Last updated on September 12th, 2023 at 12:13 pm
Theodolite survey procedure is the most accurate instrument theodolite used in the measurement of horizontal and vertical angles.
It consists of a telescope to see distant objects. The telescope has two distinct motions, one in the horizontal plane and the other in the vertical plane.
The horizontal angle is measured on the graduated horizontal circle by means of two verniers.
It can also be used for various other purposes such as laying of horizontal angles, locating points on a line, prolonging theodolite survey procedure lines, establishing grids, determining differences in elevation, etc.
- Foot screws (leveling screw)
- Plumb bob
- Lower plate
- Upper plate
- Spirit level
- Vertical circle
- Vertical circle clamping screw
- Lower plate clamping screw
- Lower plate tangent screw
- Upper plate clamping screw
- Upper plate tangent screw
USE OF THEODOLITE SURVEY?
- For demarcation of plot boundaries and existing structures at any stage of work.
- For line out of the compound wall, boundary wall garden wall, electric pole, etc. to maintain a straight line throughout.
- For taking a straight line where considerable obstructions of hutments, soil heaps, trees, etc. are observed.
- For line-out in the deep basement where the plumb line is not possible by means of the plumb bob.
- For line-out and building settings.
- Setting out a series of buildings in project premises.
- Setting out centers of columns from the face of buildings.
- For maintaining the vertical face of the building, if the height is considerably more.
HOW TO USE THEODOLITE?
- First, get acquainted with all the parts of the theodolite.
- Know and follow all the procedures of adjustments and operations.
- Plan the total work in advance for ease of all activities, minimum operation, and more accuracy in work.
- Do not overtighten any screws.
ADJUSTMENTS OF THE THEODOLITE?
There are two kinds of adjustment in theodolite.
- Temporary adjustment-> To be done by an engineer or user.
- Permanent adjustment – To be done by a technician mechanic.
1. TEMPORARY ADJUSTMENT
Temporary adjustments are those which have to Be made every time the instrument is set up. Before taking any readings. Temporary adjustments of the theodolite are
- Setting up the theodolite.
- Theodolite Levelling the instrument.
- Focusing the eyepiece and object glass.
2. PERMANENT ADJUSTMENT
Permanent adjustments are those which establish the fixed relationships between the fundamental lines of the instrument.
When the permanent adjustments are adjusted, they remain for a long period.
Permanent adjustments are
- The vertical axis
- The axis of the plane level
- The line of collimation or the line of sight
- The horizontal axis
- The bubble line or the altitude level
MEASUREMENT OF VERTICAL AND HORIZONTAL ANGLE USING THEODOLITE
SETTING UP OF THEODOLITE?
- Make the station by wire nail, M.S. rod, oil paint on the pillar, etc.
- Place the tripod over the station, approximately by means of suspending the plumb bob.
- Fix the theodolite over the tripod.
- Fix the plumb bob to the instrument.
- Release the bottom clamping screw smoothly and ensure that the theodolite rests on the bottom plate and is not eccentric in the vertical plumb.
- Adjust the tripod by moving each leg along the radius as well as the circumference, so as to bring the plumb bob exactly over the station mark and approximately level the instrument with the help of the built-in spirit level.
- While moving the legs ensure that the plate level should not be seriously affected.
- Theodolite survey leveling the Instrument by means of tripod legs, as explained Initially, saves time.
- Once the plumb bob is exactly on the center of the station, do the leveling of the instrument, like the dumpy level explained earlier.
- After satisfactory leveling of the instrument. see from the bottom eye telescope whether the Fig. No. 17.3 Setting up the theodolite. center of the station is matching exactly to the cross-hair of the bottom telescope.
- If the center of the station does not match the cross-hair, loosen the bottom clamping and release the instrument to slide right/left/along the circumference, and move accordingly to match the crosshair exactly with the center of the station.
- Tighten the bottom clamping and check the firmness of the instrument.
- Check the leveling of the instrument again and re-confirm the centering of the station.
- Make the cross-hair distinct by focusing on the piece.
