Unit - 5
Theodolite traversing
Theodolite survey:
- It is precise instrument for measuring angles in the horizontal and vertical planes.
- It is accurate method or instrument used for measuring horizontal and vertical angles.
- It can use in prolonging survey lines, and finding elevations etc.
- It is also used for levelling.
- The line of sight of instrument can be rotated 180 degrees in vertical plane about its horizontal axis.
Instruments:
Following are part of theodolite:
(1) Telescope
- Telescope in theodolite is used for focusing at which object piece and eye piece at other.
- It rotates about horizontal axis in vertical plane.
(2) Vertical circle
- It is fitted to telescope and more simultaneously.
- Graduation is there in each quadrant from 0 to 90 degree.
(3) Index frame
- It is also known as Vernier frame or t frame.
- It consists of two parts vertical and horizontal.
- Horizontal arm is used to measure Vertical angle.
- Vertical arm Culp’s to lock telescope at certain level.
(4) Standards
- They are the frames which support telescope and it is rotated about vertical axis.
- It is also called as A frame.
(5) Upper plate
- It gives support to standards.
- It consists of two Venire with magnifiers which are arranged diagonally
- Upper clamping screw with respect to tension screw which helps to fixing with the lower plate.
(6) Lower plate
- It contains scale on which 0 to 360 reading are graduate.
- It is also called as scale plate.
- It is attached to outer spindle.
- It consists lower clamping screw.
- If lower clamp is loosened and upper is tightened both plates can rotate together.
- if the procedure is reversed that is lower clamp is tightened and upper loosened and then upper plate is movable and lower plate is fixed.
7) Leveling head
- It contains two parallel triangular plates known as tri batch plates.
- Upper path that is upper tribrach used to level up per plates and telescope with help of levelling screw.
- Lower part i.e., lower tribrach plate and is attached through tripod.
8) Shifting head
- It contains two parallel plates which are right angle to each other with one of them is parallel to trunnion axis.
9) Tripod: -
- It is just stand for theodolite which mounted over it.
- Levelled position is required for tripod to give correct observations.
- Steel shoes are there at the end of tripod
- Steel shoes are there at the end of tripod leg.
- These legs hold the ground strongly
10) Plumb Bob
- It is cone-shaped weight attached or tie with long thread.
- These is used for entering of theodolite.
11) Magnetic compass: -
- It is in circular compass box in centre of upper plate and used for selecting meridian.
Key takeaways:
- It is precise instrument for measuring angles in the horizontal and vertical planes.
- It is accurate method or instrument used for measuring horizontal and vertical angles.
A theodolite is a precision optical device for measuring angles among distinctive seen factors within side the horizontal and vertical planes. The conventional use has been for land surveying, however they're extensively utilized notably for constructing and infrastructure construction, and a few specialized programs along with meteorology and rocket launching. It includes a portable telescope established so it may rotate round horizontal and vertical axes and offer angular readouts. These suggest the orientation of the telescope, and are used to narrate the primary factor sighted thru the telescope to next sightings of different factors from the equal theodolite position. These angles may be measured with accuracies right all the way down to micro radians or seconds of arc. From those readings a plan may be drawn, or gadgets may be located according with an current plan. The current theodolite has developed into what's called a complete station in which angles and distances are measured electronically, and are examine at once to laptop memory. In a transit theodolite, the telescope is brief sufficient to rotate approximately the trunnion axis, turning the telescope thru the vertical aircraft thru the zenith; for non-transit units vertical rotation is restrained to a constrained arc. The optical stage is from time to time wrong for a theodolite, however it does now no longer degree vertical angles, and is used most effective for leveling on a horizontal aircraft (all even though frequently blended with medium accuracy horizontal variety and course measurements).
