What is Surveying?
The art of making measurements of the relative positions of natural and man-made features on the Earth’s surface, and the presentation of this information either graphically or numerically.
The work of the surveyor consists of 5 phases:
1. Decision Making – selecting method, equipment and final point locations.
2. Fieldwork & Data Collection – making measurements and recording data in the field.
3. Computing & Data Processing – preparing calculations based upon the recorded data to determine locations in a usable form.
4. Mapping or Data Representation – plotting data to produce a map, plot, or chart in the proper form.
5. Stakeout – locating and establishing monuments or stakes in the proper locations in the field.
Object of Surveying
The primary object of survey is the preparation of plan of estate or buildings roads, railways, pipelines, canals, etc. Or to measure area of field, state, nation.
Object of geodetic surveying is to determine precise positions on the surface of the earth of widely distant points.
Uses of Surveying
To prepare a topographical map this shows the hills, valley, rivers, villages, town, etc, of a country.
To prepare a cadastral map showing the boundaries of fields houses, and other properties.
To prepare an engineering map to show details like roads, railways, canals, etc.
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To prepare military map showing roads and railways, communication with different parts of country.
To prepare contour map and to determine capacity of a reservoirs and ton find the best possible route for roads, railways etc.
To prepare archeological map including places where ancient relics exist.
To prepare a geological map showing areas including underground resources
Types of Surveying (Classification)
A. Primary Classification or Primary Division :
1. Plane Surveying
The shape of the earth is spherical. Thus the surface is obviously curved. But in plane surveying the curvature of earth is not taken into account. This is because plane surveying is carried out over a small area, so the surface of the earth is considered as a plane. The degree of accuracy required in this type of surveying is completely low. Plane surveying is done on an area of less than 250 sq.km.
2. Geodetic surveying
In geodetic surveying the curvature of the earth is taken into consideration. It is extended over a large area greater than 250 sq.km. The line joining any two points considered as a curved line. Very refined methods and instruments are used in this type of surveying. In this method very high precision or accuracy is required.
B. Secondary Classification
Survey can be classified on different bases:
1. Based on instrument:
Chain Survey
compass survey
Plane Table survey
Theodolite survey
Tacheometric Survey
Photographic survey
2. Based on methods:
Triangulation Survey
Traverse Survey
3. Based on Objects:
Geological survey
Mine survey
Archeological Survey
Military survey
4. Based on nature of field:
Land Survey
Marine survey
Astronomical survey
Other Types of Surveys:
1. Photogrammetry – mapping utilizing data obtained by camera or other sensors carried in airplanes or satellites.
2. Boundary Surveying – establishing property corners, boundaries, and areas of land parcels.
3. Control Surveying – establish a network of horizontal and vertical monuments that serve as a reference framework for other survey projects.
4. Engineering Surveying – providing points and elevations for the building Civil Engineering projects.
5. Topographic Surveying – collecting data and preparing maps showing the locations of natural man-made features and elevations of points of the ground for multiple uses.
6. Route Surveys – topographic and other surveys for long – narrow projects associated with Civil Engineering projects.
Highways, railroads, pipelines, and transmission lines.
7. Hydrographic Surveying – mapping of shorelines and the bottom of bodies of water.
Also known as bathymetric surveying.
Brief History of Surveying:
18th & 19th Century in the New World: the need for mapping and marking land claims caused extensive surveying, especially by the English.
1785: United Stated began extensive surveys of public lands into one mile square sections
30 states surveyed under the U.S. Public Land System (also called the Rectangular System)
1807: United States Geological Survey founded to establish an accurate control network and mapping
Famous American Surveyors: George Washington, Thomas Jefferson, George Rogers Clark, Abe Lincoln and many more.
20th Century and Beyond: As technology advanced, population increased, and land value caused development of licensure for surveyors in all states.
Educational requirements for licensure began in the early 1990’s
Capable of electronic distance measurement, positioning using global positioning systems, construction machine control, and lidar (scanning) mapping
Involvement in rebuilding of the infrastructure and geographic information systems (GIS)
Shortage of licensed professionals is projected well into the 21st century
Measurement of Distance
Linear measurement is the basis of all surveying and even though angles may be read precisely, the length of at least one line in a tract must be measured to supplement the angles in locating points.
Old surveys were often measured using a Surveyors Chain. These were literally chains made up of 100 links. Each Chain was 66 feet long. Each link was 0.666 of a foot.
Units of Measurement
There are two main measuring systems:
English system and Metric system (SI units).
- All countries will change to Metric system.
- Angles are measured by: Degrees, minutes and seconds.
- 1 revolution = 360 degrees, 1 degree = 60 minutes and 1 minutes = 60 seconds.
Methods of Measuring Distance
Direct Method of Measuring Distance:
1. Pacing: Where approximate result is required, distance may be determined by pacing. This method is used for reconnaissance survey, for preparation of military plans. Also used for approximate checking distance. The method consists of walking over a line and counting the number of paces (80cm) the required distance may be obtained by multiplying the number of paces by the average length of pace.
