UNIT - 11. What are the different systems of tacheometric survey? Primarily there are tacheometric systems, viz, The Stadia System and the Tangential System.

In the Stadia System the diaphragm of the tacheometer is provided with two stadia hairs (upper and lower ones). There are two kinds of stadia systems. viz., Fixed-hair method and Movable-hair method.

In the Tangential System the diaphragm of the tacheometer is not provided with stadia hairs. Only the single horizontal hair is used to take the reading.

2. What are the three types of telescopes used in stadia surveying? (A.U. Nov/Dec 2009)

The three types of telescopes used in tacheometer Surveying are:

(i) external-focussing telescope(ii) external-focussing anallatic telescope(iii) internal-focussing telescope

The first type is known as stadia theodolite and the Second one is known as tacheometer3. What is an anallactic lens? Anallactic lens is an additional convex lens mounted in external focusing telescope in between the object glass and diaphragm ‘This arrangement is made to reduce the additive constants to zero. This arrangement simplifies the mathematical calculations and only multiplying constant is present. The distances are directly obtained by multiplying the difference of stadia hair readings by 100.

4. List the characteristics should a tacheometer have.A tacheometer should have the following characteristics:

The telescope should be with a magnification of 20 to 30 diameters. For a bright image, the aperture of the objective should be of 35 to 45 mm

diameter. An anallactic lens should be fitted with the telescope such that the

multiplying constant f / i is 100 and the additive constant ( f +d ) is zero. In order to obtain a clear staff reading from a long distance the eye-piece

should be of greater magnifying power.5. Explain fixed-hair stadia method.In this type of method the distance between the stadia hairs is fixed and thus the method is known as fixed-hair method. When a staff is viewed through the telescope. the upper and lower stadia intercept and a certain portion of the staff is seen. The staff intercept varies with the distance between the instrument and staff

position. The distance between the station and the staff is obtained by multiplying the staff intercept by the stadia constant.

6. Differentiate the principles of stadia and subtense methods.As per the stadia principle, whatever may be the distance between the staff and the tacheometer, the tacheometer angle is always constant for a given telescope. The staff intercept varies with the distance between the staff and the instrument which forms the base of stadia measurement. The principle of subtense method is just the reverse of the stadia principle. Here the staff intercept forms the fixed base and the tacheometric angle changes according with the staff position.

7. List the merits and demerits of movable-hair method in tacheometric survey. (AU. Nov-Dec 2008)

Merits

Movable-hair method is more accurate. Long distances can be taken with greater accuracy than in stadia method.

Demerits

Lacks speed in the field. Variables m and i should be measured accurately. Because of these limitations this method is almost obsolete.

8. Explain the use of subtense bar in surveying. The subtense bar is an instrument used for measuring the horizontal distance between the instrument station and a point on the ground. Apart from the subtend bar, in this method, no staff or target rod is needed. Further the theodolite needed is also of the ordinary transit type.

9. List the instrument errors in tacheometry survey. Explain any one with the necessary precautions. Errors caused in stadia tacheometry may be due to Instrumental errors Errors of observation Errors due to natural causes

Instrumental errors and precautions are given below.

(i) The permanent adjustments of the tacheometer may not be perfect. In order to avoid this, before starting the Survey all the adjustments needed for a tacheometer should be checked and rectified.

(ii) Graduation of the staff or stadia rod may not be uniform. In order to eliminate such errors, the staff and rod should be checked and corrected or should be replaced.

iii) Multiplying constant value may not be correct. In such situation, before starting of the work necessary field tests should be done to avoid this type of error.

UNIT-21. Distinguish between triangulation and trilateration. (A.U. Apr/May 2010)

Triangulation is a survey by which position of several stations are fixed very accurately on the surface of the earth at large intervals which serve as basis or reference points.

Trilateration is based on the principle that a triangle can be solved by knowing its three sides. Instruments like geodimeter. reflurometer. are employed. In geodetic survey this method is extensively used and the accuracy of the results is comparable o that of triangulation.

