# Definition of Tacheometric Surveying
Tacheometric surveying is a method of angular surveying in which a tachometer is used to measure the horizontal and vertical distance between two points, eliminating the need for chain surveying.
# Advantages of Tacheometric Surveying
Tacheometric surveying is faster and more convenient than chain or tape surveying, particularly in challenging terrains such as broken ground, ravines, swamps, and water bodies. It also boasts an accuracy of 1/1000 to 1/10000.
Principle of Tacheometric Surveying
The formula for the horizontal distance is determined using:
H= K*s* cos ² θ
Note: The additive constant is 0.00, and the multiplying constant is 100.00.
The formula for the vertical distance for the same tacheometer is:
Where,
s= staff intercept = Top Reading – Bottom Reading
K= Multiplying Constant (generally taken as 100
θ = Vertical angle on the theodolite
R.L. of the point = R.L. of the instrument + (H.I. of the instrument − R) × Constant.
R.L of Point = R.L of Instrument Station + H.I ± V-R
Procedure for Tacheometric Surveying
1. Setup and Level the Instrument:
This step involves setting up the instrument above the specified station and precisely leveling it with reference to the altitude level. To do this, set the vertical circle’s vernier to zero and use a measuring tape to precisely measure the instrument’s height. Alternatively, the height can be found by keeping the stadia rod first before the telescope and reading through the object-glass.
2. Orient the Instrument:
When orienting the instrument, the magnetic meridian or the real meridian can be used as the reference meridian. If using the magnetic meridian, set one of the verniers to zero and rotate the telescope around the vertical axis, relaxing the bottom clamp until the compass needle points north. If using the real meridian, set the vernier to the bearing of a reference point or another station of the traverse and rotate the telescope about the outer axis until the station or reference object is bisected.
3. Take Measurements:
While holding the staff on the benchmark, take the bearing, the vertical angle, and the top, bottom, and axial hair readings. If there is no local benchmark, fly level from the nearest accessible Bench Mark (B.M.) and a temporary B.M. may be constructed near the region.
4. Change Stations:
Change the station of the instrument to the second and set up, center, and level the instrument before measuring its height. Take a back sight to the first station and note the bearings, the vertical angle, and the staff readings for the top, bottom, and axial hairs.
5. Check Values:
Once each station is sighted twice, two values for the station’s distances and altitudes are produced, which must be within the legal limits; otherwise, the operation must be redone.
Methods of Tacheometric Surveying
Tacheometric surveying is further classified into two methods, namely, the slope tacheometry and the trigonometric tacheometry. In slope tacheometry, the horizontal distance is calculated by measuring the angles horizontally and vertically, while in trigonometric tacheometry, the horizontal distance is calculated by measuring the angles by trigonometric functions.
1. Stadia Method of Tacheometry
# Advantages of Tacheometric Surveying
Tacheometric surveying is faster and more convenient than chain or tape surveying, particularly in challenging terrains such as broken ground, ravines, swamps, and water bodies. It also boasts an accuracy of 1/1000 to 1/10000.
# Principle of Tacheometric Surveying
The principle of tacheometric surveying is based on the property of an isosceles triangle, which states that the ratio of the distance of the base from the apex and the length of the base is always constant. This allows for the calculation of the reduced level of the instrument station (R.L.), the height of the instrument (H.I.), central wire reading (R), and the R.L. of any point under observation.
# Types of Tacheometric Surveying
The stadia technique of tacheometry is a popular method for calculating horizontal distance and vertical elevation, which only requires one observation from the instrument
A. Fixed Hair Method
The other method is the angle-measuring technique. This method is based on the concept of trigonometry and the measure of the angle between the two points. It does not require the use of a staff.
# Definition of Tacheometric Surveying
Tacheometric surveying is a method of angular surveying in which a tachometer is used to determine the horizontal and vertical distance between two points, eliminating the need for chain surveying.
# Advantages of Tacheometric Surveying
Tacheometric surveying is faster and more convenient than chain or tape surveying, particularly in challenging terrains such as broken ground, ravines, swamps, and water bodies. It also boasts an accuracy of 1/1000 to 1/10000.
# Principle of Tacheometric Surveying
The principle of tacheometric surveying is based on the property of an isosceles triangle, which states that the ratio of the distance of the base from the apex and the length of the base is always constant. This allows for the calculation of the reduced level of the instrument station (R.L.), the height of the instrument (H.I.), central wire reading (R), and the R.L. of any point under observation.
