survey Flashcards
chain types and lenghts
20m/30m Metric chain
66 feet (100 link) Gunters chain
100 feet Engineers chain
33 feet (16 link) Revenue chain
sag correction in chain survey
W^2 L /(24P^2)
limitng length of offset error allowed on paper
- 025 cm
difference between bowdich method and transit method of closing error correction
Bowditch method - angles and lengths are of equal precision
Transit method - Angular measurement more precise
probable errors of given weights and deviations
for single measurement of unit weight e = 0.6745 *σn-1 for error in most probable value ep = e / sqrt(ΣW) for error in single value of weight W ew = e / sqrt(W)
Plum point
Perspective point
principal point
in areal photograply
Plum point: A point where the vertical through the optical centre meets the photograph.
Perspective point: A point where the rays from the objects converge.
principal point: A point where the perpendicular from the optical centre of the lens meets the photograph
Horizontal stave / subtense bar in techometric survey
Horizontal stave, also known as subtense bar, used for measuring both the horizontal as well as vertical distance in place where chaining is impossible
Spire test in used for adjustment of ?
Spire test in used for adjustment of horizontal axis.
Classification based on the nature of field survey
- Land survey
- Marine or hydrographic survey
- Astronomical survey
Classification based on object of survey
- Engineering survey
- Military survey
- Mine survey
- Geological survey
- Archeological survey
Classification on instrument used
- Chain survey
- Theodolite survey
- Traverse survey
- Triangulation
- Tacheometric survey
- Plane table
Vernal equinox?
Vernal equinox, two moments in the year when the Sun is exactly above the Equator and day and night are of equal length; also, either of the two points in the sky where the ecliptic (the Sun’s annual pathway) and the celestial equator intersect.
Sensible horizon?
Sensible horizon at a point on earth surface is a circle in which a plane passing through a point of observation and tangential to the earth’s surface intersects the celestial horizon.
prismatic compass and surveyor compass
prismatic small size readings in W.C.B simultaneous reading and sighting tripod not essential graduation inverted graduations on needle body
surveyor compass bigger circular box 150 mm dia quadrantal bearing first sighted then reading tripod is essential graduations are erect and separate from needle
telescope normal and telescope inverted
normal = when vertical side is on left
and vice versa
swinging of telescope
transiting of telescope
revolving in horizontal plane
revolving in vertical plane 180 degree
temporary adjustments of theodolite
setting centering leveling focusing of eye piece focusing the objective
radiation method
it is suitable when area to the surveyed is small and all the required station are clearly visible and accessible from instrument station
resection method
it is employed when plane table occupies a position not yet plotted on the drawing sheet. it is commonly used for establishing instrument station
two point and three point problem
intersection method
it is used when the base station are visible and accessible but the other stations are only visible not accessible. it is most suitable for hilly area and also known as graphical triangulation
traversing method
generally used when a narrow strip of terrain is to be surveyed. ex-survey of road, railway etc. used for both open and close traverse
plane table surveying types
https://theconstructor.org/surveying/plane-table-surveying-methods-examples/12877/
clinometer
pantagraph
tellurometer
ghat tracer
clinometer =angle measuring instrument
pantagraph = plan enlarging instrument
tellurometer = microwave measurement, EDM
ghat tracer = gradient finding instrument
farthometer
instrument used for measuring depth in ocean
geodimeter
geodimeter is a medium range < 25km, electronic distance measuring equipment. it has a range of 5km in day, 25km in night using mercury lamp
five types of vernier direct vernier- retrograde vernier- double vernier- double folded vernier extended vernier
direct vernier-
divisions slightly shorter then main
retrograde vernier-
divisions slightly longer then main
double vernier-
it is used when graduations on the main scale are numbered in both directions. the double vernier extends in both directions with index mark in the center, it is combination of two direct verniers
double folded vernier-
it is a special type of double vernier whose total length is 1/2 of combined length of corresponding double vernier. it is used when required to keep the length of vernier short
extended vernier-
divisions of the vernier scale are equal in length (2n-1) divisions of main scale. An abney level has an extended type of vernier with a least count of 5’ or 10’
error types introduced in Theodolite survey
INSTRUMENTAL errors
- imperfect adjustment of plate levels
- line of collimation not being perpendicular to horizontal axis
- horizontal axis not being perpendicular to vertical axis
- eccentricity of inner and outer
- eccentricity of verniers
- imperfect graduations on horizontal scale
- vertical index error
- vertical cross hair not perpendicular to horizontal
- defective tripod
PERSONAL ERRORS
- errors in manipulation = inaccurate centering, inaccurate leveling, slip in screws and improper use of tangent screws
- errors in sighting and reading
ERRORS DUE TO NATURAL CAUSES
temprature, wind , refraction effect, settlement of tripod
Transit Theodolite:
Transit Theodolite:
A theodolite is said to be a transit one when its telescope can be revolved through 180° in a vertical plane about its horizontal axis, thus directing the telescope in exactly opposite direction.
The vertical circle is rigidly fixed to the telescope and rotates with the telescope.
find internal angles and foreberings again from internal angles
if: we are going clockwise sequence
< B = < BA - < BC (BB-FB)
else if : anti-clockwise
< B = < BC - < BA (FB-BB)
converting back from internal angles if: we are going clockwise sequence < BC = < AB+ (180 - < B) else if : anti-clockwise < BC = < AB - (180 - < B)