Preparation for making sightings Main article: Temporary modifications of theodolites Temporary modifications are a fixed of operations vital in an effort to make a theodolite equipped for taking observations at a station. These consist of its putting up, centering, leveling up and removal of parallax, and are completed in 4 steps:
Setting up: solving the theodolite onto a tripod in conjunction with approximate leveling and centering over the station mark
Centering: bringing the vertical axis of theodolite right away over station mark the use of a centering plate additionally called a tribrach
Leveling: leveling of the bottom of the tool to make the vertical axis vertical commonly with an in-constructed bubble-level. Focusing: doing away with parallax blunders with the aid of using right focusing of goal and eye-piece. The eye-piece best calls for adjustment as soon as at a station. The goal can be re-centered for every next sightings from this station due to the special distances to the target.
Sightings: Sightings are taken with the aid of using the surveyor, who adjusts the telescope's vertical and horizontal angular orientation so the cross-hairs align with the favored sighting point. Both angles are examine both from uncovered or inner scales and recorded. The subsequent item is then sighted and recorded without transferring the location of the tool and tripod. The earliest angular readouts had been from open vernier scales without delay seen to the eye. Gradually those scales had been enclosed for bodily protection, and sooner or later have become an oblique optical readout, with convoluted mild paths to convey them to a handy location at the tool for viewing. The present day virtual theodolites have digital displays. Errors in size Index blunders The angles within side the vertical axis need to examine 90° (one hundred grad) whilst the sight axis is horizontal, or 270° (three hundred grad) whilst the tool is transited. Half of the distinction among the 2 positions is known as the index blunders. This can best be checked on transit instruments.
Horizontal axis blunders
The horizontal and vertical axes of a theodolite ought to be perpendicular; if now no longer then a horizontal axis blunders exists. This may be examined with the aid of using aligning the tubular spirit bubble parallel to a line among foot screws and putting the bubble vital. A horizontal axis blunders is gift if the bubble runs off vital whilst the tubular spirit bubble is reversed (grew to become via 180°). To adjust, the operator gets rid of 1/2 of the quantity the bubble has run off the use of the adjusting screw, then re-level, check and refine the adjustment. Collimation blunders
The optical axis of the telescope, ought to additionally be perpendicular to the horizontal axis. If now no longer, then a collimation blunders exists. Index blunders, horizontal-axis blunders (trunnion-axis blunders) and collimation blunders are often decided with the aid of using calibration and are eliminated with the aid of using mechanical adjustment. Their life is taken into consideration within side the desire of size method in an effort to put off their impact at the size effects of the theodolite.
Key takeaways:
The optical axis of the telescope ought to additionally be perpendicular to the horizontal axis. If now no longer, then a collimation blunders exists
Theodolite Traversing Theodolites can be of types (i) Transit Theodolite (ii) Non-Transit • In the transit theodolite, the telescope, the telescope may be resolved thru a whole revolution approximately its horizontal axis in a vertical plane
There are diverse forms of theodolites for extraordinary functions of various constructional works. Usually, 4 kinds of theodolites are makes use of in web website online works for extraordinary measuring points. Such as- Repeating Theodolite Directional Theodolite Electrical Digital Theodolite
Total Station To without a doubt saying, theodolites may be additionally categorized into types Primary Theodolite Electronic Digital Theodolite
Repeating Theodolite
This layout enables horizontal angles to be remade any quantity of instances and brought without delay at the tool circles. This form of units is restrained for places where the assist isn't steady, or place for the use of different such units is limited. Directional Theodolite Angles are acquired via way of means of deducting the primary route analyzing from the second one route analyzing. This reads instructions in preference to angles. The non-repeating tool has no minor motion. Electrical Digital Theodolite
Naturally translates and statistics horizontal and vertical angles. Eliminates the usual analyzing of scales on graduated circles Total Station The general Station comprises the features of a theodolite for measuring angles, an EDM for measuring gaps, virtual data, and statistics documentation. Examples of Total Stations are the Nikon DTM 801, Topcon, and Geodimeter four hundred series.
Primary Theodolite
Primary Theodolite may be types. Transit Theodolites: A theodolite is known as a transit theodolite as soon as its telescope can be transited i.e. circled via an entire revolution concerning its horizontal axis in the vertical plane. Non-Transit Theodolite In this kind, the telescope can not be transited. They are inferior in software and feature presently come to be obsolete. Electronic Digital Theodolite This sort of theodolite offers the really well worth of remark immediately in the viewing panel. The exactitude of this kind of tool varies in the order of 1" to 10". It has additionally types.