# Types
B. Movable Hair Method
1. Setup and Level the Instrument:
This step involves setting up the instrument above the specified station and precisely leveling it with reference to the altitude level. To do this, set the vertical circle’s vernier to zero and use a measuring tape to precisely measure the instrument’s height. Alternatively, the height can be found by keeping the stadia rod first before the telescope and reading through the object-glass.
2. Orient the Instrument:
When orienting the instrument, the magnetic meridian or the real meridian can be used as the reference meridian. If using the magnetic meridian, set one of the verniers to zero and rotate the telescope around the vertical axis, relaxing the bottom clamp until the compass needle points north. If using the real meridian, set the vernier to the bearing of a reference point or another station of the traverse and rotate the telescope about the outer axis until the station or reference object is bisected.
3. Take Measurements:
While holding the staff on the benchmark, take the bearing, the vertical angle, and the top, bottom, and axial hair readings. If there is no local benchmark, fly level from the nearest accessible Bench Mark (B.M.) and a temporary B.M. may be constructed near the region.
4. Change Stations:
Change the station of the instrument to the second and set up, center, and level the instrument before measuring its height. Take a back sight to the first station and note the bearings, the vertical angle, and the staff readings for the top, bottom, and axial hairs.
5. Check Values:
Once each station is sighted twice, two values for the station’s distances and altitudes are produced, which must be within the legal limits; otherwise, the operation must be redone.
6. Movable Hair Method:
In contrast to the stadia hair technique, the telescope connected to the instrument in the movable hair method comprises moveable cross-hairs. The center hair can also be used to fix the moveable cross-hairs. The stadia interval is customizable in this manner for different staff positions. The horizontal distance is then calculated. The gadget is used with two fixed-distance targets.
2. Tangential Method of Tacheometric Surveying
1. Setup and Level the Instrument:
This step involves setting up the instrument above the specified station and precisely leveling it with reference to the altitude level. To do this, set the vertical circle’s vernier to zero and use a measuring tape to precisely measure the instrument’s height. Alternatively, the height can be found by keeping the stadia rod first before the telescope and reading through the object-glass.
2. Orient the Instrument:
When orienting the instrument, the magnetic meridian or the real meridian can be used as the reference meridian. If using the magnetic meridian, set one of the verniers to zero and rotate the telescope around the vertical axis, relaxing the bottom clamp until the compass needle points north. If using the real meridian, set the vernier to the bearing of a reference point or another station of the traverse and rotate the telescope about the outer axis until the station or reference object is bisected.
3. Take Measurements:
While holding the staff on the benchmark, take the bearing, the vertical angle, and the top, bottom, and axial hair readings. If there is no local benchmark, fly level from the nearest accessible Bench Mark (B.M.) and a temporary B.M. may be constructed near the region.
4. Change Stations:
Change the station of the instrument to the second and set up, center, and level the instrument before measuring its height. Take a back sight to the first station and note the bearings, the vertical angle, and the staff readings for the top, bottom, and axial hairs.
5. Check Values:
Once each station is sighted twice, two values for the station’s distances and altitudes are produced, which must be within the legal limits; otherwise, the operation must be redone.
Errors and Precautions in Tacheometric Surveying
The commonly occurring errors in the tacheometric survey are due to the following reasons.
1. Instrumental Errors
1. Setup and Level the Instrument:
This step involves setting up the instrument above the specified station and precisely leveling it with reference to the altitude level. To do this, set the vertical circle’s vernier to zero and use a measuring tape to precisely measure the instrument’s height. Alternatively, the height can be found by keeping the stadia rod first before the telescope and reading through the object-glass.
2. Orient the Instrument:
When orienting the instrument, the magnetic meridian or the real meridian can be used as the reference meridian. If using the magnetic meridian, set one of the verniers to zero and rotate the telescope around the vertical axis, relaxing the bottom clamp until the compass needle points north. If using the real meridian, set the vernier to the bearing of a reference point or another station of the traverse and rotate the telescope about the outer axis until the station or reference object is bisected.
3. Take Measurements:
While holding the staff on the benchmark, take the bearing, the vertical angle, and the top, bottom, and axial hair readings. If there is no local benchmark, fly level from the nearest accessible Bench Mark (B.M.) and a temporary B.M. may be constructed near the region.
4. Change Stations:
Change the station of the instrument to the second and set up, center, and level the instrument before measuring its height. Take a back sight to the first station and note the bearings, the vertical angle, and the staff readings for the top, bottom, and axial hairs.
5. Check Values:
Once each station is sighted twice, two values for the station’s distances and altitudes are produced, which must be within the legal limits; otherwise, the operation must be redone.
