Monday, January 20, 2014

Classifications of Theodolites

Hello there,

Theodolite is one of the basic instrument which has many uses including traversing. Theodolite is broadly classified into two categories:

  • Transit Theodolite In this type of Theodolite, line of sight can be reversed by revolving the telescope 180 degrees along the vertical plane.

  • Non-Transit Theodolite In this type of Theodolite, the line of sight can not be revolved in the vertical plane.
There are other classifications of the Theodolite:
  • Vernier Theodolites.
  • Micro-meter Theodolites.
Size of Theodolite: This is defined by the diameter of the graduated circle of the lower plate. Common sizes are 8 cm to 12 cm while 14 cm to 25 cm are used for triangulation work or you can say for more precise works.


Main parts of a transit vernier Theodolite are 
  1. Leveling head
  2. lower circular plate
  3. Upper plate
  4. Telescope
  5. Vertical circle

There are some fundamental lines of Transit Theodolite:
  1. Vertical axis
  2. Horizontal axis or Trunion axis
  3. Axis of the altitude bubble or Azimuthal axis
  4. Line of collimation
  5. Axis of the plate bubble
  6. Axis of striding level if present.
Thanks for kind visit!

Tuesday, January 7, 2014

Surveying notes for GATE and PSUs exams. - Part 11

Hello there, 
The following facts are taken from many references, mainly from the book titled "Civil Engineering objectives" by S P Gupta and S P Gupta.
  • Bowditch method has used the assumptions:  Errors in linear measurements are proportional to under root of L.; Correction to latitude or departure of any side = Total error in L(or D) * (Length of that side/ Perimeter of traverse).
  • To determine the length of a bridge proposed to be built across a wide river, the triangulation method of surveying will be preferred over tacheometry, chain surveying.
  • Heliograph is a type of sun signal used in triangulation work.
  • A 100 m tape is held 1 m out of line. The true length will be 99.995 m
  • When the line of collimation is not perpendicular to the horizontal axis taking face-left and face-right observations reduces the error.
  • It is not necessary to do the exact centering of plane table to do the small scale surveys.
  • Saddle line is also known as ridge line or valley line.
  • Line of drainage basin is the line which passes through ridges and saddles setting up a domain.
  • Longitude of a place is measured by wireless time signal and transportation of chronometers.
  • In tilting level the vertical axis is not perpendicular to the line of collimation.
  • Inverted staff readings are taken for the points above the line of collimation.
  • Reciprocal levelling eliminates the error due to inclined line of collimation also.
Thanks for visit!

Monday, January 6, 2014

Surveying notes for GATE, PSUs - Part 10

Hello there,
How have you been? Here is 10th part of one liners for the preparation of the GATE and PSUs.
All information is learned through books and practical exercises.
  • To find the R.L. of a roof slab of a building, staff readings were taken from a particular set-up of the levelling instrument. The readings were 1.050 m with staff on the benchmark and 2.300 m with staff below the roof slab and held inverted. Taking the R.L. of the B.M. as 135.150 m, the R.L. of the roof slab will be 138.500 m.
  • Operations involved in a spire test are : 1) Sight a well-defined high point on a high building 2) Clamp horizontal plates  3) Depress the telescope and sight a point on the ground nearer to the instrument 4) Change face and repeat the procedure.
  • Accurate centering in plane table surveying is necessary for large scale maps.
  • Exact orientation is more important than accurate centering for small scale maps.
  • The intersection method of plane table surveying is particularly employed for inaccessible points.
  • Plane table survey is useful for open country with good inter-visibility.
  • Simpson's method estimates best the area of an irregular and curved boundary.
  • In a closed traverse, the sum of south latitudes exceeds the sum of north latitudes and the sum of east departures exceeds the sum of west departures. The closing line will lie in N-W quadrant.
  • In reciprocal levelling, the difference in elevation of two points is calculated by taking the average of the differences obtained by taking measurements from two different instrument settings, one at near to first station and second at near to second station.
  • A lemniscate curve between the tangents is transitional throughout,the polar deflection angle of its apex is equal to A/6.
Other parts :

Saturday, January 4, 2014

Surveying notes for GATE, PSUs - Part 9

Hello there,
How have you been? Here is 9th part of one liners for the preparation of the GATE and PSUs.
All information is learned through books and practical exercises.

  • If quantity A has a weight of 3, then the weight of A/3 will be 27.
  • In a parabolic vertical curve, the rising grade g1= +0.80% and the falling grade g2= -0.70%. The rate of change of grade is 0.05 per chain, then the length of the vertical curve is 30 chains.
  • While measuring horizontal angles by the method of repetition with a theodolite, readings are taken on both the vernier. Error due to imperfect graduations will be eliminated.
  • An angle-measuring instrument reading up to one-sixth of a degree on the main scale is equipped with a vernier having 19 main scale divisions divided into 20 parts. The correct least count for the instrument is 30 seconds.
  • If it is required to produce the plan of a small area under the magnetic influence, plane table survey will be the best choice.
  • Clinometer- An angle measuring instrument.
  • Tellurometer - microwave instrument
  • Pantograph- Plan enlarging instrument
  • Ghat tracer - Grading finding instrument.
  • Offsets are lateral measurements made with respect to main survey line.
Other parts :

Friday, January 3, 2014

Surveying notes for GATE, PSUs - Part 8

Hello there,
How have you been? Here is 8th part of one liners for the preparation of the GATE and PSUs.

