Surveying

Surveying 

The science of determining the position

• Surveying defined as taking measurement of the relative positions of natural and manmade features on the earth’s surface and presentation of this information either graphically or numerically.
• The common method of presentation is by way of a plan or a map true-to-scale representation of an area in the two dimensions, which form the horizontal plane.

Surveying

• Art of measuring distances, angles, and positions above, on or below the earth’s surface.
• The relative positions of points are located by means of measuring distances, directions and angles accurately with the help of various surveying instruments.
• Surveying also includes the art of locating or setting out points on the ground from a plan or a map.

Purpose

• To determine the relative positions of points on the earth’s surface to locate arbitrary points, configuration of the ground, direction and length of lines, boundary lines, etc.,
• To set out the lines and steps needed for the construction of buildings, roads, dams, and other structures,
• To calculate areas, volumes and other related quantities,  
• To prepare necessary maps and diagrams of an area.

Purpose of surveying:

1. Land Surveying:

The measurement of existing land, buildings and other man made features

2. Setting –out:

The operation necessary for the correct positioning of proposed works on the ground and their dimensional control during the construction process

Two kinds of surveys

1. Plane surveying
2. Geodetic surveys

Plane survey

• Because of the limited extent of the survey, The curvature of the earth can be ignored
• Can be considered as flat planes  (up to 250-300 km2)
• For most engineering projects such as canal, railway, highway, building, pipeline, etc. constructions, this type of surveying is used.
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Geodetic surveys

• Measured a large part of the surface of the earth that the curvature of the earth cannot be ignored.
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Classification of Surveys

Traverse

This land survey Technique is commonly used for creating Preliminary Surveys of the Building, new Roads, etc.

Advantages

• Less exploration and organization needed
• While in other systems, require the survey to be performed along a rigid polygon shape, the traverse can change to any shape and accommodate a great deal of different terrains
• Only a few observations need to be taken at each station, whereas in other survey handle a great deal of angular and linear observations

Surveying by offsets (polyline or polygon)

Triangulation

• Use series of connected triangles that join and overlap each other, and from there angles can be measured from determined stations.
• Most commonly used land survey technique
• Very efficient as it minimizes the number of measurements that need to be made.
• Location by three measured sides.

Trigonometric

The total station calculates change in height using trigonometry:

Basic Measurements and Instruments

• Surveying consists of four basic measurements:

Horizontal distance – measured by tapes, chains, tacheometers, EDM, pacing, odometer, etc.

Vertical distance – measured by levels, tacheometers.

Horizontal angles – measured by theodolites, compasses.

Vertical angles – measured by theodolites, clinometers.

• Distance Measuring Methods--GPS
  
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  GPS (global Positioning System) is a system of 21-24 satellites in orbit around the earth.
• Each satellite knows its position and uses a unique signal to continuously broadcast this information.
• Along with the position information is a time signal.

• When a GPS receiver receives a signal from at least four (4) satellites it can compute its position by trilateration.

Universal Transverse Mercator (UTM)

• The receiver position can be expressed in degrees of latitude and longitude, or distance (meters) using Universal Transverse Mercator ( UTM) coordinates.
• The Universal Transverse Mercator (UTM) conformal projection uses a 2-dimensional Cartesian coordinate system to give locations on the surface of the Earth.

Distance Measuring Methods—GPS

• Because UTM distances are based on a x-y coordinate system distances between points can be determined by simple math.
• Example:  Determine the distance between Stillwater and Oklahoma City when the UTM coordinates for Stillwater are 675087E & 3998345N  and the UTM coordinates for  Oklahoma City are 639982E & 3925518N

  

Note: this is the plane distance between these points not the surface distance.

Scale

A scale represented as;

1. Engineer’s scale

1 cm = 10 meters

2. Representative Fraction (R.F.)

1 /500, 1/1000 or 1:500, 1:1000

1 cm = 50 m as R.F.

1 cm / 50 x 100 cm = 1/5000

Actual length of 50 m represented by 100 mm what is the RF?