Vernier Theodolites:
For analyzing the graduated circle, verniers are used to accurate analyzing of measuring factors and this theodolite is called as a Vernier theodolite. Micrometer Theodolites: A micrometer offers to browse the graduated circle same be termed as a Micrometer theodolite. This Digital theodolite is likewise referred to as Modern Theodolite and might carry out the subsequent functions: Distance measurement Angular measurement Data processing Digital show of factor details Storing statistics is a digital area book.
Key takeaways:
Theodolite Traversing Theodolites can be of types (i) Transit Theodolite (ii) Non-Transit • In the transit theodolite, the telescope, the telescope may be resolved thru a whole revolution approximately its horizontal axis in a vertical plane
Measurement of horizontal angle
1) To measure angle of ABC, instrument is set to B.
2) Upper clamp is loosened and lower clamp is fixed.
3) Telescope is turned and Vernier A is a set O and Vernier B to 180°.
4) Now lower clamp is loosened and tightened scope is pointed to A and bisect ranging rod at A.
5) Now lower clamp is tightened and lower tangent screw is turned to perfectly bisect ranging rod at A.
6) Now upper clamp is loosened and telescope is turned clockwise to bisect the C which is tightened at upper clamp.
7) Now, Vernier reading A and B is noted.
8) Vernier A result in angle directly and Vernier B result reading by subtracting initial reading from final reading.
Measurement of vertical angle
1) The zeros of Vernier are set to 0 degree to vertical circle.
2) Telescope is den clamped.
3) Plate bubble are brought to center with foot screw and altitude bubble is brought to centre by clip screw.
4) Telescope in bisect to point A and measure the angle of elevation.
5) Finally reading of Vernier is noted and elevation angle is also noted.
6) Now, face of instrument is changed and point A is bisected again and reading are noted.
7) Telescope is lowered slowly and B is bisected to measure angle of depression.
Horizontal and vertical control:
Horizontal and vertical control are formed to create framework around other surveys can be adjusted.
Horizontal and vertical control surveys are used in accurate mapping projects in the construction of underground utility systems, and in roadways, power lines, tunnels.
Methods of horizontal and vertical control
Horizontal positioning | Vertical positioning |
a) Triangulation | a) Geodetic levelling |
b) Trilateration | b)Trigonometricheighting |
c) Traversing | c)Barometric levelling |
d) Astronomical positioning |
|
e) GPS |
|
Key takeaways:
1) To measure angle of ABC, instrument is set to B.
2) Upper clamp is loosened and lower clamp is fixed.
Definition = the technique wherein the attitude is measured in clockwise route for any variety of instances is called repetition technique. Usually six instances 3 repetition with face left and 3 with face right. Set up tool over Q and leveled with as it should be with telescope within side the regular position
- Definition: The method in which the angle is measured in clockwise direction for any number of times is known as repetition method.
- Usually six times, three repetitions with face left and three with face right.
- One should note that, the accuracy will not increase by increasing the number of repetitions beyond a certain limit.
Procedure:
- Set up the instrument over Q and level it accurately with the telescope in the normal position.
- Set the vernier A to 360°. Loosen the lower clamp direct the telescope to left hand ranging rod at P, and bisect it exactly by using lower clamp and lower tangent.
- The vernier readings should be the same.
- Loose the upper clamp and turn the telescope in clockwise direction and bisect the right-hand ranging rod at R exactly by using the upper clamp and upper slow-motion screw.
- Read both vernier. Let the mean reading be 30° 2' The object of reading both verniers is to obtain the approximate value of the angle,
- Leaving the verniers unchanged unclamp the lower plateand turn the telescope in clockwise direction bisect the ranging rod at P exactly with lower clamp and lower tangent screw. The reading on vernier should be same as before.
- Loose the upper clamp and turn the telescope in clockwise direction and bisect ranging rod at R exactly by using upper clamp and upper tangent screw
- The verniers will now read twice the value of angle i.e., 2 x 30° 2'.
- By leaving the verniers clamped at 60° 40' measure the angle third time.
