Lecture 6--The Engineer's Transit and Theodolite

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The Engineer’s Transit and TheodoliteLecture 6GE10: General Surveying I

Department of Geodetic Engineering

University of the Philippines, Diliman

OutlineI. Engineer’s Transit

I. Main PartsI. Upper PlateII. Lower PlateIII. Leveling Head Assembly

II. Setting up the transitIII. Leveling of the TransitIV. Care of the Transit

II. TheodoliteI. Types of Theodolite

I. Repeating TheodoliteII. Directional TheodoliteIII. Digital Theodolite

II. Main Parts III. Setting up the theodolite

Engineer’s Transit

�Credited to Roemer, a Danish Astronomer, whoin 1690 used the instrument to observe thepassage (transit) of stars across the celestialmeridian

�Essentially a telescope and two large protractors

�1 protractor mounted in the horizontal plane andthe other in a vertical plane

�An instrument of precision

Main Parts

1.Upper Plate (or Alidade)

2.Lower Plate

3.Leveling Head Assembly

Main Parts of the Engineer’s Transit Parts of the Engineer’s Transit

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I. Upper Plate

�Consists of the entire top of the transit

�Entire assembly rotates about a vertical axis

�Contains the ff:�vertical circle and vernier

�standards: supports the telescope and level tube

� compass box

� circular cover plate and plate level vials

� upper clamp

� tangent screw

� needle lifter

1. TELESCOPE�Used for:

1. Fixing the direction of LOS2. Viewing the objects3. Magnification in the FOV

�Can be rotated about its horizontal axis

Direct position => level vial is above the telescope

Reversed position => level vial is below the telescope

I. Upper Plate

2. STANDARDS� Integral parts of the upper plate� Used to:

1. Hold into position the horizontalaxle level

2. Elevate or depress the telescope by rotating on an axis perpendicular to the

LOS

I. Upper Plate

3. COMPASS BOX

� Used to:

1. Establish magnetic meridian

2. Allow rough checks on measured angles� Magnetic needle can be lifted from its pivot by the

needle lifter

I. Upper Plate

4. PLATE LEVEL VIALS�Positioned at right angles to each other�Used to establish the upper and lower plates in ahorizontal plane

I. Upper Plate

5. VERTICAL CIRCLE�Attached to the telescope and rotates with it�Used to measure vertical angles

I. Upper Plate

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6. PLATE VERNIERS� Two opposite verniers (A & B)� A vernier is adjacent to theeyepiece where it is easily used

� B vernier is 180o from A vernier

I. Upper Plate

7. TELESCOPE CLAMP �Tightened to hold the telescope horizontal or atany desired inclination

� Located near the horizontal axle of the transit

I. Upper Plate

8.TELESCOPE TANGENT SCREW

� a.k.a. vertical circle tangent screw

� Enables the telescope to be rotatedin small movements about the horizontal axis when the telescopeclamp is tightened

� Useful when setting the cross hairs precisely on a distant point sighted

I. Upper Plate

9. UPPER CLAMP� A locking device � When tightened, it causes the

upper and lower plates to lock together

� Most have round heads and usually turn in the direction tangent to the motion they control

I. Upper Plate

10. OPTICAL PLUMMET� Small telescope thru the vertical center of the

transit� Enables the instrument to be centered over a

given point quickly and precisely by means of an optical system

I. Upper Plate

� Or horizontal circle� Where horizontal angles are measured� Graduated on its upper face and divided aroundits circumference into 360o and further subdivisions

� Can be held stationary while the upper plate isrotated or can be rotated independently

� As one unit, can be rotated also with the upper plate

� The underside is attached to a vertical and tapering spindle called the outer spindle

II. Lower Plate

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1. LOWER CLAMP� Attached to the horizontal

circle� Does not rotate with the

horizontal circle� Used to control the rotation of

the horizontal circle� Stops any motion between the

leveling head and the lower

plate

II. Lower Plate

2. LOWER TANGENT SCREW

� Used to make precise settings after the lower clamp is tightened

� It moves the lower plate to a desired exact position using a small range of movement

