which the compass card can be read at night.

Prismatic CompassThe main difference between Prismatic and Surveyor Compass is that the Surveyor's compass is usually the larger and more accurate instrument, and is generally used on a stand or tripod. The prismatic compass is a small instrument which is generally hold in the hand for observing, and is therefore employed on the rougher classes of work. The graduations on this prismatic compass are situated on a light aluminum ring fastened to the needle. The graduations therefore remain stationary with the needle, and the index turns with the sighting vanes.

Prismatic CompassThe prismatic attachment consists of a 45 reflecting prism with the eye vane so as to view the magnify image of the graduations on ring situated perpendicular to eye. The prism can be moved up and down to provide an adjustment for focusing.The image of the graduations is seen through a small circular aperture in the prism mounting, and immediately above this aperture is a small V cut on top of the mounting, over which the vertical wire in the object vane may be viewed.

Prismatic CompassWhen the V cut, the vertical wire and the Ground point whose bearing is required are viewed in one line, the bearing is directly read off the graduated circle immediately underneath the vertical wire. The two circular coloured discs in front of the back vane are dark glasses which can be brought in front of the vane when solar observations are being taken.

Prismatic CompassZero of the graduations coincides with the south point of the needle.Since the circle is read at the observer's (rather than the target's) end, the graduations run clockwise from the south end of the needle (0 to 360), whereas in the surveyor's compass, the graduations run anti-clockwise from north.

Point compass in the direction you want to goSet the compass, and read the value that is touching the index arrow

Working with Compass

Centering Levelling Focussing Aiming at ground objectTaking observations

Read a magnetic bearingOpen the compass and swing the prism to the reading position.Hold compass steady so that graduated ring rotates freely.Look through sighting slit and align sighting line on the object to which a bearing is required.When graduated ring has come to rest, read the bearing through the viewing aperture on the prism.

Brunton Compass

Uses Mirror instead of Prism

Thumb LoopLanyard RingSighting SlotLensLuminous Bezel LineLuminous Magnetic ArrowFixed Index LineLuminous HeadingLuminous Sighting DotsSighting WireGraduated Straight EdgeFloating DialBezelBRUNTEN (LENSATIC) COMPASS PARTS and Features of a Lensatic compass

Sighting Wire - front sight used with rear sight, for sighting landmarks for azimuth headings.Luminous Sighting Dots used in low-light condition and night navigation. Also a visual queue on aligning your body with the compass during night navigation.Graduated Straight Edge - upper half of a standard 1:50,000 scale map ruler, for measuring distances on a map.

LENSATIC COMPASS Cover - Protects the floating dial and other parts of the compass when closed.

LENSATIC COMPASS Base - The main body of the compass. If, for any reason, the lensatic compass were to malfunction, the base would be the piece that you would want to still work.Bezel Ring device clicks when turned; full 360 rotation is 120 clicks; each click equals 3.Luminous Bezel Line Used to mark a course direction during day or night navigation. Floating Dial black scale (mils), red scale (degrees), set in a deep tub for global use.Luminous Heading to read azimuth heading in low-light or night conditions.Luminous Magnetic Arrow always points to magnetic north.Thumb Loop to hold compass with the thumb. Fixed Index Line azimuth heading.Lanyard Ring for string or rope.

FLOATING DIAL SCALEBLACK RINGMils - is used mainly in artillery, tank, and mortar gunnery. AND is also used for very accurate azimuth land navigation. 6400 Mils to a Circle Distance Between Small Marks = 20 Mils Distance Between Big Marks = 100 Mils Distance Between Numbers = 200 MilsN = 64 (6400)E = 16 (1600)S = 32 (3200)W = 48 (4800)8.89 Mils = Degree17.78 Mils = 1 Degree

LENSATIC COMPASS

Degrees common unit of measure is the degree ().

360 Degrees to a Circle Distance Between Red Marks = 5 Distance Between Big Marks = 10 Distance Between Red Numbers = 20 N = 0E = 90S = 180W = 270BLACK RINGRED RINGFLOATING DIAL SCALEMils - is used mainly in artillery, tank, and mortar gunnery. AND is also used for very accurate azimuth land navigation. 6400 Mils to a Circle Distance Between Small Marks = 20 Mils Distance Between Big Marks = 100 Mils Distance Between Numbers = 200 MilsN = 64 (6400)E = 16 (1600)S = 32 (3200)W = 48 (4800)8.89 Mils = Degree17.78 Mils = 1 Degree

Keep Eye Vane towards you and Object Vane towards Ground Object.Hold the Compass firmly.Sighting Through a Lensatic Compass