- Set the bottom and top vernier plates namely A and B to zero.
NOW YOUR THEODOLITE IS READY FOR WORK
PROCEDURE FOR MEASURING THE HORIZONTAL ANGLE AND PROJECTING THE LINE IN THEODOLITE SURVEY?
- Direct the telescope towards the object and using the eyepiece, bring the image of the object in line with the vertical hairs of the diaphragm.
- For the minute horizontal movement, use a tangent screw and set the line accordingly.
- Look at the movement vertically by using the vertical clamping screw.
- Now, if the line is to be projected for further length, release the top vertical clamping screw and move the telescope vertically as required and take the intermediate points. It can also be moved through 180 degrees, to bisect the point located on another side of the instrument.
- For taking a right angle to the line, loosen the top vernier screw, and move the theodolite through 9 degrees by visual observation of the vernier scale. For fine adjustment use the tangent screw.
- Set the line by taking intermediate points. This line is at the right angle to the parent line. Also, the telescope can be moved through 180 degrees for bisecting the points which are on the other side of the instrument, if required.
- This way, by releasing the top plate screw, rotate the telescope horizontally and take any horizontal angle at any point.
This the procedure of setting of lines should be followed it all required points. If any error is found in closing f traverse then re-checking should be done, the error is considerable. After completing the traverse, the error should not exceed 05 mm at any point.
After use keeps the theodolite in the box with due care to avoid damage.
HOW TO MEASUREMENTS THE VERTICAL ANGLE IN THEODOLITE SURVEY?
A vertical angle is an angle between the inclined line of sight and the horizontal plane. Since the vertical angle to a point is measured from the horizontal plane passing through the horizontal axis of the instrument, it may be an angle of elevation or an angle of depression according to the point as above or below the horizontal plane.
1. TO MEASUREMENTS THE VERTICAL ANGLE OF AN OBJECT ‘A’ AT A STATION ‘0’
- Set up the instrument accurately with reference to the altitude bubble.
- Set the zero of vertical over ‘0’ and level it vernier exactly to the Zero of the vertical circle by means of the vertical circle clamp and tangent screw.
- Bring the bubble of altitude level to the center of its Fun, by means of the clip screws. The line of Collimation Is thus made perfectly horizontal, while the vernier reads zero.
- Loosen the vertical circle clamp and direct the. Telescope towards object A and when it Is approximately insight, clamp the vertical circle and bisect ‘An exactly by turning the tangent screw.
- Read both the verniers. The mean of the two readings gives the value of the required angle.
- Change the face of the instrument and repeat The process. The mean of the two vernier readings gives the second value of the required angle.
- Bisect ‘A’ as before and note the reading on the vertical circle.
- Similarly, bisect B.and note the reading on the vertical circle
- The sum or difference of these readings will give the value of the angle between A and B.
DEMARCATION SURVEY BY USING THEODOLITE?
Demarcation of any area can be done by theodolite which could be plotted on drawing at actual. The demarcation can be done by plane table or theodolite.
Demarcation by theodolite is the most accurate method if the area is not large, but this should be done very precisely.
The following procedure should be followed for demarcation of any plot, of any size by using a theodolite.
The following procedure should be followed for demarcation of any plot, of any size by using a theodolite.
THEODOLITE SURVEY CALCULATION
Let the plot be “PORSTUV” to be demarcated and plotted on drawing.
Set the theodolite as per the given procedure on any point ‘A’, marked with M.S. pegs or marking stones. Select the point ‘A’ near any corner of plot (P) from where maximum boundaries can be measured with one tape measurement. Bisect any point D’ to the other end (QR).
Fix the point ‘D’ to the other end of plot boundary (OR) and, within the tape measurement of the boundary (PQ).
Clamp the bottom screw and take intermediate points like AD1, B. AD2, etc. at any distances suitable to take the nearest ordinates on boundary PQ.
Point ‘B’ and ‘C’ on line AD should be selected in such a way that perpendicular lines CC3, BB7 should pass nearly along the boundaries of a plot which will be suitable to take distances on boundaries.