2. What are the different classifications of triangulation system? (A.U. Apr/May 2006)

Classification of a triangulation system is based on the accuracy with which the length and angle of a line of the r1angulati0n are determined. The following are the classification based on the order of grades:

First order or Primary Triangulation Second order or Secondary Triangulation Third order or Tertiary Triangulation

3. Give the specification of First order Triangulation. (A.U. May/June 2009)

Primary or First order triangulation is of the highest order. Following are the specifications:

Average triangle closure : Less than I second Maximum triangle closure Not more than 3 seconds Length of base line 5 to 15 km (iv) Length of the sides of triangles : 30 to 150

km Actual error of base I in 300000 Probable error of base 1 in 1000000 Discrepancy between two measures of a section 1 in 10 mm km Probable error of computed 1 in 60.000 to distance 1 in 250000 Probable error in astronomic azimuth: 0.5 seconds.

4. What is meant by Third order to Tertiary Triangulation (AU. Nov/Dec 2009)

Third order or Tertiary Triangulation Consists of a number of points fixed within the framework of secondary triangulation. These are the points which form the immediate control for engineering and other surveys.

5. Differentiate between Laplace stations from Satellite station. (A.U. Apr/May 2010)

At certain triangulation stations, astronomical observations for azimuth and longitude are also made which are called as Laplace stations.

Instruments cannot he set up over some stations like church spirals. towers of temple, etc. In such cases a subsidiary station called the satellite - station is selected as near as possible to the true station.

6. What is meant by phase of a signal?

When a cylindrical signal is partly illuminated and partly in shade, the observer sees only the illuminated portion and bisects it. The error of bisection thus introduced is called phase. It is the apparent displacement of the centre of the signal

7. What do you understand by eccentricity of signal?

Sometimes it is impossible to set up the instrument exactly over or under the signal which has been observed from the station points. Such a situation arises in traverse surveying and in triangulation surveying. In triangulation survey this happens when a leaning beacon or eccentric signal is observed.

In both the cases the instrument is set up near the signal at a “satellite station” or eccentric Station” or ‘lake station” and the angles are observed. The observed angles at each point are reduced to the centre.

8. What do you mean by figure adjustment in triangulation? (A.U. Nov/Dec 2006 and May/June 2007)

Figure adjustment is a system of triangles so arranged such that any figure has one side and only one common to each of the preceding and following.

9. What are the types of night signals to be used in triangulation survey? (A.U. Nov/Dec 2009)

Night signals are used for observing the angles of the triangulation system during night. Various forms of oil lamps and acetylene lamps are used.

10. Name two groups of people involved in the Measuring of the base line. A.U. Nov/Dec 2008)

The field work for the base-line measurement is carried out by two parties, viz, Setting out Party and Measuring Party.

Setting out Party consists of two surveyors and a no of porters. The duty of the porters is to place the measuring tripods, at correct intervals, in alignment in advance.

Measuring party consists of two observers, recorder leveller and staffman for actual measurement.

11. Name the different correction to be applied the length of a Base line.

Following are the corrections to be ai1ied the length of a Base line:

Correction for absolute length Correction for temperature Correction for pull or tension Correction for sag Correction for slope Correction for alignment Reduction to sea level

12. What is a base net Some site conditions may not be favourable to get the required length of a base line. In such a situation a short base line is selected and the same is then extended. Such group of triangles which are meant for extending the base is known as base net.

13. What are the types of trignometrical levelling?Trignometrical levelling are conducted considering the concepts of plane surveying or geodetic surveying. Accordingly they are grouped as

Observations to find small elevations and short distances. Observations to find higher elevations and large distances.

In the first case the principle of plane surveying is adopted. Here the effect of curvature and refraction are neglected and a proper correction is applied. In the second case, the effects of curvature and refraction are fully applied which are referred to as geodetic observations.

14. What are the refraction and curvature correction on linear measurements?

The line of sight is not perfectly straight as is imagined but it passes through layers of air having different densities. Due to refraction it bends towards the earth and thus the staff readings are affected. This is the error due to refraction.

Correction for refraction=0.07857

d2

¿0.0112d2

As the earth is not plain surface the staff readings are affected and this error due to the curvature of the earth is termed as error due to curvature.

Correction for cur vature=0.0785d2

where d is the distance between the instrument and staff station in km.