II. Lower Plate

� Lower part of the transit� Allows the transit to be leveled and centered overa point

� Consists of:1. bottom horizontal foot plate2. 4 leveling screws3. plumb bob chain4. a device that permits small lateral movements of transit

III. Leveling Head Assembly

1. LEVELING SCREWS� Used for leveling the

instrument by the plate levels� Operate in pairs and always

turned in opposite directions� Screws are loosened when

desired to shift transit laterally with respect to the foot plate


2. PLUMB BOB CHAIN� Chain with a hook:

� Suspended from the bottom part of the leveling headassembly

� Hangs between the tripod legs

� Used for attaching a string an a plumb bob sothat the instrument may be set exactly over theselected point on the ground

� Plumb bob string always hang vertical due to

gravity


SETTING UP THE TRANSIT

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1. On fairly level ground:� tripod is set up near and over the selected point with the

legs well spread apart to ensure stability

� see to it that the tripod head is nearly stable

2. On hillsides or along a slope:� 1 of its legs should extend uphill and the 2 downhill

� each tripod leg is then moved as required to make the tripod head nearly level

3. Set the tripod in a convenient height (no need to stretch or stoop)

1. POSITIONING THE TRIPOD

1. Remove the transit from its carrying case by grasping it with both hands at the leveling head assembly or at the upright standards

2. With one hand, screw the leveling head of the transit and firmly onto the tripod head while holding the standards at the other hand

3. The transit should fit snugly and bear firmly. 4. Remove the objective cap and replace with the

sunshade

2. MOUNTING THE TRIPOD

� Plumb bob and a string is attached to the transit bysuspending it from the hook and chain that hangs atthe bottom of the leveling head.

� Raise or lower the plumb bob using the sliding loop-knot

� Lower down the plumb bob within about 0.5 cm above the ground point

� Bring the plumb bob close to the center of the pointby moving or pressing 1 or 2 tripod legs more firmlyinto the ground

3. ATTACHING THE PLUMB BOB

� See to it that the wing nuts of the tripod is tightened

� Shift the leveling head of the transit along the foot plate to exactly center the plumb bob

� Use the optical plummet if available for accurate centering:� look at the optical plummet� shift the instrument until the reticle is precisely

centered on the ground point

4. FINAL CENTERING

LEVELING OF THE TRANSIT

LEVELING THE PLATE LEVEL BUBBLE

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1. The bubble is centered by rotating screws 1 and 2 in opposite directions� the rotations (see figure) will cause the bubble to

move from left to right2. Next, rotate the instrument so that the one end of the

bubble tube is aligned with the remaining screw3. Center the bubble in this position by rotating this

remaining screw4. The rotation indicated in the figure will cause the

bubble to move away from level screw 3


5. Return to the original position and check centering of the bubble.

6. Rotate through 180o so that end A of the bubble tube is on line with level screw .

7. Repeat the previous steps so that all bubble tubes are leveled in every direction.


CARE OF THE TRANSIT

1. Store the transit in its carrying case when not in use2. Remove the transit from the tripod and carry it in its

box when transporting in a vehicle or over a long walking distance

3. If it becomes went or damp, dry it off with absorbent cloth or preferably in sunlight

4. The objective lens should not be wiped as it is easily scratched� clean it by rubbing gently with a piece of soft cloth

moistened in alcohol or with a piece of lens paper� finish off with a camel’s hair brush

CARE OF THE TRANSIT

5. Protect the instrument at all times from any shock or sudden jolt� never allow the instrument to fall or drop

6. Hold the transit in the arms with the tripod sticking out to the side or behind NOT on the shoulderdo this when:

1. Carrying it inside a building2. There is danger of striking the instrument against

any obstructions

CARE OF THE TRANSIT

7. The transit should be lifted from the carrying case by grasping the standards and NOT by the telescope.

8. Tripod legs should be spread apart to make it stable.

9. Tripod shoes should be sunk firmly to the ground.10.It should never be left unattended because it may

be upset by passing vehicles, stray animals, playing children, wind or maybe stolen.