For maps

1. Large scales < 1:200
2. Intermediate scales 1:2000 to 1:10,000
3. Small scales 1:10,000 to 1:100,000,000

For plans

1. Site plans 1:50 to 1:500
2. Detail plans 1:1 to 1:20

Type of survey	Engineers Scale	R.F.
Building sites	1 cm = 10 m or less	1 / 1000
Town plans	1 cm = 50 - 100 m	1/5000 - 1/10000
Location surveys	1 cm = 50 - 200 m	1/5000 - 1/20000
Small  scale  topographic  maps	1 cm = 0.25 - 2.5 km	1/25000 - 1/250000
Cadastral map	1 cm = 5 m - 0.5 km	1/500 - 1/5000
Geographical map	1 cm = 5 km - 160 km	1/500000 - 1/16000000

Plane Surveying

1. Chain Surveying
2. Plane table surveying

Survey - Drawing

• Field Notes
• Final Office Plotting Information:
• Scale & units  A north point
• Map references
• The date  The surveyor’s name
• The draughtsman's name
• The drawing number

Chain Surveying- Equipment’s

• The chain

• Gunter’s Chain- 66  ft. long
• Metric chain- 20-50 m long chains
• Engineer’s chain- 100  ft. chain

• Compass
• The steel band & tape
• Arrows
• Ranging poles
• Plumb-bob
• Offset measuring equipment’s
• Clinometers & Abney level

Early Surveyors’ equipment’s

Plumbob

It is used while chaining along sloping ground, to transfer the points to ground surface. It serves the purpose of making ranging poles vertical and to transfer  points from a line ranger to the ground.  It can also be used as centering aid in theodolites, compass, plan table and a variety of other surveying instruments. 

Measuring Distance

The historical method for measuring distance is the surveying chain.

• One of the first chains used in the U.S. was the Gunter‟s chain.
• The Gunter‟s chain was a series of  links attached to a handle which included an adjustment for wear.
• The chain was 22 yards (66 ft) long.
• These chains were replaced by 100 foot steel chains.
• In recent years surveyors have switched to plastic coated steal chains.

Chain Surveying - Steps

1. Preliminary inspection: A rough sketch of the area is made in the field book
2. The base line: Normally the longest of the chain line forming the pattern of triangles. It should be laid off on level ground      through the center of the site
3. Divide the area into as big triangles as possible and then sub divide them in to smaller triangles. None of the angles of a triangle should be less than 300 no more than 1200.

Survey line

Base Lines:

• It is main and longest line, which passes approximately through the centre of the field. All the other measurements to show the details of the work are taken with respect of this line.
• Tie or subsidiary lines:
• A tie line joints two fixed points on the main survey lines. It helps to checking the accuracy of surveying and to locate the interior details. The position of each tie line should be close to some features, such as paths, building etc.
• Inset or offset at an angle other than a right angle to a main chain line or other line

Survey lines- Check line

• A check line also termed as a proof line is a line joining the apex of a triangle to some fixed points on any two sides of a triangle. A check line is measured to check the accuracy of the frame work. The length of a check line, as measured on the ground should agree with its length on the plan.
• The length of the check line on the field should be the same as when plotted on paper

Offsets

• These are the lateral measurements from the base line to fix the positions of the different objects of the work with respect to base line.

These are generally set at right angle offsets.

It can also be drawn with the help of a tape. There are two kinds of offsets:

• 1) Perpendicular / right angle offsets, and 2) Oblique/tie line offsets -not made at right angles

Offsets

Location of an object by offsets

• Rectangle/right angle offsets
• Oblique offsets
• Measuring direction and distance
• By two angles from the ends of measured line

Offsets-distance measured from the chain line to the objects

Offsets- Rectangle/right angle

• Rectangular offsets

Setting out right angles (Offsets)

• 1 . By swing offset method
• 2 . Right angle triangle method  (3,4,5 Method )
• 3 . By cross staff
• 4 . By optical square / Prism square

• Oblique offsets

Measuring direction and distance

By two angles measured from ends of a measured base line

Bearing

• Whole circle Bearing
• Quadrantal (Reduced) Bearing

Whole circle Bearing

• This is the standard way of defining a bearing in surveying practice. The whole circle bearing of a line AB defined as the clockwise angle from 00 to 3600 at A between the direction to North and the direction to B.

Take the Bearing

• Whole circle Bearing

Quadrantal (Reduced) Bearing

• The reduced bearing of a line is define as the angle lying between 00 to 900 between the direction to North or south and  the direction of the line.
• The East and West directions are never used as reference lines but nevertheless are indicated since they  indicate the direction, either East or West, of the line from grid  North.