- Read both the verniers. Read the final angle.
- The average angle with face left will be equal to the final reading divided by three.
- Change the face and make three more repetition as described above.
- Find the average angle with face right by dividing the final reading by three.
- By taking average of both the face horizontal angle PQR is obtained.
Elimination or minimization of errors by method of repetition:
Following errors can be eliminated or minimized by this method:
- The errors due to eccentricity of verniers and centers are eliminated by taking vernier readings and averaging the readings.
- The errors due to the imperfect adjustment of the line of collimation and the horizontal axis of the telescope are eliminated by face left and face right observation.
- The errors due to in accurate graduations are minimized by taking the reading on different parts of the circle.
Key Takeaways:
The method in which the angle is measured in clockwise direction for any number of times is known as repetition method.
The blunders may be removed through analyzing angles on each the faces and taking the suggest of the found values. The horizontal axis now no longer being perpendicular to the vertical axis: The blunders may be removed through analyzing angles on each the faces and taking the suggest of the 2 values.
Instrumental Errors:
Non-adjustment of plate degrees: If the plate degrees which aren't perpendicular to the vertical axis, are centered, the vertical axis of the tool isn't always made virtually vertical. As a result, the horizontal circle is willing and the angles are measured in an willing aircraft in place of in a horizontal aircraft.
The mistakes are delivered within side the measurements of each horizontal and vertical angles. The blunders is critical whilst the horizontal angles among factors at notably one of a kind elevations are to be measured. The blunders may be minimized through leveling the device almost about the altitude bubble.
The line of collimation now no longer being perpendicular to the horizontal axis: If the road of collimation isn't perpendicular to the horizontal axis, it's going to hint out the floor of a cone rather than a aircraft whilst the telescope is revolved within side the vertical aircraft. As a end result horizontal angles whilst measured among factors at broadly one of a kind elevations may be incorrect
The mistakes may be removed with the aid of using analyzing angles on each the faces and taking the imply of the found values. The horizontal axis now no longer being perpendicular to the vertical axis: If the horizontal axis isn't always perpendicular to the vertical axis, the road of collimation will now no longer revolve in a vertical aircraft whilst the telescope is raised or lowered. This reasons an angular mistakes each in horizontal and vertical angles. The mistakes may be removed with the aid of using analyzing angles on each the faces and taking the imply of the 2 values.
(iv) The line of collimation and the axis of telescope-stage now no longer being parallel to every other: If the road of collimation and the axis of telescope- stage aren't parallel to every other, the 0 line of the vertical verniers isn't a real line of reference and as a result, an mistakes is delivered within side the size of vertical angles. The mistakes may be removed through taking observations of the angles, one with the telescope everyday and the alternative with the telescope inverted, and taking the imply of the 2 values. (v) The internal and outer axis i.e. the axes of each the higher and decrease plates now no longer being concentric:
This makes the angles examine on cither vernier incorrect. The blunders is removed via way of means of studying each verniers and averaging the 2 values. (vi) The graduations being unequal: The blunders is minimized via way of means of measuring the angles numerous instances on one-of-a-kind elements of the circle and taking the imply of all.
(vii) Verniers being eccentric: The zeros of the verniers will now no longer be diametrically contrary to every other. An mistakes may be delivered if handiest one vernier is examine, however it's going to cancel itself if each verniers are examine and the imply taken. (viii) The vertical hair now no longer being precisely vertical: The mistakess is minimised through the usage of the part of the hair close to the horizontal hair for bisecting the signal.