15. What are the curvature and refraction angular corrections?

The effect of curvature is to make the objects sighted to appear lower in position than they are in real position. On the other hand the effect of refraction is to make the object to appear higher than they really are. The combined effect of curvature and refraction is that the objects appear lower than they really are.

The angular correction for refraction

¿ mdRsin 1}} seconds ¿¿

The angular curvature correction

¿ d2Rsin1}} second ¿¿

The combined angular correction

¿ (1−2m )d2Rsin1}} second ¿¿

m = coefficient of refractiond = the horizontal distance between instrument and station.R = radius of the earth in m (381000 m).The combined correction is additive in the case of an angle of elevation and subtractive in the case of an angle of depression.

16. What is called axis signal correction?

At the stations, signals are erected at different heights. The signals may or may not be of the same height as that of the instrument. If the height of the signal is not the same as that of the height of the instrument axis above the station, a correction known as the axis signal correction or eye and object correction is to be applied.

17. What is the Single observation and name the corrections to be made?

In the Single observation method, the observations are made from only one station. The following corrections have to be applied for the observed angle.

curvature for correction refraction correction Axis signal correction. Further, the sign of these corrections depend on whether the angle is angle of

elevation or angle of depression.18. What is Reciprocal Observation?

In general reciprocal observations are made to eliminate effect of refraction. In this method simultaneous observations are made from both the stations so that refraction effect is same.

However, if it is not possible to take the observations on the same day on both the stations, it could be taken on the next day provided the refraction is almost same between 10 AM to 4 PM.

Reciprocal observation method is more accurate than the Single observation method, particularly when the exact value of coefficient of refraction is not known.

UNIT-31. What is meant by true value of the quantity? (A.U. Apr/May 2010)

Quantity is a measurement made in connection with a survey. The observed quantities may be classified as independent quantity, conditioned quantity and true quantity.

A quantity is said to be independent when its value is independent of the values of other quantities.

A quantity is said to be conditioned when its value is dependent upon the values of one or more quantities.

True value of a quantity is the value which is absolutely free from all the errors. The true value of a quantity is indeterminate since the true error is never known.

2. Explain the terms true error and most probable error. (A.U. Nov/Dec 2009)

A true error is the difference between the true value of a quantity and its observed value.

Most probable error is defined as that quantity which is added to. or subtracted from, the most probable value which fixes the limits. By these limits there s an even chance the true value of the measured quantity may lie.

3. Distinguish between true error and residual error. (A.U. May 2009; Nov 2006)

A true error is the difference between the true value of a quantity and its observed value.

A residual error is the difference between the most probable value of a quantity and its observed value.

4. What are the kinds of errors possible in survey work? (A.U. Nov/Dec 2006)

Error made on an observation may be due to some reason. Errors may be classified in a more general form as (i) mistakes, (ii) systematic error (iii) accidental error. Value of an error is also assigned as true, most probable and residual.

5. State the principle of method of least squares. (A.U. Apr/May 2008)

The fundamental principle of the method of least squares may be stated as:

“In observations of equal precision the most probable Values of the observed quantities are those that render the sum of the squares of the residual errors a minimum”.

6. What is the weight of an observation? (A.U. Nov/Dec 2006)

Weight of an observation is a measure of its relative worth which may be indicated by a number. Thus if a certain observation is said to have weightage 5, ( meant to say that it is five times as much as an observation of weight 1.

7. How are normal equations formed in theory of errors? (A.U. Nov/Dec 2009)

A normal equation is an equation of condition by means of which the most probable value of any unknown quantity may be determined corresponding to a set of values assigned to other unknown quantities. Therefore normal equations have to be formed for each of the unknowns, to determine their values.

8. Find the most probable value of the angle A from the following observation equations?

A=40°20' 12¿

2 A=80°40'20 ¿

6 A=40°20' 12¿

(A.U. Apr/May 2008)Solution

There is only one unknown and all the observations are of equal weight.

The coefficients in three equations are 1 2 and 6. Multiplying these equations by the respective coefficients

9. What is method of correlates?

Correlates are the unknown multiples or independent constants employed for finding the most probable values of unknowns.

Pin this method of correlates all the condition equations are collected. One more equation of condition, i.e., the sum of the squares of the residual errors should be minimum, is added.

