Module 1 tacheometry
7 likes2,566 views
The document discusses tacheometric surveying, outlining its advantages like reduced time and applicability in difficult terrains, as well as disadvantages regarding accuracy requirements. It explains various methods such as the stadia and tangential methods, and introduces devices like electronic distance measurement instruments and total stations, highlighting their benefits in terms of speed and precision. The document also covers the use, functionality, and advantages of subtense bars in surveying.
![ELECTRONIC DISTANCE MEASURMENTS [EDM]
• Electronic distance measuring instrument is a surveying instrument for measuring
distance electronically between two points through electromagnetic waves.
• The method of direct distance measurement cannot be implemented in difficult
terrains.
• When large amount of variation in the terrain or large obstructions exist, this
method is avoided.
• As an alternative to this optical distance measurement method was developed.
Still it gained a disadvantage of limited range of measurement.
• It is limited to 15 to 150m with an accuracy of 1 in 1000 to 1 in 10000. Above all
we have EDM with an accuracy of 1 in 105, having a distance range of 100km.
Prepared By-
Prof. Basweshwar S. J.](https://image.slidesharecdn.com/module-1tacheometry-200109060000/85/Module-1-tacheometry-16-320.jpg)
Module 1 tacheometry
- 1. Tachometric surveying Prepared By- Prof. Basweshwar S. J.
- 2. Prepared By- Prof. Basweshwar S. J.
- 3. Advantages of Tacheometric surveying It eliminates use of chain and tape. . We can do survey in area like Hill and mountain where it is very difficult to do survey by other methods. If we not need very high standards and accuracy then this is right method. It require low amount of time compare to other ways of surveying. Because Tacheometry is indirect method that we do not require some instrument that is necessary in plan table surveying or in theodolite surveying. Prepared By- Prof. Basweshwar S. J.
- 4. Disadvantages of Tacheometric surveying Major disadvantage of tacheometric surveying is that, it is not used where higher accuracy is required. Prepared By- Prof. Basweshwar S. J.
- 5. Applications In rough country, both horizontal and vertical measurements are tedious and chaining is in accurate, slow and difficult. when obstacles such as steep and broken ground, stretches of water. In locating contours and filling in detail in a topographic survey, this method is usually the quickest & best. When area to be surveyed is very large and accuracy required is less. Prepared By- Prof. Basweshwar S. J.
- 6. Applications Preparation of topographic maps which require both horizontal distances and elevations. Survey work in difficult terrain where direct methods are inconvenient. Filling details in a traverse. location surveys for highways, railways, canals, etc. hydrographic surveys. Prepared By- Prof. Basweshwar S. J.
- 7. Prepared By- Prof. Basweshwar S. J.
- 8. Prepared By- Prof. Basweshwar S. J.
- 9. Stadia method • It is the most prevalent method for tacheometric surveying. • In this method, the telescope of the theodolite is equipped with two additional cross hairs, one above and the other below the main horizontal hair at equal distance. • These additional cross hairs are known as stadia hairs. Tangential Method • The tangential method of tacheometry is being used when stadia hairs are not present in the diaphragm of the instrument. • In this method, the staff sighted is fitted with two big targets (or vanes) spaced at a fixed vertical distances. • Vertical angles corresponding to the vanes, say q1 and q2 are measured. • The horizontal distance, say D and vertical intercept, say V are computed from the values s (pre-defined / known) q1 and q2 . • This method is less accurate than the stadia method.Prepared By- Prof. Basweshwar S. J.
- 10. Fixed Hair Method: In the fixed hair method the cross hairs of the diaphragm are kept at a constant distance apart and the staff intercept varies with the horizontal and vertical position of the staff with respect to the Theodolite. Movable Hair Method: In this method the staff intercept between the lower hair and the upper hair is kept constant by moving the horizontal cross hairs in the vertical plane. Prepared By- Prof. Basweshwar S. J.
- 11. 2. Additive constant B=(f+d) where, f=focal length of the lens d= horizontal distance between instrument axis to optical centre of a lens The value of additive constant. varies from 0.15 m to 0.60 m. Prepared By- Prof. Basweshwar S. J.
- 12. In tachometric surveying, instrument used is known as a tachometer. With the help of a tachometer observations (stadia readings and vertical angles) are taken and horizontal and vertical distances are determined by using formulae. Before doing calculations we should known the values of two constants for a tachometer to be used for survey work. Generally their values are mentioned in the catalogue supplied by the manufacturer. Also the constants may be determined by: 1.Laboratory measurement 2. Field measurementPrepared By- Prof. Basweshwar S. J.
- 13. Anallatic lens It is an additional lens generally provided in the external focusing tachometer between object glass & eyepiece Advantages of anallatic lens: 1) For calculation of horizontal & vertical distances constant (f+c)=0, if tacheometer is provided with anallatic lens. 2) Calculation becomes simple. Disadvantages of anallatic lens: 1. The anallatic lens absorbs some of the incident light which consequently results in reduction of the brightness of the image. 2. It also adds to the initial cost of the instrument because of one extra lens. Prepared By- Prof. Basweshwar S. J.
- 14. Auto reduction Tachometer Prepared By- Prof. Basweshwar S. J.
