Showing posts from January, 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 another 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  Leveling headlower circular plateUpper plateTelescopeVertical circle There are some fundamental lines of Transit Theodolite: Vertical axisHorizontal axis or Trunion axisAxis of the altitude bubble or Azimuthal axisLine of collimationA…

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 mWhen 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 …

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 po…

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.Tell…

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 …

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 accu…

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 …