Points B and C should be kept absolutely undisturbed where theodolite is to be shifted.
Turn the theodolite through 90° and take point E on boundary UV. Take intermediate points AE1, AE2.
Shift and fix the theodolite on point ‘B’.
Set the bottom and top’ vernier scale to zero and clamp top plate screw.
Bisect point ‘A’, clamp bottom plate screw. Bisect the point correctly by a tangent screw.
Checkpoint ‘D’ by transiting the telescope.
Release the top plate screw and turn the telescope by 90 degrees and mark point B7 on the boundary of the plot UV.
Take intermediate points (B1, B2, B3) per the requirement.
Shift and set the theodolite on point ‘C’ and repeat all the procedures the same as for point ‘B’.
Now measure the distances between each point on the ground, on theodolite lines AD, AE, BB7, CC3, AE2 – QR2, and note down on paper.
Mark the points P1, P2, P3 along the boundary of the plot (at random).
Measure the distance of each of the above etc.)points from at least two points of reference lines (AD. BB7. CC3 etc.), so as to locate and draw the exact point on the drawing e.g. point P1 is located by measuring the distance AP1 and AD1.and P1 can be fixed on drawing with the help of compass with the ordinates AP1 and AD1 – PI.
All the distances of the permanent structures, like poles, and trees. (if any), from the baseline and second line should be noted for plotting them on layout drawings.
Keep all the reference points unchanged, till final plotting and checking.
Now plotting on a drawing sheet can be done with a suitable scale.
|Demarcation using theodolite, theodolite survey calculation|
VERY IMPORTANT NOTES
Actual demarcation is required before starting the execution of any new project. Initially. the project layout is prepared by the Architect with the help of the city survey demarcation.
It may differ because of encroachments by adjacent land Owners, existing structures, a new development in the property like a well, electric pole, etc.
Give one copy of the actual demarcation drawing to the Architect, let him mark all the building’s layout on this drawing so that any obstruction in the planned buildings can be understood.
An actual setback can also be checked. obstructions, the layout of the buildings can be modified in the initial stages, before starting In the case of the construction work.
The actual area in possession can also be checked and compared with the area given by the city survey office.
Sometimes, the entire layout has to be changed due to unavoidable changes in the existing plot.
PRECAUTIONARY MEASURES WHILE CARRYING OUT THE THEODOLITE SURVEY
- To begin with, check the theodolite for its permanent adjustments.
- In case of important work like building settings, the stations should be marked with pegs or wire nails.
- Never use steel bars, for important work while locating the stations. Always maintain the rigidity of the peg (station).
- As the thickness of the peg is more, mark a center on it by using oil paint in the case of a metal peg and if a wooden peg is used, insert a pin as the center in the peg.
- Carry out the leveling of the theodolite carefully.
- Maximum adjustments to match the center of the peg and the center of the theodolite should be done with the help of leg adjustments.
- For very fine adjustment of bisecting the exact centers of the intermediate pegs, use the tangent screw.
- Leveling should be perfect from the beginning of the survey. The bubble of the spirit level should always remain in the center for all the positions when rotated in 360 degrees.
- After every reading, check the level of the instrument.
- Do not over-tighten any screws while using the theodolite.
- Do not allow children or passers-by near the instrument.
- The movement of the plumb bob should be free. The ring to which the plumb bob is fixed should have free movement.
- Avoid any theodolite work in heavy winds and sunlight, due to the possibility of variations in the readings.
- While taking the reading on the vernier scale, the eye should be perfectly vertical to the eyepiece of the vernier scale, for an accurate reading.
- Use the same eye during the theodolite survey for taking readings.
- If there is more than one person for carrying out the theodolite survey procedure work, the readings should be taken by a single person throughout the work.
- Always complete the traverse to ensure the correctness of the day’s work.
- Always use steel tape for the measurements of different distances. Do not use metallic tape.
- The string of the plumb bob should be as fine as possible and the point of the plumb bob should be as sharp as possible.
- Always cover the theodolite with a light cloth when not in use, during the theodolite survey.
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