10. What are the conditions to be satisfied when correcting the measured angles? (A.U. Nov/Dec 2008)

In field observation, the accuracy is checked at the end of the work by computing the closing error. In the case of angle measurement, the closing error is distributed to the observer angles. The distribution of error is followed by applying the following rules:

Correction to be applied to an observation is inversely proportional to the weight of the observation

Correction to be applied to an observation is directly proportional to the square of the probable error.

11. What do you mean by figure adjustment in triangulation?

Figure adjustment is the determination of the most probable values of the angles involved in any geometric figure as to fulfill the geometric requirement. It invariably

involves one or more conditional equations. Conditional equations may be framed by the method of normal equation or by the method of correlates.

12. What are the conditions to be satisfied when correcting the measured angles.

When several angles and their sum of equal weights are measured then the error is distributed equally among all the measured angles. When the angles measured are of different weights. The error is distributed among all the measured angles inversely as their respective weights.

13. What is single angle adjustment?

In general single angle is measured several times. Corrections to be applied are inversely proportional to the weight and directly proportional to the square of probable errors.

In case of equal weighted measurements the most probable value is equal to the arithmetic mean of the observations. In case of unequally weighted observation the most probable value of the angle is equal to the weighted arithmetic mean of the observed angles.

14. Why figure adjustment is made?

Figure adjustment is needed so as to fulfill the geometric conditions of any geometrical figure. The Figure adjustment therefore involves one or more condition equation

15. State Gauss’s Rule.

Gauss Rule is applied when the weights of the observations are not directly known. If the residual error of each observation is known the weights can be calculated by Gauss’s rule given by the following expression:

w=( n2

2 )∑ v2

where w is the weight to be assigned to a quantity.

n is the number of observations made for the quantity.

∑ v2 is the sum of squares of the residuals

16. What is called spherical excess?

In a spherical triangle the sum of the three angles of the triangles always exceeds 1800 by an amount known as spherical excess. Spherical excess depends on the area of a triangle. It may be taken approximately equivalent to 1” for every 196.75 sq.km.

17. What is method of equal shift?

Method of equal shift indicates that any shift which is necessary to satisfy the local equilibrium should be the same for each triangle of a polygon. Similarly any shift necessary to satisfy the side equation should be the same for each triangle.

18. Explain level net.

A level net is an interconnecting net work of level Circuits formed by level lines interconnecting three or more bench marks. In adjusting a level net, the method of least squares may be adopted.

UNIT-41. . What is a great circle? (A.U. Apr/May 2008)

If the earth is considered as a sphere any plane passing through its centre traces Out UOfl the surface a circle called the great circle. For example equator is a great circle.

2. Explain the term constellations of the zodiac. (A.U. Nov/Dec 2009)

For the purpose of classification the fixed stars have been arranged into groups known as constellations, the Stars in each group being either lettered or numbered.

The circle of twelve constellations through which the ecliptic passes constitutes the sign of the zodiac. The constellations taken in order are:

1. Aries (Ram) 7. Libra (The Balance)2. Taurus (Bull) 8. Scorpio (Scorpion)3. Gemini (Twins) 9. Stt (The Archer)4. Cancer (Crab) 10. Capricons (Goat)5. Leo (Lion) 11. Aquarius (Water-bearer)6. Virgo (Virgin) 12. Fisces (Fishes)

3. What is meant by celestial sphere? (A.U. Apr/May 2010)

For an observer upon the earth the fixed stars seem to be studded over the surface of a vast sphere, known as the celestial sphere at the centre of which the earth is approximately situated.

Because of the real rotation of the earth about its polar axis every twenty -four hours, the celestial sphere appears to rotate about the same axis during that time. The centre of the earth may be taken as the centre of the celestial sphere.

4. Name the properties of spherical triangle. (A.U.)

Following are the properties of a spherical triangle: Any angle is less than two right angles or π Sum of the three angles is less than six right angles or 3 π and greater than

two right angles or π. Sum of any two sides is greater than the third. If the sum of any two angles. is equal to two right angles or π the sum of the

angles opposite them is equal to two right angles The smaller angle is opposite the smaller side and vice-versa.

5. What are the corrections to be applied to the observed altitude of sun? (A.U. Nov/Dec 2008)

The observed altitude has to be corrected to obtain the true altitude. The corrections to be applied are

i. Instrumental corrections ii. Observational corrections.