2. Passometer:
It is a pocket instrument. It automatically records the number of paces. It should be carried vertically, in waistcoat pocket or suspended from a button. The mechanism being operated by motion and strain of the body.
3. Pedometer:
It is similar to passometer. But it registers the distance walked by the persons carrying it. The distance is read by means of an indicator. It is fitted with a stud or knob, which when pressed release indicator to zero, it may be carried in the same way as the passometer.
4. Odometer:
It measures the distance approximately. It can be attached to the wheel of any vehicle, such as carriage, cart bicycle, etc. It registers the number of revolution of the wheel. Knowing the circumference of the wheel, the distance traversed may be obtained by multiplying the number of revolutions. By the circumference of the wheel
5. Speedometer:
The Speedometer of an automobile may be used to measure distances approximately. It gives better results than pacing, provided the route is smooth.
The Speedometer of an automobile may be used to measure distances approximately. It gives better results than pacing, provided the route is smooth.
6. Perambulator:
It can measure distance rapidly. It consist a single wheel provided with forks and a handle. It is wheeled along the line, the length of which is desired. The distance traversed is automatically registered on the dial. The reading approximates on rough ground.
It can measure distance rapidly. It consist a single wheel provided with forks and a handle. It is wheeled along the line, the length of which is desired. The distance traversed is automatically registered on the dial. The reading approximates on rough ground.
7. Judging distance:
This is very rough method of determining distance. It is used reconnaissance survey.
8. Time Measurement:
Distance is roughly determined by time intervals of travel. Knowing the average time per km for a person at walk or a horse, the distance traversed may be easily obtained.
9. Chaining:
Measuring distance with chain or rope is the most accurate and common method, called as chaining. For work of ordinary precision a chain is used. Where great accuracy is required, a steel tape is used.
Measuring distance with chain or rope is the most accurate and common method, called as chaining. For work of ordinary precision a chain is used. Where great accuracy is required, a steel tape is used.
Measurement of Distance
Taping: applying the known length of a graduated tape directly to a line a number of times.
2 Problems exist in Taping:
Measuring the distance between two existing points
Laying out a known distance with only the starting point in place
Types of Chains and Tapes
Before the ability to make steel rods and bands, sticks were cut into lengths of 16.5’ (Rod) and they were laid end to end to measure.
Gunter’s Chain
66’ long with 100 link w/each link being 7.92 inches or 0.66 feet long.
Developed by Edmund Gunter in 1600’s in England and made with individual wires with a loop at each end connected
Engineer’s Chain
Same construction as Gunter’s Chain, but each link is 1.0’ long and was used for engineering projects
Surveyor’s and Engineer’s Tapes
Made of ¼” to 3/8” wide steel tapes in 100’; 200’; 300’ lengths
Invar Tapes
Made of special nickel steel to reduce length variations due to temperature changes
The tapes are extremely brittle and expensive
Used most of the time for standard comparison of tapes
Cloth, Fiberglass, and PVC Tapes:
Lower accuracy and stored on reels. Used for measurement of 0.1’ accuracy requirements
Taping (Field Process)
Accessories
Chaining Pins – set of 11, used to mark the tape lengths
Hand Level – used to determine required plumbing height
Plumb Bob – used to transfer the mark from the tape to ground
Tension Handle – used to maintain correct tension on tape
Steps involved in taping:
Laying out a known distance with only the starting point in placeLining in – shortest distance between two points is a straight line.
Applying tension – rear chain is anchor and head chain applies required tension.
Plumbing – horizontal distance requires tape to be horizontal.
Marking tape lengths – each application of the tape requires marking using chaining pins to obtain total length.
Reading the tape – the graduated tape must be read correctly.
Recording the distance – the total length must be reported and recorded correctly.
procedure:
The line to be taped should be marked at both ends
Keeps measurement on line
Rear chain person should keep the head chain person on line
1’ of line error/100’ = 0.01’ error in length
Applying Tension
Rear chainman is anchor and should hold 100’ mark over point
Tension is applied by head chain person – normally 12 to 30 pounds of pull
Tapes are standardized at 12 lbs., but greater is utilized to compensate for sag
Plumbing
One end of tape is raised to maintain a horizontal measuring plane. ONLY one end is elevated
This allows measurements to be made on uneven ground
If a high spot exists in center, “break” tape by measuring to the top and then move forward to complete the distance
Taping Error:
Instrumental Error – a tape may have different length due to defect in manufacture or repair or as the result of kinks
Natural Error – length of tape varies from normal due to temperature, wind and weight of tape (sag)
Personal Error – tape person may be careless in setting pins, reading the tape, or manipulating the equipment
Instrumental and natural error can be corrected mathematically, but personal error can only be corrected by remeasure.
When a tape is obtained, it should either be standardized or checked against a standard.
Tapes standardized at National Bureau of Standards in Maryland
Standardized at 68 degrees F and 12 lbs. tension fully supported.
Tape Error Correction
Measuring between two existing points:
If a tape is long, the distance will be short, thus any correction must be added
If tape is short, the distance will be long, thus any correction must be subtracted
If you :are setting or establishing a point, the above rule is reversed.
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Nice post
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