Quadrantal (Reduced) Bearing

Chain Surveying - Stepping

Measuring Up the hill and down the 

Ranging a line

• When two stations A and B separated by a considerable distance are selected and it is required to fix an intermediate point in between so that the same should lie in a straight line, the process is called “Ranging a line”.
• “The process of establishing intermediate point on a straight line between two end points is known as ranging”

There are two types of ranging.

• Direct Ranging:  It is done when two ends of survey line are intervisible.  This can be done either by eye or line ranger (optical instrument).
• Indirect Ranging:  It is called as reciprocal ranging.  It is done when two end points are too far or not intervisible due to obstruction.

Methods of Ranging

1. Ranging over a level ground (Direct ranging )
2. Ranging over a hill (Indirect ranging )

3.Ranging across a valley(Direct ranging)

• 1. Select two end points A  and  B which are far apart as shown in Figure and erect two ranging rods.
• 2. Select two intermediate points C and D very near to chain line such that from C, both D, and B are visible and from D, both C, and A are visible. 
• 3. Place two surveyors with ranging rods at both C and D.
• 4. The surveyor at C then directs another surveyor at D to move to D position in line with CB.
• 5. The surveyor at D then directs surveyor at C to move to C in line with CA
• 6. The above process is repeated till the points C  and  D  are located in a straight line that the person at C finds a person at D in line with CB and a person at D finds a person at C in line with DA.

OBSTACLE SURVEYING

• Types

1. Which can be seen across and can be chained by deviating on one or the other  Side
2. Which cannot be seen across but which can be chained by deviating to one or the  other side    
3. Which can be seen across but cannot be chained across (Across the river)

• Type 1- Low building,

•Select point C on chain and any other point E away from obstruction and measure CE.

•On EC set a right angle ED to have D on the chain line

•CD can be measured using Pythagoras law

Select any point C & D on chain line and form a triangle CKD Measure CK & DK Prolong CK & DK to G and F, making CK=KG & DK=KF Join FG Then FG=CD (CKD & KFG are congruent triangles)

Type 1- Bend of a river

Booking (recording )the survey data

Booking should carried out in the field book itself  using a field book. The pages approximately 150 x 100mm, each page is rule up the center with coloured lines about 15mm apart to represent the chain line and booking  start at the bottom of the page.

Points to be noted while surveying

• After preliminary reconnaissance of the site, make a sketch showing the location of the chosen station and chain line.
• Take the bearing from north at least one of the line.
• Take enough measurement

The principle features involved in booking – the lines, offsets, etc

• Begin each chain line at the bottom of fresh page
• Take plenty of room and make no attempt to scale in the bookings
• overstress any small irregularities, which are capable of being plotted
• Clear sketch of all details.
• Booking systematically starting with the side having more details (take more offsets)

PLOTTING OF A CHAIN SURVEY

• 1. Before commencement of plotting on drawing sheet, a suitable scale should be selected based on the linear measurements and space available on the drawing sheet  (A1 size:  594 mm  x  841  mm).
• 2. Convert ground measurements into plan distances in the field note book as per scale selected.
• 3. Fix the drawing sheet to the drawing board with the help of clamps or pins so that to edge of paper is parallel to the crony edge of the square when tee square head is kept against the sliding edge of divulging board.

PLOTTING OF A CHAIN SURVEY

• 4. Draw the border lines on the drawing sheet with 4 cm as left margin and 2.5 cm as the margin of the remaining sides.  Draw the rectangular box in right hand corner of drawing sheet for writing personal information.
• 5. The survey should be plotted facing north direction only.
• Lettering in Drawing Sheet:
• 1. Any  writing within drawing sheet should be with pencil and scale only.  No free hand writing is allowed.
• 2. Gothic plain style of English alphabets and numerals with vertical or slanting at 70º should be used.
• 3. Main title of the plotting should be written with the letter of 10 x 10 mm size on top of the drawing sheet.
• 4. Scale should be written with letter size of 7.5  x  7.5 mm below the main title (Eg:  SCALE: 1   cm   =   10  m)
• 5. The remaining writing on drawing sheet like distances, units, etc., should be done with letter size of  5  x  5 mm  only.
• 6. North line must be written vertically on top right side corner of drawing paper.  

Errors in chaining and their corrections.

Three types of errors.