- 15. FIELD WORK • Set up the instrument. • Set the vernier of the vertical circle to zero. • With the altitude level at the center of its run, measure the height of the instrument with a measuring tape accurately. • Orient the instrument. • Hold the staff on the benchmark and take the bearing, read the vertical angle and the top, bottom, and axial hair readings. • If any benchmark is not nearby the area of traversing, Fly level may be carried out. • After all the representative points are located from the first station, take a foresight at the second station and note down the bearings. • Vertical angle and the staff readings corresponding to the top, bottom and the axial hairs. • As each station is sighted twice two Values for the distances and elevations of the stations are obtained which should be within the permissible limits; otherwise, the work should be repeated. Prepared By- Prof. Basweshwar S. J.
- 16. ELECTRONIC DISTANCE MEASURMENTS [EDM] • Electronic distance measuring instrument is a surveying instrument for measuring distance electronically between two points through electromagnetic waves. • The method of direct distance measurement cannot be implemented in difficult terrains. • When large amount of variation in the terrain or large obstructions exist, this method is avoided. • As an alternative to this optical distance measurement method was developed. Still it gained a disadvantage of limited range of measurement. • It is limited to 15 to 150m with an accuracy of 1 in 1000 to 1 in 10000. Above all we have EDM with an accuracy of 1 in 105, having a distance range of 100km. Prepared By- Prof. Basweshwar S. J.
- 17. Sun light or artificially generated electromagnetic wave consists of waves of different lengths. The spectrum of an electromagnetic wave is as shown below: Prepared By- Prof. Basweshwar S. J.
- 18. Types of Electronic Distance Measurement Instrument Microwave instruments Infrared wave instruments Light wave instruments. These instruments make use of microwaves. In this instrument amplitude modulated infrared waves are used. These instruments rely on propagation of modulated light waves. The instrument needs only 12 to 24 V batteries. Prism reflectors are used at the end of line to be measured. Light waves are most suited way in this instrument. They are light and highly portable. Tellurometers can be used in day as well as in night. These instruments are light and economical and can be mounted on theodolite. These instruments are also very useful for civil engineering projects. The range of these instruments is up to 100 km. With these instruments accuracy achieved is ± 10 mm. The range of these instruments is up to 3 km. During night its range is up to 2.5 km while in day its range is up to 3 km. Accuracy of these instruments varies from 0.5 mm to 5 mm/km distance. Prepared By- Prof. Basweshwar S. J.
- 19. From the transit time and known velocity, the distance can be easily measured. Now to solve the problem arise due to difficulty in starting the timer at B, a reflector can be placed as shown below instead of a receiver at B. Fig. Transit measurement arrangement with the help of a EDM and a reflector Prepared By- Prof. Basweshwar S. J.
- 20. ERRORS in Electronic Distance Measurement Personal Errors Instrumental Errors Natural Errors Inaccuracy in initial setups of EDMs and the reflectors over the preferred stations Calibration errors Atmospheric variations in temperature, pressure as well as humidity. Instrument and reflector measurements going wrong Chances of getting maladjusted time to time generating frequent errors. Micro wave EDM instruments are more susceptible to these. Atmospheric pressures and temperature determination errors Errors shown by the reflectors. Multiple refraction of the signals. • The advantage of using EDM instruments is the speed and accuracy in measurement. • Several obstacles to chaining are automatically overcome when these instruments are used.Prepared By- Prof. Basweshwar S. J.
- 21. STUDY AND USE OF TOTAL STATION • Total station is a surveying equipment combination of Electromagnetic Distance Measuring Instrument and electronic theodolite. • It is also integrated with microprocessor, electronic data collector and storage system. • The instrument can be used to measure horizontal and vertical angles as well as sloping distance of object to the instrument. Capability of a Total Station Microprocessor unit in total station processes the data collected to compute: • Average of multiple angles measured. • Average of multiple distance measured. • Horizontal distance. • Distance between any two points. • Elevation of objects and • All the three coordinates of the observed points. Prepared By- Prof. Basweshwar S. J.
- 22. Prepared By- Prof. Basweshwar S. J.
- 23. Important Operations of Total Station Distance Measurement- range varies from 2.8 km to 4.2 km. Angle Measurements- angle measurement varies from 2 to 6 seconds. Data Processing- computes the horizontal distance and X, Y, Z coordinates. Display- capable of displaying horizontal distance, vertical distance, horizontal and vertical angles, difference in elevations of two observed points Electronic Book- capacity of electronic note book varies from 2000 points to 4000 points data.Prepared By- Prof. Basweshwar S. J.
- 24. Prepared By- Prof. Basweshwar S. J.
- 25. Advantages of Using Total Stations The following are some of the major advantages of using total station over the conventional surveying instruments: 1.Field work is carried out very fast. 2.Accuracy of measurement is high. 3.Manual errors involved in reading and recording are eliminated. 4.Calculation of coordinates is very fast and accurate. 5.Corrections for temperature and pressure are automatically made. 6.Computers can be employed for map making and plotting contour and cross- sections. 7.Contour intervals and scales can be changed in no time.Prepared By- Prof. Basweshwar S. J.
- 26. SUBTENSE BAR Prepared By- Prof. Basweshwar S. J.
- 27. The subtense bar is an instrument used for measuring the horizontal distance between the instrument station and a station where the subtense bar is to be set up. Substense method is an indirect method of distance determination. This method essentially consists of measuring the angle subtended by two ends of a horizontal rod of fixed length, called a subtense bar. In this method a staff or target rod is not necessary, and the theodolite required is also of the ordinary transit type. Prepared By- Prof. Basweshwar S. J.