Theodolite
Theodolite
Theodolite
Theodolite Basics
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Contents
1. Theodolite features
2. Set up a theodolite
3. Check & adjust a theodolite
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1. Theodolite features
a. Optical Reading Theodolites
b. Electronic Reading Theodolites
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MICROMETER SCREW
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V.A. = 089 29 56
1 2 3 4 5
Keys
6 7 8 9 0
SET PWR
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Field of view
Field of
View
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0
33
0 30 The circle is graduated
32 40
50
0
30
60
Subdivisions of
290
70
degrees are minutes
280
80
and seconds.
270
90
260
100
The centre of the circle
250
110
defines the centre of
0
24
12
0
13
0
22
0
0
14
0 telescope
21 15
0
200 160
190 170
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Angles/Bearings
N
If Zero on the circle is aligned
with North, then the circle
readings are known as “Whole
N Circle Bearings”, or “Azimuths”.
32
0
33
0
340
350 0 10
20
30
40
0
31
50
0
30
60
B
290
70
280
80
270
90
260
350 0 10
100
0”
340 20
33
0 30
’ 0
250
8º 00
110
0
32 40
0
=
24
B ’ 00
12
0
31
WC
50
0
0 0
0
º
23
0
13
8
30
0
25
60
0
22 14
=
290
C B
0
70
21 15
0
W 200 160
280
90
260
A
100
250
110
0
24
12
0
0
23
13
0
0
22
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0
0
21 15
0
200 160
190 180 170
9
50
0
30
60
2 90
70
280
80
270
90
260
100
11 0
12
0
0
23
0
22 0
14
0
21 0
15
20 0 160
190 180 170
Theodolite features
• This is the end of the features section
• And the the start of the operating
section
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2. Operating a theodolite
1. Health, Security & safety
2. How to set up a theodolite
3. How to calibrate a theodolite
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R = 0.6m.
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Foot
screws
Raise or
Lower
R = 0.6m.
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Operating a theodolite
• This is the end of the operating section
• And the the start of the calibration section
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Test 1 - Damage
a) Obvious physical damage, (instrument
& accessories).
b) Water penetration, (cloudy optics).
c) Battery condition, (if applicable).
d) Does everything work properly?
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Test 2 - Plummet
Optical Plummet or Laser Plummet
+/- 2mm at 1.5 metres
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V. CIRCLE
0º 180º
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V. CIRCLE
V. CIRCLE
90º 270º
Allowable error is 2 divisions
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Detail pole
Supported
Bubble
Central
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A B C
This does NOT check errors proportional to the distance
Ideally check a known distance
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Practical Exercise
• To test your learning you will be required to
set up a theodolite over a point and calibrate
the instrument.
• This is a test for each student individually.
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THE END
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Slide 1
• Angles are measured using the sexagesimal system.
• A circle is divided into 360 degrees.
• A degree is further divided into 60 minutes.
• A minute is further divided into 60 seconds.
Slide 3.
• It is advisable to learn on an optical reading theodolite before progressing to
electronic reading theodolites.
• If you can use an optical reading theodolite, you can use electronic reading
theodolites.
• Optical reading theodolites are still widespread in Industry.
• The only difference between an electronic theodolite and a conventional
theodolite is the reading and angle setting system.
-
Slide 4
• This is the view through the reading eyepiece.
• I have coloured blue the items which move when the micrometer screw is
rotated.
• To set the horizontal angle to a certain value is an involved procedure.
• To read the angles is not easy. This is one of the easier ones. (Pentax).
• Turn the micrometer knob until the movable (blue) lines are central on the
static black lines.
Slide 5
• To set the horizontal angle to a certain value is very easy.
• To read the angles is also very easy.
Slide 6
• This is what you see when you look through the telescope.
• The field of view is reduced for spectacle wearers.
• The central vertical X hair is the reference for the horizontal angle.
• The central horizontal X hair is the reference for the vertical angle.
• The small X hairs subtend an angle of 0.573 degrees, i.e. 1/100.
• (In this case, 1.771 – 1.349 = 0.422. Therefore the distance is 0.422*100 =
42.2 metres).
Slide 7
• This is a birds-eye view of the horizontal circle. The circle is mounted
horizontally and is used to measure angles in the horizontal plane.
• The circle can be clamped to either the upper rotating part of the theodolite, or
the lower fixed part.
• If the circle is clamped to the fixed part, the reading changes as the theodolite
rotates.
• If the circle is clamped to the rotating part, the reading does not change as the
theodolite rotates.
• In this way, the reading can be set to a required value, and the theodolite then
aligned with an object corresponding to that value.
• It is not possible for a theodolite to automatically align itself with North. If this is
required it must be done by the operator using one of several methods.
• To measure “Whole Circle Bearings” also called “Azimuths”, or “Headings”, it
is necessary to align zero on the horizontal circle with North.
Slide 8
• Correct Surveying terminology is “Whole Circle Bearing”, or “Azimuth”.
• Navigation terminology is “Heading”.
• “Bearing” is often used but should be avoided due to confusion with “Quadrant
Bearing”, (Points of the compass).
Slide 9
• This circle is mounted vertically and is used to measure angles in the vertical
plane. Zero is at the top.
• The centre of this circle defines the centre of rotation of the telescope.