• 1 .Mistakes
• 2 .Systematic or cumulative errors
• 3 . Random or accidental errors

corrections

1 .Mistakes

Misreads and forgotten to record data.

2 .Systematic or cumulative errors

(a) Incorrect length of the chain (Because of damage and wear) The error of the chain length could be rectified as applying following equation.

Correct length of chain = ( Measured length x length of chain used ) Length of standard

 A line was measured as 45.80 m with a chain 20.20 m long. What was the true length (TL) of the line?

TL 46.258m

corrections.

( b) Due to the slop of the surveying land

 All measurements must either be horizontal plane or be corrected to give the projection on this plain. Lines chained on sloping land must be longer than lines chained on the flat, and if the slope is excessive a correction must be applied.

corrections

There are two methods

1. Stepping
2. Measuring along the slop

This method is applicable where the ground runs in long regular slop. Then it could be corrected with measuring ground slop.

Correct length= Measured length x Cos ά

Cos ά = angle of the slope

corrections

3 . Random or accidental errors

• This may happens due to the lack of perfection in human eye and the method of using equipments.

Plane table surveying

• Technique by which the angles or directions between survey stations or detail points are drawn directly on to a portable drawing board in the field. 
• The survey is drawn directly on to a sheet of paper

PLANE TABLE SURVEYING

• Plane Tabling is a graphical method of surveying in which the field work and plotting are done simultaneously.
• Useful to fill in details between stations fixed by triangulation or theodolite traversing.
• Particularly adapted for small scale or medium scale mapping  in which great accuracy in detail is not required.
• The plane table consists essentially of:

1. A drawing board mounted on a tripod and 2. A straight edge called an alidade.

Equipments

• The plane table
• The alidade
• Spirit level
• Trough compass
• A plumbob & plumbing fork
• Drawing paper

SPIRIT LEVEL

• It consists of a small metal tube which contains a small bubble.
• The spirit level may also be circular but its base must be flat so that it can be laid on the table.
• The table is truly level when the bubble remains central all over the table.

Methods

• Radiation method
• Intersection method
• Traversing Method

Radiation Method

• The plane table is set up on convenient station.
• X and series of rays should be drawn through X towards the point (A, B, C, D…….) to be surveyed.
• The real lengths of XA XB, etc are measured using a measuring tape and drawn the plan using those values into an appropriate scale in the same paper.

Intersection Method

• The basic procedure in this method consists of taking sights on to an object with the table, correctly oriented at too separate station.
• Rays drawn on the board along these sight lines must intersect at the plotted of the object.
• In two stations A and B have being establish on the  ground at a known distance apart (the base line).

Traversing method

TRAVERSING METHOD

Traversing method

• Let us consider the stations P, Q, R and S which are to plotted by method of traversing.
• Stations are to be chosen in such a way that adjoining stations are visible.
• First, the plane table is to be set at station P and then plotted as p.
• With the alidade pivoted at p, draw the rays to Q and S. Distances PQ and PS are measured and plotted on the respective rays, pq and ps respectively.

Traversing method

• The plane table is then shifted to station Q, get it set and then oriented by back sighting to station P. With the alidade pivoted at q, draw a ray to R.
• Distance QR is measured and plotted on the ray as qr. In this way, plane table is shifted to stations R and S and corresponding rays are drawn to obtain the plotting of the traverse pqrs.
• Check lines. To check the accuracy of the plane table traverse, a few check lines are taken by sighting back to some preceding station

ADVANTAGES OF PLANE TABLING

1. It is most suitable for preparing small-scale maps.
2. It is most rapid.
3. The field book is not necessary as plotting is done in the field concurrently with the field work, and hence the mistakes in booking the field notes are avoided.
4. The surveyor can compare the plotted work with the actual features of the area surveyed and thus can ascertain if it represents them properly.
5. It is particularly advantageous in magnetic areas where compass survey is not reliable.
6. It is less costly than a theodolite survey. vii) No great skill is required to prepare a satisfactory map.

DISADVANTAGES OF PLANE TABLING

1. It is not suitable for work in a wet climate.
2. It is heavy, cumbersome and awkward to carry.
3. There are several accessories to be carried, and, therefore, they are likely to be lost.
4. It is not intended for accurate work.
5. If the survey is to be replotted to a different scale or quantities are to be computed, it is a great inconvenience in absence of the field notes.