Sighting Through a Lensatic Compass

Sighting Through a Lensatic Compass

SIGHTING LENSATIC COMPASSModule 1 Lensatic CompassPART 1 Basic Land Navigation

SIGHTING LENSATIC COMPASSModule 1 Lensatic CompassPART 1 Basic Land Navigation

SIGHTING THROUGH A LENSATIC COMPASS

Sighting Through a Lensatic Compass

65 BearingSighting Through a Lensatic Compass

Types of Bearing Fore BearingBack Bearing

FB and BBThe line AB has a bearing of N 62o 30 E (FB)BA has a bearing of S 62o 30 W (BB)Reverse DirectionsReverse Bearings

LineBearingABN 62o 30 EBAS 62o 30 W

Back BearingA back bearing is the bearing immediately opposite to the direction of travel.Add 1800 if bearing is smaller than 1800Subtract 1800 if bearing is larger than 1800

Azimuth Reverse DirectionThe line CD has an azimuths of 128o 20DC has an azimuths of 308o 20 To reverse azimuths: add 180oReverse Azimuth Bearings

LineAzimuthsCD128o 20DC308o 20

Compass Survey of an AreaMark corners of the Area to be surveyedTake Bearing from first corner (A) to second (B) (Fore Bearing)Shift at Point B - take a Bearing to Point A (Back Bearing)Continue each subsequent points in this way

Other Methods of Finding Direction By shadow stick By sun observationsBy stars observationsBy GPS

Diagonal Eyepiecefor astronomical observations

Diagonal EyepieceThe diagonal eyepiece is required for sights to the zenith (for example, in field astronomy), when the horizontal plate obstructs access to the telescope and circle-reading eyepieces. The eyepiece is attached to the telescope. It deflects the line of sight through 90, so that the observer views the images from the top or side of the telescope.When changing from one telescope position to the other, they can be reversed. The regular eyepiece of the telescope is unscrewed and replaced with these diagonal attachments.

Bearing1. Included Angle - the difference between two directions (Bearings)

2. Magnetic Declination Horizontal angle between true and magnetic North.

Geographic (True) North

North PointsTrue north - TNEarth spins on this axis

Magnetic north - MNCompass needle points to magnetic north

Magnetic MeridiansDefined at a point by earths magnetic lines of force

Magnetic declinationIt varies with location on earth

Magnetic VariationMagnetic variation:Variation between grid and magnetic north.Four types of magnetic variationDiurnal variation (upto 12 minutes)Annual variation (0-2 minutes)Secular variation (150-250 years)Irregular variation (due to storms, volcanic eruptions, earthquakes etc)(1-2 degree)

Difference between True Bearing and Magnetic Bearing

If magnetic bearing is greater than true bearing - westIf magnetic bearing is less than true bearing east

Compass is considered calibrated once variation is determined.

Conversion of bearingsTo convert Magnetic north into True north or vice versa, it is necessary to add or subtract the Magnetic Declination angle.When magnetic north is west of True north, subtract the magnetic declination angle.When magnetic north is east of True north, add the magnetic declination angle.True Bearing = Magnetic Bearing Mag. Dec. (E/W)

ExampleTrue NorthMagnetic Declination 30 WestAB

Local AttractionLocal disturbances due to magnetic field

Usually constant at a pointLocal Attraction are the local forces which affect a freely floating magnetic needle.

Local Magnetic AttractionSmall Metal ObjectsObjects such as buttons, rings or wristwatches can affect the accuracy of a magnetic compass. These small objects introduce relatively small error; their presence tends to be easily overlooked. To ensure accurate readings, these small metal objects must be removed from the person. Radio remote control units may seriously affect compass readings.

Local Magnetic AttractionLarge Metal Objects:These cannot be readily removed, the observer must maintain a safe distance from them.Example Magnetic rocks or iron ore, Steel Structures, rails, Iron Pole, Electric Line, Pipe Line etc.

Corrections due to Local Attraction .Stations A and B are free from LA while Stations C and D are affected from LA

Computation of Bearings in a Traverse

Computation in a Traverse1.Measure the bearings (Back and Fore) of the first traverse line (PT and PQ). Similarly measure the bearings (Back and Fore) of remaining traverse lines.Compute the included angles between the traverse lines. Calculation of closing error. Adjust the error.

