Unit 4 Plane Table Surveying Unit 4 Plane

Unit 4. Plane Table Surveying Unit 4: Plane table surveying

Topics covered Ø Ø Ø 1/30/2022 Definition, general accessories of P. T. , operations of P. T. Orientation - by compass, by back sighting Methods of plane tabling - Radiation, Intersection, and Traversing. Advantages & Disadvantages of plane table surveying. Errors in P. T. Unit 4: Plane table surveying 2

4. 1 Definition, Accessories & operation of P. T. What is plane table surveying? Ø Ø Graphical method of surveying Skips one intermediate steps of recording measurement Where it fits? Ø Ø For detailing purpose once the traverse is laid out Speed is important than accuracy 1/30/2022 Unit 4: Plane table surveying 3

4. 1 Accessories of P. T. Plane table Ø Ø Traverse (small in size) Johnson ( 45× 60 cm or 60× 75 cm ) v v Ø Ball & socket joint Upper & lower screw Survey coast v v v 1/30/2022 For precise work Levelling through foot screw Clamp & tangent screw Unit 4: Plane table surveying 4

4. 1 Accessories of P. T. Alidade Ø Pain alidade Alidade Ø v For ordinary survey Telescope alidade v v 1/30/2022 Limitation in slope Superior quality Telescope used to sight For accurate surveying Unit 4: Plane table surveying 5

4. 1 Accessories of P. T. Plumbing fork Ø Ø Centring purpose Consists of hair pin –shaped light metal frame Spirit level Ø Ø To ascertain if the table is properly levelled Place the level in two different position perpendicular to each other 1/30/2022 Unit 4: Plane table surveying 6

4. 1 Accessories of P. T. Trough compass Ø Used for orientation purpose Drawing paper Ø Ø Ø Should be superior quality For precise work, two sheets are mounted with their grains perpendicular to each other For very precise work, fibre glass sheet is used 1/30/2022 Unit 4: Plane table surveying 7

4. 1 Operation of P. T. surveying involves 3 steps of operation Fixing Setting Ø Ø Ø Levelling the table Centring Orientation Sighting the points 1/30/2022 Unit 4: Plane table surveying 8

4. 2 Operation of P. T. Orientation Ø Ø Process of putting table such that the direction of line on table is parallel to that in the ground Essential condition when there is more than one station Orientation disturbs the centring For precise work, repetition of orientation and shifting of table is necessary Methods Ø Ø By trough compass By back sighting 1/30/2022 Unit 4: Plane table surveying 9

4. 2 Operation of P. T. Orientation by trough compass Ø Ø Less accurate method Used when there is no second point for orientation When speed is more important than accuracy For approximate orientation prior to accurate orientation Orientation by back sighting Ø Precise method of orientation Sighting the points 1/30/2022 Unit 4: Plane table surveying 10

4. 3 Methods (Systems) of Plane Tabling Radiation Intersection Traversing Resection The first two methods for locating details whereas second two for locating plane table station 1/30/2022 Unit 4: Plane table surveying 11

4. 3 Methods (Systems) of Plane Tabling Radiation Suitable Ø Ø Ø when one single station can control the details to be located When distance between the station and details are short. Wider scope if distance can be computed tacheometrically with telescope alidade. 1/30/2022 Unit 4: Plane table surveying 12

4. 3 Methods (Systems) of Plane Tabling Intersection (Graphic triangulation) Used when distance between station and details is either too long or can’t be measured accurately. Needs at least two plane table station Only base line is measured Details are plotted by intersection of rays. 1/30/2022 Unit 4: Plane table surveying 13

4. 3 Methods (Systems) of Plane Tabling Traversing Same as radiation but locate the survey station If there are n number of station, plane table will have to be set on at least (n-1)stations to know the error of closure The traverse can be completed even by setting on (n-2) stations 1/30/2022 Unit 4: Plane table surveying 14

4. 4 Advantages and disadvantages of Plane Table surveying Advantages Ø Ø Ø Ø No possibility of omitting the necessary measurements Enables comparision of map and ground on the spot Less distance measurement No chance of data recording mistakes Useful in magnetically influenced zone Simple, cheaper than other methods No high skill required for job 1/30/2022 Unit 4: Plane table surveying 15

4. 4 Advantages and disadvantages of Plane Table surveying Disadvantage Ø Ø Ø Inconvenience for reproduction of map in different scale Not accurate method of survey Can’t be used in rainy and wet climate Use of many equipment. Heavy equipment, inconvenient to transport 1/30/2022 Unit 4: Plane table surveying 16

4. 5 Errors in Plane Tabling Error depends upon several factors Ø Ø Ø Quality of instruments available Speed of work aimed Character of survey 1/30/2022 Unit 4: Plane table surveying 17

4. 5 Errors in Plane Tabling Sources of errors Ø Ø Ø Instrumental Errors of plotting Personal v v v 1/30/2022 Non-horizontality of table Defective sighting Defective orientation Inaccurate centring Movement of board between sighting Unit 4: Plane table surveying 18

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