Observational or Personal Errors: (i) Inaccurate Centering: This may be very not unusualplace blunders and is added in all angles measured at a given station. Its significance relies upon upon the period of the sight. It varies inversely because the period. The blunders is lots decreased via way of means of cautiously centering the tool over the station-mark. (ii) Inaccurate Levelling: The impact of this mistake is much like that of the mistake because of non-adjustment of plate levels. The blunders is critical while horizontal angles among factors at notably distinct elevations are to be measured. The blunders may be minimized via way of means of leveling the tool cautiously close to the altitude level. (iii) Slip: The slip may also arise if the tool isn't firmly screwed to the tripod-head or the transferring head isn't sufficiently clamped or the decrease clamp isn't well tightened. As a result, the observations may be in blunders. This may be averted via way of means of right care. (iv) Working incorrect tangent screw: This is a not unusual place mistake at the a part of a beginner. This may be prevented via way of means of right care and experience. Always perform the decrease tangent screw for a returned sight and the top tangent screw for a foresight. (v) Parallax: This blunders arises because of imperfect focusing. The parallax may be removed via way of means of well focusing the eye-piece and the object-glass. (vi) Inaccurate bisection of the factor sighted and non-verticality of the ranging rod: Care need to be taken to bisect the bottom factor seen at the ranging rod. In case of brief sights, the factor of a pencil or the blub- line can be used rather than a ranging rod. The blunders varies inversely with the period of sight. (vii) Other mistakes such as: (a) Mistake in placing the verniers, (b) Mistake in studying the scales and verniers, (c) Mistake in studying incorrect verniers, and (d) Mistake whilst reserving the readings may be averted via way of means of recurring tests and precautions.
Key takeaways:
Non-adjustment of plate degrees: If the plate degrees which aren't perpendicular to the vertical axis, are centered, the vertical axis of the tool isn't always made virtually vertical. As a result, the horizontal circle is willing and the angles are measured in an willing aircraft in place of in a horizontal aircraft
There are numerous strategies of traversing, relying at the units utilized in figuring out the relative guidelines of the traverse lines.
Chain traversing
Chain and compass traversing
Transit kind traversing a)By rapid needle technique b)By dimension of angles among the lines.
Right here are numerous techniques of traversing, relying at the devices utilized in figuring out the relative instructions of the traverse traces. The following are the foremost techniques: Chain traversing Chain and compass traversing Transit kind traversing a)By rapid needle technique b)By dimension of angles among the traces Plane desk traversing Brief descriptions of those traverse surveying techniques are given below. Chain Traversing The technique wherein the complete paintings is performed with chain and tape is known as chain traversing. No perspective dimension is used and the instructions of the traces are constant completely via way of means of linear measurements Angles constant via way of means of linear or tie measurements are called chain angles. The technique is wrong for correct paintings and is usually used if an perspective measuring devices which include a compass, sextant or theodolite is available. Chain and Compass Traversing In chain and compass traversing, the magnetic bearings of the survey traces are measured via way of means of a compass and the lengths of the traces are measured both with a sequence or with a tape. The course of the magnetic meridian is mounted at every traverse station independently. The technique is likewise called a tree or unfastened needle technique.
Traversing via way of means of Fast Needle Method The technique wherein the magnetic bearings of traverse traces are measured via way of means of a theodolite equipped with s compass is known as traversing via way of means of rapid needle technique. The course of the magnetic meridian isn't always mounted at every station however instead, the magnetic bearings of the traces are measured with a reference in order that course of the magnetic meridian mounted at the primary station. There are 3 techniques of looking at the bearings of traces via way of means of rapid needle technique. Direct technique with transiting, Direct technique with out transiting, Back bearing technique. Traversing By Direct Observation Of Angles In this technique, the angles among the traces are without delay measured via way of means of a theodolite and the magnetic bearing of different traces may be calculated on this technique. The angles measured at distinct stations can be both Included Angles and Deflection Angles Traversing via way of means of Included Angle An protected perspective at a station is both of the 2 angles shaped nby survey traces assembly there and those angles have to be measured clockwise. The technique is composed without a doubt in measuring every perspective without delay from a lower back sight at the previous station. The angled will also be measured via way of means of repetition. The angles measured from the lower back station can be indoors or outdoors relying at the course of progress.