Counterclockwise Direction (1)StartGiven

Counterclockwise Direction (2)

Counterclockwise Direction (3)

Counterclockwise Direction (4)

Counterclockwise Direction (5)FinishCheck

StartGivenFinishCheck

Clockwise Direction (1)StartGiven

Clockwise Direction (2)

Clockwise Direction (3)

Clockwise Direction (4)

Clockwise Direction (5)FinishCheck

StartGivenFinishCheck

Azimuths ComputationCounterclockwise direction: add the interior angle to the back azimuth of the previous course

Azimuths ComputationClockwise direction: subtract the interior angle from the back azimuth of the previous course

Bearing ComputationComputation can proceed in a Clockwise or counterclockwiseSketch for Bearings Computations

Comments on Bearing and AzimuthsAdvantage of computing bearings directly from the given data in a closed traverse, is that the final computation provides a check on all the problem, ensuring the correctness of all the computed bearings

Sketch for each Bearings Calculation

Comments on Bearing and AzimuthsDisadvantages associated with computing bearings directly from the data in a closed traverse is that there is no systematic approach to the overall solution. Each bearing computation is unique, requiring individual analysis.

Comments on Bearing and AzimuthsThe computation of azimuths involves a highly systematic routine: add (subtract) the interior angle from the back azimuths of the previous course.

Summary of Results from clockwise and counterclockwise approaches

Computation of Bearings in a Traverse using Deflection AngleTsRNQAnti clockwise traverse P

Compute Bearings of Remaining Traverse Lines from Deflection Angles W.C.B. of a traverse line = W.C.B. of the preceding line deflection angle. Use plus (+) for the right defection angles and minus (-) for the left deflection angles. If the computed W.C.B. is more than 360, subtract 360, and if the result is negative add 360 to get the W.C.B. Check W.C.B. of the last traverse line = W.C.B. of the starting line + (right defection angles) - (left deflection angles)

Bearing PQ = 130Bearing QP = 130+180 = 310 Bearing QR = 310+120 = 430It is greater than 360 thenBearing QR = 430-360 =70 Bearing RQ = 70+180 = 250 Bearing RS = 250+50 = 300 Computation

Sum of all Interior Angles = (2n-4) 90

For a 5 sided traverse Sum of all Angles = (10-4)90 = 5400

Permissible closure error = 20n = 205 45 Adjustment of a Traverse

Compass Error Instrument Errormisalignment of Vane, Peep-site, Wireinaccurate tic marks on compass circle External Errorlocal influences or local attractionUser Errorcompass not flat or moving

Advantage of a Compass

error limited to individual readingsnot compounded from previous reading

THE END

Taking a Grid BearingUsing a compass & map.Place edge of compass along intended bearing.Direction arrow points the way you want to travelTurn housing so meridian lines are parallel to easting linesRead grid bearing where housing and index intersectNote: This bearing must be converted to mag bearing if intended for field use.TIPIgnore the needle whenusing compass as aprotractor

ApplicationMagneticBearingPlus Compass Variation EastLess Compass Variation WestGrid Bearing

Magnetic Bearings contCompass back bearingsFace the opposite direction, turn compass around & walk with directional arrow pointing towards you.Or use white needle as directional indicatorTIPThe desk youre sitting at has local magnetic attractionCompass ErrorIndividual compassesLocal magnetic attraction due to steel/iron oreTransmission lines = 80mCar = 60mWire fence = 10mPick, Axe or shovel = 3m

Bearings - Cont N A 37

0 N

75 b 0 N A X 31 B

0a = 37 0 0b = 75 AB = 31 if A is specified 0c = 304 N

C 304 0

Magnetic BearingsSetting a Magnetic bearingHold compass flat in palmSet bearing on compass by rotating housingTurn yourself till red needle lines up with northNow walk in direction of directional arrowTaking a Magnetic bearingHold compass with directional arrow pointing at intended object/directionRotate housing till north aligns with red arrowRead bearing where index lines intersects

Magnetic VariationThe difference between grid north & magnetic north is called magnetic variation.The magnetic north pole is not fixed, it moves continuallyEasterly & westerly variationCheck map for accuracy of variation

Converting BearingsMag bearings must be converted to Grid bearings for plotting.Grid Bearings taken from map must be converted to Mag for compass workTo convert bearings simply add or subtract variationGMS = Grid to Magnetic Subtract (GrandMa Sux)MGA = Magnetic to Grid Add (My Green Apple)Grid bearings are always larger than a magnetic bearing with an easterly variation

Prismatic CompassWhen the V cut, the vertical wire and the Ground point whose bearing is required are viewed in one line, the bearing is directly read off the graduated circle immediately underneath the vertical wire. The oblong mirror located in front of the forward vane slides up and down the vane, and is hinged to fold flat over it or to rest inclined at any angle with it. This mirror is used for solar observations, or for viewing any very high object, and is not a normal fitting to a compass. The two circular discs in front of the back vane are dark glasses which can be swung in front of the vane when solar observations are being taken.