11.Avoid setting the transit on concrete slabs, boulders, and steel plates

CARE OF THE TRANSIT

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12.Graduated circles and verniers should not be touched with the fingers. This will tarnish their surfaces.

13.Tarnished surfaces should are cleaned by applying a thin film of oil which is left for a few hours and then wiped off with a soft clean rag.

14.Tighten clamps in a definite and firm manner, not too severe.

15.A waterproof cover for the transit should always be brought along in case of rains, showers and thunderstorms.

CARE OF THE TRANSIT

READING

TRANSIT VERNIERS

MAIN SCALE AND VERNIER

LEAST COUNT� Fineness of reading of the vernier and main scale� Determine by dividing the length of the smallest

division on the main scale by the total number of vernier divisions.

n

sLC =

where:

LC = Least Count

s = value of the smallest division on the main scale

n = no. of divisions on the vernier


LEAST COUNT (Example)


� A horizontal or vertical angle is read by finding the

graduation on the vernier scale which coincides with a graduation on the main (circle) scale used

� In case of double vernier, there will always be 2coincident line�1 for a CW angle & the other for a CCW angle

� The index mark of the vernier will show thenumber of degrees or fractional part of a degree(usually in multiples of 30, 20, 15 or 10 min) passed over on the main scale

� Additional fractional parts of a degree (to be addedto the main scale reading) are to be determined from the coincident graduation on the vernier

READING TRANSIT VERNIERS

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s = 30 min n = 30

LC = 30 min/30 � LC = 1 min

Readings:

CW: 178o30’+12’ = 178o42’

CCW: 181o00’+18’ = 181o18’

Check:

178o42’+ 181o18’ = 360o

READING TRANSIT VERNIERSTheodolite� The name given to the earliest version of a device to measure angles in the horizontal and vertical planes, designed and built in England in about 1725.

� Theodolite in the 1800’s were not capable of the ability to be transited or turned 1800 about its horizontal axis, although this capability was included in an instrument called transiting theodolite.

� In Europe, the name theodolite was retained; in the United States the term transit was kept.

Types of Theodolite

1. Repeating Theodolite

2. Directional Theodolite

3. Digital Theodolite

Types of Theodolite1. Repeating Theodolite:

� can measure a horizontal angle as many times as required by adding them successively on the graduated circle

� capable of accumulating angles on its horizontal circle by means of its upper and lower motions

� horizontal scales may allow horizontal angles to be read directly to 10 sec or 20 sec.

Types of Theodolite2. Directional Theodolite:

� Horizontal circle remains fixed during a series of observations

� Telescope is sighted on each of the points and directions rather than angles to these points are read on the circle

� Required horizontal angle is determined by calculating the difference of two observed directions

� A reading on a directional theodolite represents the mean of two diametrically opposed sides of the circle. It is equivalent to averaging the readings of the A and B verniers of a transit.

Types of Theodolite3. Digital Theodolite:

� Resembles very closely a standard theodolite since horizontal and vertical angles in a survey are measured in a similar manner.

� It can be combined with an EDM instrument and microcomputer to assemble into what is called a total station instrument or an electronic tachoemeter.

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Parts of a Theodolite Parts of a Theodolite

Parts of a Theodolite

Clamping screw for vertical circle

Adjustable mirror to illuminate vertical circle

Vertical circle tangent screw

Horizontal Clamp

Parts of a Theodolite

Clamping screw for vertical circle

Adjustable mirror to illuminate vertical circle

Vertical circle tangent screwInverter

knob

Reading

Microscope

Horizontal

Tangent

Screw

Horizontal Clamp

Parts of a Theodolite (Wild T2)Horizontal Circle Reading (Wild Theodolite, T2)

Reading:

= 94010’ + 02’44.4”

= 94012’44.4”

where 0.4” is estimated

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Horizontal Circle Reading (Wild Theodolite, T2) References:

Davis, R.E., et. al (1981). Surveying: Theory and Practice. USA: McGraw-Hill, Inc.

La Putt, J.P. (2007). Elementary Surveying. Philippines: National Book Store.

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Documents

Lecture 6--The Engineer's Transit and Theodolite