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Transverse/offset survey

Transverse/offset survey. To survey the field ABCDE: Choose any suitable diagonal, ie AD Measure the lengths along the transverse line , ie AP, PQ, QR and RD. Measure the lengths of the offsets , ie BQ, CR and EP. 20+27=47. Field diagrams.

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Transverse/offset survey

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  1. Transverse/offset survey • To survey the field ABCDE: • Choose any suitable diagonal, ie AD • Measure the lengths along the transverse line, ie AP, PQ, QR and RD. • Measure the lengths of the offsets, ie BQ, CR and EP.

  2. 20+27=47 Field diagrams When in the field doing the survey the surveyor sketches the information as a field diagram. • To complete a field survey: • Start at one end of the transverse line • Write down the cumulative distances of the offsets from the starting point • Write down the lengths of the offsets. • Units are not shown.

  3. Plane table radial survey • When doing a plane table radial survey you normally: • Place a table towards the middle of a field • Mark a point towards the middle of the paper. • From this point draw a line towards each corner of the field • Measure the distance from the point towards the middle of the paper to each corner of the field • Note • The angles at which the lines are drawn are important as this is used in doing an accurate scale drawing, • It is called a radial survey as all lines “radiate” out from the centre. • The point O is often used as the centre point

  4. A D 23m 28m 87º 81º 68º 19m 33m O C B Example 1 The diagram shows the results of a radial survey of a field ABCD

  5. Compass radial survey • A compass radial survey is similar to a plane table survey: • Stand towards the middle of a field, • Take a compass bearing of each corner of the field, • Measure the distance from the point you are standing to each corner of the field • Note • Only very rarely is one of the corners directly north, • Often the angle asked for involves the corners just to the left and right of due north.

  6. G 318º E 053º N 49m 29m O 35m F 197º Example 2 The diagram shows the results of a radial survey of a field EFG

  7. Today’s work • There are two ‘fields’ marked on the oval. • Create a radial and compass survey/diagram of each of the ‘fields’. • On ‘field 1’ use radiating lines (and protractors) and the navigational compass. • On ‘field 2’ use the giant protractor and the iphone. • Use your surveys to find the area of the ‘fields’. • Equipment: pencils, rulers, rubbers, paper.

  8. A D x 23m 28m 87º 81º 68º 19m 33m O C B Example 1 The diagram shows the results of a radial survey of a field ABCD a) Find the size of BOC. b) Calculate the length of BC. c) Calculate the area of triangle OBC. a) BOC = = 360  68  81  87 = 124º Just type it in. c) Area = ½absinC = ½  19  33  sin124 = 259·9m2

  9. G 318º E 053º N 49m 29m O 35m F 197º Example 2 The diagram shows the results of a radial survey of a field EFG a) Find the size of GOE. b) Calculate the length of GE. c) Calculate the area of triangle GOE. a) NOE = = 53º NOG = = 360  318 = 42º GOE = = 53 + 42 = 95º c) Area = ½absinC = ½  49  29  sin95 = 707·8m2

  10. Today’s work • Exercise 6G pg 197 • #2a, 3a, 4, 5,

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