6. Instrumental Mistakes:
Instrumental mistakes can occur as a result of faulty permanent modifications in the instrument or inaccurate graduations on the stadia rod.
2. Manipulation and Sighting Error
Affect of Manipulation and Sight on Accuracy
The accuracy of a survey can be significantly impacted by incorrect manipulation and sight. This is due to the surveyor’s efficiency and expertise in carrying out the survey, as well as potential errors in instrument centering, leveling, and stadia readings.
Impact of Surveyor’s Efficiency
The surveyor’s skill in manipulating and sighting can greatly affect the accuracy of the survey. If the surveyor is not sufficiently experienced or efficient, errors may occur in instrument centering, leveling, and stadia readings, leading to inaccurate survey results.
Potential Errors in Instrument Centering, Leveling, and Stadia Readings
Incorrect instrument centering, leveling, and stadia readings can lead to inaccuracies in the survey. These errors can be caused by the surveyor’s inefficiency or lack of expertise, as well as by faulty instrument centering and leveling.
3. Natural Causes
Factors Affecting Survey Accuracy
The accuracy of a survey is largely determined by the surveyor’s efficiency and expertise in manipulating and sighting, as well as the potential errors that may occur in instrument centering, leveling, and stadia readings.
Impact of Surveyor’s Skill
The surveyor’s skill in manipulating and sighting is a critical factor in the accuracy of the survey. Poor manipulation and sighting can lead to errors in instrument centering, leveling, and stadia readings, resulting in inaccurate survey results.
Potential Sources of Error
Instrument accuracy can be compromised by a number of factors, including wind, asymmetrical expansion of instrument components, visibility, and unequal refraction. Of these, unequal refraction is the most significant.
Advantages of Tacheometric Surveying
The following are some of the advantages of tacheometric surveying:
- The speed with which such a survey is conducted is quick.
- The procedure does away with the usage of tapes and chains. As a result, it is less time-consuming.
- It is a low-cost way of surveying.
- The precision of this approach is also good enough for the compilation of topographic maps, hydrological surveys, and cross-checking measurements from other methods, among other things.
FAQs
What is a tacheometric survey?
Factors Affecting Survey Accuracy
The accuracy of a survey is largely determined by the surveyor’s expertise and skill in manipulating and sighting, as well as potential errors in instrument centering, leveling, and stadia readings.
Surveyor’s Expertise and Skill
The surveyor’s expertise and skill in manipulating and sighting are essential for obtaining accurate survey results. Poor manipulation and sighting can lead to mistakes in instrument centering, leveling, and stadia readings, resulting in inaccurate survey results.
Sources of Error in Tacheometric Surveying
Tacheometric surveying is a method of angular surveying in which a tachometer is used to determine the horizontal and vertical distance between two points, eliminating the need for chain surveying to measure horizontal distance. Potential sources of errors in tacheometric surveying include wind, asymmetrical expansion of instrument components, visibility, and unequal refraction.
What is the principle of tacheometric surveying?
Factors Affecting Survey Accuracy
The accuracy of a survey is determined by the surveyor’s efficiency and expertise in manipulating and sighting, as well as potential errors in instrument centering, leveling, and stadia readings.
Surveyor’s Skill and Expertise
The surveyor’s expertise and skill in manipulating and sighting is essential for obtaining accurate survey results. Poor manipulation and sighting can lead to mistakes in instrument centering, leveling, and stadia readings, resulting in inaccurate survey results.
Principles of Tacheometric Surveying
Tacheometric surveying is a method of angular surveying in which a tachometer is used to determine the horizontal and vertical distance between two points. This eliminates the need for chain surveying to measure horizontal distance and relies on the principle of an isosceles triangle, in which the ratio of the distance of the base from the apex and the length of the base is always constant.
What are the common errors in tacheometric surveys?
The commonly occurring errors in the tacheometric survey are due to the following reasons.
1. Instrumental Errors
2. Manipulation and Sighting Error
3. Natural Causes
What are the advantages of tacheometric surveying?
Factors Affecting Survey Accuracy
The accuracy of a survey is determined by the surveyor’s efficiency and expertise in manipulating and sighting, as well as potential errors in instrument centering, leveling, and stadia readings.
Surveyor’s Skill and Expertise
The surveyor’s expertise and skill in manipulating and sighting is essential for obtaining accurate survey results. Poor manipulation and sighting can lead to mistakes in instrument centering, leveling, and stadia readings, resulting in inaccurate survey results.
Advantages of Tacheometric Surveying
Tacheometric surveying offers several advantages that can make it an ideal surveying method for certain projects. These include the speed of surveying, cost-effectiveness, and good precision.