If the conical end of plumb bob lie exactly over the station (X is marked over station for accuracy), the compass is considered to be exactly centered. It is equipped with vertical sights for aiming at a distant object. To determine the bearing of the surveying line of sight. [gravityform id="1" title="false" description="false" ajax="true"]. If the magnetic north is east of grid north the variation is added to the magnetic bearing). Irregular paths (or boundaries) should therefore be first divided into straight segments before readings are taken. Try not to wear too many jewellery or rings as the metals can interfere with the compass readings. Reduced Bearing: When the whole circle bearing of a line is converted to quadrantal bearing it is termed as a reduced bearing. The bearings of survey lines in a traverse are observed in progressive way. Compass rule. 5.23) and measure length AB to the scale. a. By Included Angles 3. Procedure for Undertaking Prismatic Compass Survey. Magnetic meridian: When the magnetic needle is suspended freely and balanced properly, unaffected by magnetic substances, it indicates a direction. Join A and B2, which represents the direction of AB. Try not to wear too many jewellery or rings as the metals can interfere with the compass readings. If it does not, discrepancy is said to be the closing error. The compass is turned so that line of sight is aligned in the direction of AB by making eye slit of observation vane, vertical hair of object vane and ranging rod at B in same horizontal line. Set a marker on the ground at Point A. Parts of Surveyor Compass. The compass is set so that its centre lies exactly above the station under consideration. As a rule, if the forward azimuth is greater than 180o, you should subtract 180 from the forward azimuth to get the back azimuth but if the forward azimuth is less than 180o you should add 180 to it to get the back azimuth. Presentation | 7. Second Method: Unaffected line is first detected. This is achieved by suspending a plumb bob from the centre hook provided. The local presence of magnetic rocks, iron ore deposits, steel structures, railway lines, iron electric poles etc. In this method, the angle between the various lines are plotted by geometrical construction with the aid of table of natural sines. The needle is found to be inclined towards the pole. Keep your note book entries for you shall use it to plot the shape of land you measure in the field. Centring is done by adjusting the legs of the tripod. The compass or bow ditch rule which has named after the distinguished American navigator Nathaniel bow ditch (1773-1838) The compass rule is based on the assumption that all lengths wee measured with equal care and all angles taken with approximately the same precision. Load the file in Map Maker (Add Layer), Home Page | 0. Some priorities for compass surveying are as following-. Compass surveying is an important branch of surveying which is usually adopted in determining the position of an object both by angular and linear measurements. The measurement of the horizontal angle is accomplished using a pair of sights located on the north-south axis of the compass. Essay on Classification of Filters | Water Treatment | Water Engineering, Unconventional Machining Processes: AJM, EBM, LBM & PAM | Manufacturing, Material Properties: Alloying, Heat Treatment, Mechanical Working and Recrystallization, Design of Gating System | Casting | Manufacturing Science, Forming Process: Forming Operations of Materials | Manufacturing Science, Generative Manufacturing Process and its Types | Manufacturing Science. A Project Engineer, Whatever I learn on a day, I write it here... (BS) Developed by Therithal info, Chennai. 8      Now go to station 2 and let your partner move with the sighting pole to station 3. Levelling: Then at B, draw the angle ABC with the help of a protractor and cut off length BC to the scale. Then cut off BC according to the scale. Aiming for good visibility between stations and bearing in mind any subsequent setting out. Post was not sent - check your email addresses! A magnetic needle is provided which freely rotates over a brass circle. disturbance to the magnetic property of magnetic needle due to the presence of magnetic & electrical substances near the compass). The corners of the line may represent points whose positions it is wished to plot, or the polyline may describe the shape of a linear feature. Let AB be the survey line as shown in Figure , the bearing of which is required to be measured. From Point A take a compass bearing on Point B, then measure the distance between Point A and Point B. Having fixed suitably, the position of the starting point say A, draw a line representing the magnetic meridian. 9 . In the example provided the polyline is taken to represent the centerline of a path. It is basically a two-step procedure. Learn how your comment data is processed. Prismatic Compass Surveying PDF Notes Download, Prismatic Compass Surveying PDF Notes Download Click Below, Construction Residential Timeline Template Download, Bid Abstract Template for Construction Management. In this system, both north and south directions are used as reference meridians and bearings are reckoned either clock or anticlockwise, depending upon the position of the line. By Parallel Meridians through Each Station 2. The sight of the line is fixed and the reading is directly taken from the top of the glass cover. The position of the starting station say A is suitably selected on the sheet and the line AB is drawn parallel to the respective line and its length is cut off to scale. Plagiarism Prevention 5. This direction is known as magnetic meridian. The Compass: A compass can be used for: Measuring the angles in a traverse used for navigation or control purposes. Eye vane is used to observe the line of sight while on object vane image of the object is formed. Entry and display of survey data. Several trials can be needed for obtaining the correct centering of the compass. Following sample descriptions (Annex 16.2 - 16.5) on surveys are derived from an external document to support surveying procedures with import to Map Maker. b. The chord length B1B2 for the angle B1AB2 (the bearing of AB) is obtained from the table of chords or calculated by the relation, chord B1B2 = 2x 10.sin θ1 θ2. Carried out to determine and selection of suitable station points. Traversing: If it is wrong, redo the reading all over. Various mathematical tables give the lengths of chords of angles corresponding to unit radius. Quadrantal Bearing: The magnetic bearing of a line measured clockwise or anticlockwise from NP or SP (whichever is nearer to the line) towards the east or west is known as QB. This is also called the temporary adjustments of compass. Make some sketches if necessary, to portray the features and positions you find in the field. (ii) The liable error in the parallelism between all meridian lines are eliminated. View more posts. In the example provided the polyline is taken to represent the centerline of a path. It can be noted that back bearing of a line is equal to its fore bearing ± 180 o . Rationale | 1. The bearings shown in the table of survey data are grid bearings. The temporary adjustment of surveyor’s compass involves the following: The process of fixing the compass exactly over the station is known as centring. This bearing is called fore bearing of line AB. By Parallel Meridians through Each Station 2. Check to make any required chain and compass readings along the segment between stations 2 and 3 and then move on to the next segment. The bearings measured by prismatic compass are magnetic bearings measured with reference to magnetic north of the earth. b. This inclination of the needle with the horizontal is known as dip of the magnetic needle. Level of expertise required for this Chapter: Intermediate; general Map Maker training

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