BTEB Amin Survey Exam flashcards

34 cards. Read the term and the definition here. The deck at the top of this page is optional.

Plane surveying limit

Plane surveying treats the earth's surface as flat and is acceptable for areas up to about 250 square kilometres; beyond that, curvature must be considered and geodetic surveying is used.

Gunter's chain length

A Gunter's chain is 66 feet long and divided into 100 links, so each link is 0.66 feet or about 0.2012 metres; 1 metre equals about 1.515 links.

Positive cumulative error

A positive cumulative error makes measured lengths too great; it arises when the chain is too long, the pull exceeds standard, or the slope correction is omitted.

Optical square function

An optical square uses two mirrors set at 45 degrees to each other to establish a line at exactly 90 degrees to the chain line when setting offsets.

Ranging definition

Ranging is fixing intermediate points on a straight survey line; direct ranging is used when the ends are intervisible, indirect ranging when they are not.

Magnetic declination

Magnetic declination is the angle between true north and magnetic north; true bearing equals magnetic bearing plus east declination or minus west declination.

Local attraction test

Local attraction is detected when the difference between fore bearing and back bearing of a line is not 0 or 180 degrees; the affected bearings are corrected from an unaffected line.

Interior angle formula

For a closed traverse with n sides, the sum of interior angles equals (2n minus 4) multiplied by 90 degrees; the angular error is the measured sum minus this value.

Bowditch rule

The Bowditch or compass rule distributes traverse closing error in proportion to leg length; the correction to each latitude or departure is the total error times that leg over the perimeter.

Latitude and departure

Latitude is the north-south component of a traverse leg, equal to length times cosine of bearing; departure is the east-west component, equal to length times sine of bearing.

Height of collimation

Height of collimation is the reduced level of the instrument line of sight, found by adding the backsight reading to the benchmark reduced level; intermediate sights are subtracted from it.

Rise and fall check

In the rise and fall method, the sum of backsights minus the sum of foresights equals the sum of rises minus the sum of falls, which equals the last reduced level minus the first.

Combined curvature correction

The combined correction for curvature and refraction is minus 0.0673 times distance squared in kilometres; it is always subtractive from the staff reading.

Reciprocal levelling

Reciprocal levelling takes sights from both banks of a wide river; averaging the two results eliminates curvature, refraction, and collimation errors.

Contour interval

Contour interval is the constant vertical distance between adjacent contours on a map; horizontal spacing varies with slope and is smallest where the ground is steepest.

Orientation by backsight

Orientation by backsight sets the plane table so a plotted line points at its ground station; the alidade is sighted on a known point and the table rotated until the line coincides.

Radiation method

In the radiation method, the plane table occupies one station and rays are drawn to all detail points, with distances scaled along each ray from the station.

Intersection method

In the intersection method, the table occupies two known stations and rays are drawn from each; the intersection of corresponding rays fixes each detail point without linear measurement.

Three-point problem

The three-point problem locates the plane table station from three known plotted points; the Lehmann method uses the triangle of error to find the correct position.

Planimeter area formula

A planimeter gives area as the multiplier constant times the difference between final and initial dial readings; the zero circle is traced when the roller passes over the pole.

Simpson's rule

Simpson's rule computes area as one third of the interval times the sum of first and last ordinates plus four times even ordinates plus two times odd ordinates.

Trapezoidal rule

The trapezoidal rule sums half the first and last ordinates plus all intermediate ordinates, then multiplies by the constant interval between ordinates.

Prismoidal formula

The prismoidal formula gives volume as one third of the interval times first plus last areas plus four times even areas plus two times odd areas; it is more accurate than end-area.

Coordinate area formula

The shoelace formula gives twice the area as the cyclic sum of x times next y minus next x times y; the magnitude is the area and the sign shows orientation.

Tangent length of curve

For a simple circular curve, tangent length equals radius times tangent of half the deflection angle; curve length equals radius times the deflection angle in radians.

Deflection angle per chord

The deflection angle for a chord of length c on a curve of radius R is c divided by twice R, expressed in radians and converted to seconds by multiplying 206265.

3-4-5 right angle

A triangle with sides in the ratio 3:4:5 has a right angle between the two shorter sides; it is used to set out perpendiculars on site without a theodolite.

Transition curve length

Transition curve length is often taken as velocity cubed divided by constant C times radius; it limits the rate of change of centrifugal acceleration.

Field book rule

Field book entries are made in hard pencil, never erased; a wrong value is struck through with one line and the correct value written beside it.

Levelling book columns

A levelling field book records station, backsight, intermediate sight, foresight, rise, fall, height of collimation, and reduced level, with arithmetic checks at the page bottom.

Face left and right

Face left and face right theodolite readings are averaged to eliminate collimation error and errors of horizontal axis adjustment; the difference should be 180 degrees.

Representative fraction

Representative fraction is the ratio of map distance to ground distance in the same units; 1:1000 means one millimetre on the map equals one metre on the ground.

Plan versus map

A plan is a large-scale drawing of a small area, generally at 1:1000 or larger; a map is a small-scale drawing of a large area.

Professional negligence

A surveyor is liable for negligent misstatement when a client relies on an inaccurate survey report; professional indemnity insurance covers such errors and omissions.