• The vertical axis of the theodolite is determined by a straight line from the
centre of the earth, through the centre of the theodolite, to the Zenith, i.e. a
“Plumb Line” and is determined by an internal pendulum device called a
”compensator”.
• Angles in the vertical plane are always measured from the Zenith.
• As you can see, the line of sight is horizontal when the circle reading is 90
degrees, or 270 degrees.
Slide 13
The procedure.
• Extend the tripod legs to no more than your toe to collarbone distance.
• Place the tripod centrally over the ground point.
• Position the points of the legs about 0.6 metres from the ground point, and
equally spaced from each other.
• Press the tripod legs into the ground using the foot pegs.
• Ensure all clamps are tight.
• Remove the theodolite from its box, and screw onto the tripod.
• Close the lid of the theodolite box to keep out rain & dust.
Slide 14
• Position the plummet beam or X-hairs on the ground mark, (+/- 25mm.) by
rotating the foot screws or by moving one tripod leg at a time.
• Press the tripod legs into the ground using the foot pegs.
• Centralise the circular bubble by increasing or reducing the length of each
tripod leg in turn, while keeping your foot on the foot peg of the tripod leg you
are adjusting.
• Repeat for each tripod leg in turn until the circular bubble is central.
• Do not move the points of the tripod legs off the ground.
• When the circular bubble is central, position the tubular bubble parallel to two
foot screws, and centralise it by turning these two foots crews by equal
amounts, but in opposite directions.
• Turn the theodolite 90 degrees horizontally, and using only the remaining foot
screw, centralise the tubular bubble.
• Ensure that the bubble remains central for any rotation of the theodolite.
• Minor adjustment of the foot screws might be required to achieve this.
Slide 15
• Slacken the bolt holding the theodolite to the tripod, and while looking through
the optical plummet, or observing the laser spot, slide the theodolite on the
tripod top until the ground point is bisected, and tighten the bolt.
• The theodolite must not be rotated during this sliding activity.
• Check that the theodolite is still level, and make any minor corrections using
the foot screws.
• Check that the ground mark is still bisected, and if not repeat the sliding
procedure until it is.
The set up is satisfactory when: -
• The ground mark is bisected +/-1mm.
• The tubular bubble does not move more than one division in a 360 degree
rotation.
• All four tripod clamps are tight.
• The tripod is not causing an obstruction.
• The tripod is in no danger of being knocked.
• The observer is in no personal danger.
Slide 17
• It is important that checks are done in the order shown.
Slide 18
• Check this list above and terminate the calibration checks if the instrument
fails. Label the instrument “Do not Use”, and arrange for a replacement.
• Proceed to the next stage on satisfactory completion of the damage checks.
Slide 19
• The Plummet is used to position the theodolite over a ground point, (either a
Survey Station or a Grid Intersection).
• An Optical plummet requires the operator to focus on a ground point using a
built-in eyepiece as shown. Focussing adjustment is provided at the eyepiece.
• A Laser plummet has no eyepiece. A built-in laser projects a beam downwards
to a ground point. Intensity regulation is provided.
• The line of sight or laser beam must be concentric with, and parallel to, the
centre of the bearing as shown.
• To check that this is so, bisect the ground point with the crosshairs or laser
beam of the plummet, then rotate the theodolite 180 degrees in the horizontal
plane.
• If the ground point is still bisected +/- 1mm. The plummet is in adjustment.
• Correction of errors is detailed in the manual for each instrument.
• Repeat this check after adjustment.
• It is not necessary for the theodolite to be level for the purpose of this test.
Slide 20
• When the main tubular bubble is central, the vertical axis of rotation of the
theodolite must be vertical.
• Position the bubble parallel to two foot screws.
• Turn the foot screws equally, but in opposite directions until the bubble is
central.
• Turn the instrument 180 degrees horizontally.
• If the bubble is still central no adjustment is needed.
Slide 21
• Repeat the above at the 90 degree & 270 degree positions, but using only the
third foot screw.
• The bubble should remain central for any horizontal orientation of the
theodolite.
• If adjustment is required, half the error should be removed by rotating the foot
screws and half by the adjustment screws. Refer to the instrument manual.
• Repeat this check after adjustment.
Slide 22
• The line of sight of the telescope must be at 90 degrees to the horizontal axis
of the theodolite.
• Tests 4 & 5 require measurements on two faces of the theodolite
Slide 23
• V Index error is the error between the plumb line and the vertical axis.
• H index error is when the angle between the line of sight and the tilting axis is
not a right angle.
• T Axis error is when the tilting, (trunnion), axis is not horizontal.
Slide 24
• A line connecting zero and 180 degrees on the vertical circle must be vertical.
• See the manufacturer’s manual for adjustment procedures.
• Repeat this check after adjustment.
Slide 25
• See the manufacturers manual for adjustment procedures.
• Repeat this check after adjustment.
Slide 26
• The instrument must be precisely level for this test.
• Adjustment is normally only provided for trunnion axis dislevelment on high
precision instruments.
Slide 28
• Roll the detail pole on a kitchen counter top or similar flat surface.
• The detail pole must be rigidly supported at the top
Slide 29
• A, B, and C must be in a straight line, say 10 meters apart.
• Ideally use three tripods and two targets.