Instrumental corrections are index Error and Bubble Error corrections.

Observational corrections are the following:

i. Correction for parallax. ii. Correction for refraction. iii. correction for dip of the horizon and iv. correction for semi-diameter

6. What is the correction for parallax when the altitude of celestial body is observed?

When the sun or star is viewed from different points change in the direction of the body is observed due to parallax. The parallax in altitude is called diurnal parallax. It provides data which are useful for surveyors and for practice of astronomical, navigation, etc.

Nautical almanac provides the following data:

Greenwich Hour angle of the sun. Equation of Time

Semi-diameter of the sun Sidereal Hour Angle Polar star tables

7. What is equation of time? Refer to Section 7.148. Distinguish between latitude and co-latitude. Refer to Sections 7.5.12 and 7.5.16

UNIT-51. What is photogrammetry? (A.U. Nov-Dec 2006)Photographic surveying or Photogrammetry is the art of producing plans or maps from photographs. Here the photographs are taken from a suitable camera position.Photographic surveying, in principle, is very similar to that of Plane Table surveying, with the difference that most of the work, which the tatter instrument is executed in the field, is here done in the office.2. 2. What are the branches of photogrammetry?There are two broad branches of photogrammetry. Photographs taken from a fixed position on or near the ground and the branch deals on such aspects is called Terrestrial photogrammetry. Aerial photogrammetry is the other branch wherein the photograph are taken by cameras mounted on an aircraft flying over the area.3. 3. List the uses of photogrammetry. Following are the uses of photogrammetry.

(i) Construction of planimetric and topographic maps.(ii) Satisfactory survey of mountainous and hilly areas with less number of

trees.(iii) Aerial survey is most suitable for reconnaissance. (iv) Suitable for inaccessible regions forbidden properties, unhealthy regions

like malarial affected areas.(v) Acquisition of military intelligence.(vi) Interpretation of geology and soil details.(vii) Has been largely used for the surveys of buildings.

4. Explain the need for overlap in aerial photography.(A.U. Nov 2006) Overlap of photographs in the direction of flight line is called longitudinal or forward overlap. The overlap between adjacent flight lines is called the lateral overlap.General reason for providing an overlap is to make sure that no part of the ground is unrecorded.

5. What is meant by scale of photograph? Scale of a photograph is obtained from the ratio of the distance of any two points on the photograph and the distance between the corresponding points on

the ground. The two points chosen for scaling should lie nearly equidistant on either side of the principal point

6. What are crab and drift? (A.U. May/June 2010)The angle formed between the flight line and the edges of the photograph in the direction of flight is designated by a term called ‘crab’. The crab is caused in the photograph when the focal plane of the camera is not with the direction of flight. SueyingnDrift is caused by the failure of the photograph to stay on the predetermined tlight line. If an aircraft is allowed to go on its course without allowance for wind velocity, it will drift.

7. Define angle of parallax.As an object is simultaneously viewed by two eyes, the two rays of vision converge at an angle upon the viewed object. The angle of convergence of these two rays of vision is called the angle of parallax or the parallatic angle.

8. Explain stereoscopic fusion.Consider a pair of photographs taken of an object from two slightly different positions by a camera. The view of the camera ensures that the left-eye sees only the left hand picture and the right-eye the right hand picture.These two separate images of the object will fuse together in the brain to provide the observer with a spatial impression. This is known as stereoscopic fusion. The pair of such photographs is called as stereo pair.

9. How the V scale in a Beaman Stadia Arc is designed. V-scale is designed such that sin 2θ for each graduation is a magnitude of 0.01. For example when the index reads 51 (or 49), the line of sight is inclined by an angle corresponding to the first division on the arc ½ sin 2θ. For this the θ value is 34’23”.

10. List the functions of an EDM. The functions of EDM are:(i) Generation of carrier wave and measuring wave frequencies.(ii) Modulation and demodulation of the carrier wave.(iii) Measurement of the phase difference between the transmitted and received measuring waves.(iv) Display in some form, the result of this measurement.