  • A curve tangential to four straight lines and consisting of arcs of different radii is known as three centred compound curve.
  • The length of the tangent of a curve of radius R and angle of deflection D is given by R.tan(D/2).
  • The length of the long chord of a simple circular curve of radius R and angle of deflection D is 2R.sin(D/2).
  • Setting out a curve by two Theodolite method does not require linear measurements.
  • If r is the radius of curvature at any point of a transition curve and l is the distance from the beginning of the transition curve to that point, then for ideal transition l is inversely proportional to r.
  • In a reverse curve, the super-elevation provided at the point of reverse curvature is zero.
  • Total angle of deflection of a spiral curve is (spiral angle/4).
  • The shape of vertical curve generally provided is parabolic.
  • Perpendicular offset from the junction of transition curve and circular curve to the tangent is equal to four times the shift.
  • If  L is the length of transition curve and R is the radius of circular curve, then the shift of the curve is directly proportional to L^2 and inversely proportional to R.
  • The difference in elevation of points between a vertical and a tangent is directly proportional to the square of its horizontal distance from the point of tangency.
  • Shift bisects the transition curve and transition curve bisects the shift.
  • The maximum value of centrifugal ratio on roads and railways respectively are 1/4 and 1/8.
  • Agonic line is the line joining points having zero declination.
  • For a circumpolar star, declination must be more than co-latitude.
  • For a star at its upper transit, the local sidereal time is equal to R.A. of the star.
  • Sidereal year(SY) is greater than Tropical year(TY).
  • The limiting minimum value of declination of a circumpolar star having latitude 40 degrees North is (90-40) = 50 degrees.

All information is learned through books and practical exercises.

Thanks for visit!

Thursday, January 2, 2014

Surveying notes for GATE, PSUs - Part 7

Hello there,
How have you been? Here is 7th part of one liners for the preparation of the GATE and PSUs.
  • Two point problem and three problems are methods of orientation and resection.
  • Resection by two point problem requires more labor than by three point problem.
  • Methods used to locate the plane table station are resection and traversing.
  • After fixing the plane table to the tripod, the main operations which are needed at each plane table station are levelling, centering and orientation respectively.
  • Bowditch rule is applied to a closed traverse for adjustment of closing error.
  • If in a closed traverse, sum of south latitudes is more than sum of north latitudes and also sum of east departures is more than west departures, the bearing of closing line is in NW quadrant.
  • The angle between prolongation of preceding line and the forward line of a traverse is called deflection angle.
  • Transit rule of adjusting the consecutive co-ordinates of a traverse is used where angular measurements are more accurate than linear measurements.
  • While theodolite traversing, angles are measured from at least two stations to locate a  point which is at a far distance.
  • Subtense bar is an instrument used fr measurement of horizontal distances in undulated areas.
  • Horizontal distances obtained by tacheometric observations do not require slope and tension corrections.
  • There are three horizontal corss hairs- in a stadia diaphragms.
  • In movable hair method, the intercept on leveling staff is kept constant and stadia hair interval is variable.
  • In fixed hair method the intercept on leveling staff is variable and stadia hair interval is fixed.
  • In tangential hair method the stadia hairs are not used.
  • The angle subtended by the long chord of a simple circular curve at its centre is equal to angle of deflection.
All information is learned through books and practical exercises.

Thanks for visit!

Wednesday, January 1, 2014

Surveying notes for GATE, PSUs - Part 6

Hello there,
How have you been? Here is 6th part of one liners for the preparation of the GATE and PSUs.

  • In Levelling, a station is the point where the levelling staff is held and not where level is set up.
  • The inner surface of a bubble tube is an arc of a circle.
  • Sensitivity of a level tube can be increased by the increase in length of bubble.
  • Dumply level is most suitable when a numbers of readings are to be taken from single setting of the instrument.
  • The difference of levels between two stations A and B is to be determined. For best results, the instrument station should be equidistant from A and B.
  • contour interval is inversely proportional to the scale of the map.
  • An imaginary line lying throughout the surface of ground and preserving a constant inclination to the horizontal is known as contour gradient.
  • Two contours of different elevations do not cross each other except in case of an overhanging cliff.
  • A series of closely spaced contour lines represents a steep slope.
  • Direct method of contouring is most accurate method.
  • In direct method of contouring, the process of locating or identifying points lying on a contour is called vertical control.
  • In the cross section method of indirect contouring, the spacing of cross-sections depends upon contour interval, scale of plan and characteristics of ground.
  • For hilly terrains Tacheometric method of contouring is most suitable.
  • contour interval for any map is kept constant.
  • Closed contours, with higher values inside represents a hillock.
  • Benchmark is established by spirit leveling.
  • Plane table is the type of survey which requires least office work.
  • Intersection method of detailed plotting is most suitable for hilly areas where the points are not accessible.
  • Detailed plotting is generally done by radiation method.
  • Three point problem can be solved by Tracing paper method, Bessels method and Lehman's method.
  • The size of a plane table is 600 mm * 750 mm.
  • The process of determining the locations of the instrument station by drawing resectors from the  locations of the known stations is called resection
  • Plumbing fork is used for accurate centering of plane table.
Thanks for visit!

Solved Example-Distance of a Point from a Line, whose end Co-ordinates are given.

Hi, Problem: The X and Y co-ordinates(in meters) of station Shore are 246.87 and 659.46 respectively, and those for station Rock are 437...

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