Pack 11. Surveying processes. Equipment 11.1 Method 11.2 Using the recorded data to calculate the height of the building 11.3

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Kathleen Mosley
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1 Pack 11 Surveying processes Equipment 11.1 Method 11.2 Using the recorded data to calculate the height of the building 11.3

2 Pack 11 Surveying processes 11.1 Equipment The objective is to measure the height of a building using angles. You will find Building in the 21st Century, Chapter 2 useful. Theodolite Tripod Steel tape Wooden peg or surveyors pin Hammer or mallet Sharp metal spike if ground is hard Surveyors chalk 11.2 Method 1 Set up a peg at a suitable distance from the building (the governing factor will be the position of the telescope in relation to the instrument body). Suitable angle allows easy vision through the telescope Unsuitable angle prevents vision through the telescope Figure 11.1 If the peg is too close to the building the position of the telescope will not allow the surveyor enough space to look through it. A rough guide to distance would be about the same distance as the building is high, which will be about 45 or less from the horizontal. 2 Set up the tripod over the peg and roughly level the head. 3 Attach the instrument to the head of the tripod and secure it using the captivated screw. 2 Pack 11 Surveying processes

3 5p coin diameter 4 Stand back from the instrument to check its position in relation to vertical and the peg. It is important that the tribrach is approximately parallel to the instrument body and there is adjustment on all three foot screws. A good indication will be that the instrument body will appear vertical. Also ensure that the body of the instrument is central to the tripod head. 5 Check the alignment of the instrument with the centre of the peg or surveyors pin using either a plumb bob or the Figure 11.2 optical plummet. It should be within the circumference of a 5p coin from the centre. 6 Level up the instrument using the foot screws. Place instrument body parallel over two foot screws and rotate them both either inward or outward until the bubble is central to the marks. Then on certain instruments rotate the body 90 and adjust the third foot screw only. Rotate the body a further 90 and check alignment and repeat again for the final check. If the instrument is out of alignment (level) then adjust to half the error and repeat the checks until all errors have been eliminated. Pack 11 Surveying processes Zenith 0 Figure 11.3 Figure When all of the adjustments have been made the zenith (zero degrees) will be directly above the instrument. Check for parallax and adjust accordingly. Pack 11 Surveying processes 3

4 Pack 11 Surveying processes 8 Now target the top of the building using the gunsight scope on the top of the telescope. (It is normally four white arrows pointing to the centre or white triangles.) Keeping both eyes open align the gunsight with the target and lightly secure the horizontal and vertical clamps. Look through the telescope and use the slow motion screws to make fine adjustments and focus accordingly. Zenith 0 α 1 α 2 Lineal (distance) Figure Take and book the readings. Table 11.1 Angle Station Target/Comment V or H A Zenith Top of building α1 V Base of building α2 V m Lineal V = vertical angle, H = horizontal angle Using the recorded data to calculate the height of the building The information needs to be converted so that it forms two right angled triangles. 4 Pack 11 Surveying processes

5 Method The distance from the instrument to the building will be a lineal measurement in metres, in this case 35 m. That will be the adjacent of both triangles. Using the tan formula, an internal angle is required. Zenith 0 Pack 11 Surveying processes Opposite 1 α 1 α 2 Adjacent Opposite 2 Lineal (distance) Figure 11.6 Opposite 1 β 1 β 2 Adjacent Opposite 2 Lineal (distance) Figure 11.7 To calculate the internal angle of the upper triangle subtract α1from90 and label it β1. Pack 11 Surveying processes 5

6 Pack 11 Surveying processes 90 α1 = β = β1 = To calculate the angle for the lower triangle subtract 90 from α2. α2 90 = β = β2 = tan β = Opposite Adjacent Transpose the formula to put the unknown on the left of the equals sign. The upper triangle will be The lower triangle will be Opposite = tan β Adjacent Opposite 1 = tan Opposite 1 = m Opposite 2 = tan Opposite 2 = m Add Opposite 1 and Opposite 2 to give the height of the building = Answer: The overall height of the building is m. 6 Pack 11 Surveying processes

Pack 12. Surveying processes. Equipment 12.1 Method 12.2 Checklist 12.3 Calculations 12.4

Pack 12. Surveying processes. Equipment 12.1 Method 12.2 Checklist 12.3 Calculations 12.4 Pack 1 Surveying processes Equipment 1.1 Method 1. Checklist 1.3 Calculations 1.4 Pack 1 Surveying processes 1.1 Equipment The objective is to measure the height of an inaccessible building using angles.