11. What is a photo-theodolite? (A.U. Apr/May 2008)Photo-theodolite is a combination of a camera and a theodolite. It consists of (i) a fixed focus type camera, (ii) a circular magnetic compass, (iii) a telescope mounted on the top of the camera. (iv) a horizontal circle is graduated and provided with a vernier, and (v) a levelling head.

12. What is a box-sextant? What are its uses? (A.U. Apr/May 2008)A box - sextant is a reflecting type of instrument used for measuring horizontal and vertical angles. The optical principle on which the box-sextant is constructed is that the angle between the two objects is twice the angle between the mirrors.

13. List the main parts of an aerial camera. The main parts of an aerial camera are:

(i) Magazine

(ii) Focal plane(iii) Body of the camera(iv) Trunion(v) Camera cone(vi) Lens(vii) Shutter(viii) Diaphragm(ix) Filter(x) Drive mechanism

14. Distinguish between mirror and lens stereoscopes. Mirror stereoscope consists of four mirrors, two of which are small eye - piece mirrors. Other two mirrors are large mirrors which are oriented with the plane of the photographs at 45o. The four mirrors transfer the light to the eyes exactly as if it had come from the object.In lens stereoscopes no mirrors are provided but magnifying lenses are used. These are mounted with a separation equal to the average inter pupillary distances of the human eyes.

15. What are lunar and solar tides? (A.U. Nov/Dec 2008)

The periodical variations in natural water level are called as tides. The resultant force between the earth and moon causes lunar tides. Lunar tides may be super lunar tide or inferior lunar tides depending on the moon’s transit.

The phenomenon of production of solar tides is due to force of attraction between earth and sun which is similar o the lunar tides. Thus there will be superior solar tide or inferior solar tide.

16. What is meant by sounding? (A.U, Apr/May 2010)

The measurements of depths below the water surface are called soundings. This is synonymous to the depth measurement in land with reference to a datum. The aim in making soundings is to determine the configuration of the subaqueous source.

17. Name the different equipment needed for soundings. (AU. )

A boat along with the following equipment is needed for sounding:

Sounding rods or poles Lead lines or sounding cables Fathometer

Sounding rod or pole is a wooden or a bamboo pole of 5 cm diameter and of 2.5 m length. A disc of 15 cm diameter is fixed at the bottom of the pole and the pole is graduated in metres and 1/10th of a metre.

Sounding cable is used in cases where the depth is more than 2m and with high water current. A weight of 5 kg is attached to the cable.

Fathometer is also called as eco-sounder which is used tor measuring depth of large rivers and of seas with depth of more than 10 m.

18. List the different methods of locating soundings. Explain any two methods. (A.U. May/June 2009)

Methods locating of soundings are:

By cross rope. (ii) By range and time intervals. (iii) By range and one angle from the shore. (iv) By range and one angle from the boat. (v) By two angles from the shore. (vi) By two angles from the boat. (vii) By one angle from shore and one angle from the boat. (viii) By intersecting ranges. (ix) By tacheometry.

Refer o Section 6.4.4 for explanation of any two methods.

19. What is three point problem in hydrographic surveying? What are the various solutions for the problem? Explain any one method. (A.U. May/June 2009; Nov/Dec 2009)

If a sounding is located by two angles from the boat by observations to three known points on the shore, the plotting can be done adopting three-point problem. The three point problem may be solved by mechanical, graphical or analytical methods.

Refer of Section 6.7.1 for any one method.

20. Name the different methods of finding discharge.

In order to determine the discharge of a river, the current Velocity of flow and cross-section of the river should be known. The methods to measure velocity are

current meter method pitot tube method surface float method subsurface float velocity rod method

21. Why a river gauging is done?

River gauging is carried out so as to assess the following:

In order to fix the number of spans of a road or railway bridge so as 10 avoid any damage to the structure due to high floods.

In order to fix the height of the guide hank. In order to decide the spillway level and the height of the barrage or darn.

In order to design cross-drainage works when a canal crosses a river.22. Name the factors to be considered in the selection of a discharge

site.

The following are the factors:

The river should he straight for four times its width or atleast for a minimum length of about 500 m.

The cross-section of the discharge should he well-defined The flow of the river should confine to one channel. The centre line of the river can he identified with reference to the targets

installed on the bank of the river.