The path of development is counter-clockwise and so the angles measured clockwise are the indoors attitude. In Fig(a) the path of development is clockwise and so the angles measured clockwise are the outside attitude. Traverse via way of means of Deflection Angles A deflection attitude is an attitude wherein a survey line makes with the prolongation of the previous line. It is certain as proper (R) or left (L) as it's far measured clockwise or anti-clockwise from the prolongation of the preceding line. This sort of traversing is extra appropriate for the survey of roads, railways, pipe-traces, and so forth wherein the survey traces make small deflection angles. Errors in Traversing The mistakes concerned in closed traversing are kinds: Linear Error and Angular Error The maximum excellent technique of checking the linear measurements is composed in chaining every survey line a 2nd time, ideally withinside the opposite path on extraordinary dates and via way of means of extraordinary parties. The following are tests for the angular paintings: Travers via way of means of protected angles: The sum of measured indoors angles must be same to (2N-4), wherein N=range of facets of the traverse. If the outside angles are measured, their sum must be same to (2N=4)p/2 Travers via way of means of deflection angles: The algebraic sum of the deflection angles must be same to 360°, taking the proper hand and deflection angles as a effective and left-hand attitude as negative. Traversing via way of means of direct statement of bearings: The pressure bearing of the remaining line must be same to its returned bearing ±180° measured from the preliminary station. Checks in Open Traverse No direct tests of angular dimension are available. So oblique tests may be made. As illustrated in the addition to the statement of bearing of AB at station A, bearing of AD also can be measured., if possible. Similarly, at D, the bearing of DA may be measured and test applied. If the 2 bearings range via way of means of 180°, the paintings can be regular as correct.
Another method, which furnishes a test while paintings is plotted is proven as in Fig (b) and includes studying the bearing to any distinguished factor P from every of the consecutive stations. The test-in plotting is composed in shedding the traces AP, BP, CP, and so forth and noting whether or not the traces by skip via one factor.
Key takeaways:
Non-adjustment of plate degrees: If the plate degrees which aren't perpendicular to the vertical axis, are centered, the vertical axis of the tool isn't always made virtually vertical. As a result, the horizontal circle is willing and the angles are measured in an willing aircraft in place of in a horizontal aircraft
The range of a line is its projection at the north-south meridian and is identical to the period of the road instances the cosine of its bearing. The departure of a line is its projection at the east-west meridian and is identical to the period of the road instances the sine of its bearing. The range is the y factor of the road (additionally referred to as northing), and the departure is the x factor of the road (additionally referred to as easting).
The algebraic sum of all latitudes ought to same 0 or the distinction in range among the preliminary and very last manage points The algebraic sum of all departures ought to same 0 or the distinction in departure among the preliminary and very last manage points If the sums of latitudes and departures do now no longer same 0, corrections ought to be made.
Latitude is the north-south element of a line; departure the east-west. North latitudes are positive, South are negative; further East departures are positive, West are negative.
Key takeaways:
The range of a line is its projection at the north-south meridian and is identical to the period of the road instances the cosine of its bearing
A traverse is balanced through making use of corrections to latitudes and departures. This is known as In case of a closed traverse, the algebraic sum of latitudes and departuresbalancing a traverse have to be identical to zero (i.e. L=zero and D=zero).
Adjusting a traverse (additionally referred to as balancing a traverse) is used to dispensed the closure mistakes lower back into the attitude and distance measurements.
Adjusting a traverse (additionally referred to as balancing a traverse) is used to allotted the closure mistakes lower back into the perspective and distance measurements. As with different survey adjustments, the approach used to stability a traverse ought to mirror the anticipated mistakes conduct and be repeatable
This technique is evolved for balancing a traverse wherein angles are measured with a better diploma of precision than the lengths of the sides. It is primarily based totally on the belief that the mistake in departure (or latitude) of a traverse facet is proportional to its departure (or latitude). Thus, in keeping with the transit rule, the corrections to the departure (or latitude) of a traverse facet
Key takeaways:
A traverse is balanced through making use of corrections to latitudes and departures. This is known as In case of a closed traverse, the algebraic sum of latitudes and departuresbalancing a traverse have to be identical to zero (i.e. L=zero and D=zero).
References:
1. Duggal, S.K. Surveying Vol. I and II, Tata McGraw Hill, 2004.
2. Punmia, B.C. Surveying Vol. I and II, Standard Publishers, 1994.
3. Arora, K. R. Surveying Vol. I and II, Standard Book House, 1996
4 N.N Basak. Surveying and levelling
