GUJARAT TECHNOLOGICAL UNIVERSITY
Unit – 4
INTRODUCTION TO SURVEYING AND LEVELLING
Content
Principles of survey
The two principles are:
1. LOCATION OF A POINT BY MEASUREMENT FROM TWO POINTS OF REFERENCE:
The relative positions of the points to be surveyed should be located by taking measurement from at least two points of reference. Points of reference are points whose position is already fixed
2. SECOND PRINCIPLE IS TO WORK FROM WHOLE TO PART:
It is very essential to establish first a system of control points and to fix them with higher precision. Minor control points can be established by less precise methods and the details can be located using these minor control points by running minor traverses.
CLASSIFICATION OF SURVEYING
Generally, surveying is divided into two major categories: plane and geodetic surveying
- PLANE SURVEYING
PLANE SURVEYING is a process of surveying in which the portion of the earth being surveyed is considered a plane. The term is used to designate survey work in which the distances or areas involved are small enough that the curvature of the earth can be disregarded without significant error. In general, the term of limited extent. For small areas, precise results may be obtained with plane surveying methods, but the accuracy and precision of such results will decrease as the area surveyed increases in size. To make computations in plane surveying, you will use formulas of plane trigonometry, algebra, and analytical geometry.
2. GEODETIC SURVEYING
GEODETIC SURVEYING is a process of surveying in which the shape and size of the earth are considered. This type of survey is suited for large areas and long lines and is used to find the precise location of basic points needed for establishing control for other surveys. In geodetic surveys, the stations are normally long distances apart, and more precise instruments and surveying methods are required for this type of surveying than for plane surveying.
- TOPOGRAPHIC SURVEYS
The purpose of a TOPOGRAPHIC SURVEY is to gather survey data about the natural and man-made features of the land, as well as its elevations. From this information a three-dimensional map may be prepared. You may prepare the topographic map in the office after collecting the field data or prepare it right away in the field by plane table. The work usually consists of the following:
1. Establishing horizontal and vertical control that will serve as the framework of the survey
2. Determining enough horizontal location and elevation (usually called side shots) of ground points to provide enough data for plotting when the map is prepared
3. Locating natural and man-made features that may be required by the purpose of the survey
4. Computing distances, angles, and elevations
5. Drawing the topographic map
Topographic surveys are commonly identified with horizontal and/or vertical control of third-and lower-order accuracies.
ROUTE SURVEYS
The term route survey refers to surveys necessary for the location and construction of lines of transportation or communication that continue across country for some distance, such as highways, railroads, open-conduit systems, pipelines, and power lines. Generally, the preliminary survey for this work takes the form of a topographic survey. In the final stage, the work may consist of the following:
1. Locating the center line, usually marked by stakes at 100-ft intervals called stations
2. Determining elevations along and across the center line for plotting profile and cross sections
3. Plotting the profile and cross sections and fixing the grades
4. Computing the volumes of earthwork and preparing a mass diagram
5. Staking out the extremities for cuts and fills
6. Determining drainage areas to be used in the design of ditches and culverts
7. Laying out structures, such as bridges and culvert
8. Locating right-of-way boundaries, as well as staking out fence lines, if necessary
SPECIAL SURVEYS
SPECIAL SURVEYS are conducted for a specific purpose and with a special type of surveying equipment and methods. A brief discussion of some of the special surveys familiar to you follows.
- Land Surveys
LAND SURVEYS (sometimes called cadastral or property surveys) are conducted to establish the exact location, boundaries, or subdivision of a tract of land in any specified area. This type of survey requires professional registration in all states. Presently, land surveys generally consist of the following chores:
1. Establishing markers or monuments to define and thereby preserve the boundaries of land belonging to a private concern, a corporation, or the government.
2. Relocating markers or monuments legally established by original surveys. This requires examining previous survey records and retracing what was done. When some markers or monuments are missing, they are re-established following recognized procedures, using whatever information is available.
3. Rerunning old land survey lines to determine their lengths and directions. As a result of the high cost of land, old lines are re-measured to get more precise measurements.
4. Subdividing landed estates into parcels of predetermined sizes and shapes.
5. Calculating areas, distances, and directions and preparing the land map to portray the survey data so that it can be used as a permanent record. 6. Writing a technical description for deeds.
- Control Surveys
CONTROL SURVEYS provide "basic control" or horizontal and vertical positions of points to which supplementary surveys are adjusted. These types of surveys (sometimes termed and traverse stations and the elevations of bench marks. These control points are further used as References for hydro graphic surveys of the coastal waters; for topographic control; and for the control of many state, city, and private surveys.
Horizontal and vertical controls generated by land (geodetic) surveys provide coordinated position data for all surveyors. It is therefore necessary that these types of surveys use first-order and second-order accuracies.
- Hydrographic Surveys
HYDROGRAPHIC SURVEYS are made to acquire data required to chart and/or map shorelines and bottom depths of streams, rivers, lakes, reservoirs, and other larger bodies of water. This type of survey is also of general importance to navigation and to development of water resources for flood control, irrigation, electrical power, and water supply.
Linear measurement
Linear Measurements
The determination of the distance between two points on the surface of the earth is one of the basic operation of surveying. Measurement of horizontal distances or measuring linear measurement is required in chain surveying, traverse surveying and other types of surveying.
Methods of making linear measurements
Direct methods
In the direct method, the distance is actually measured during field work using a chain or a tape. This is the most commonly used method for linear measurements.
Optical methods
In the optical methods, principles of optics are used. The distance is not actually measured in field but it is computed indirectly. The instrument used for making observations is called tacheometer.
E.D.M methods
Electronic Distance Measuring (E.D.M) instruments have been developed quite recently.
These are practically replacing the measurement of distances using chains or tapes. There is a large variety of such instruments and depending upon the precision required the instruments should be used.
Linear Measurements
The determination of the distance between two points on the surface of the earth is one of the basic operation of surveying. Measurement of horizontal distances or measuring linear measurement is required in chain surveying, traverse surveying and other types of surveying.
Instruments used
Methods of making linear measurements
Direct methods
In the direct method, the distance is actually measured during field work using a chain or a tape. This is the most commonly used method for linear measurements.
Optical methods
In the optical methods, principles of optics are used. The distance is not actually measured in field but it is computed indirectly. The instrument used for making observations is called tacheometer.
E.D.M methods
Electronic Distance Measuring (E.D.M) instruments have been developed quite recently.
These are practically replacing the measurement of distances using chains or tapes. There is a large variety of such instruments and depending upon the precision required the instruments should be used.
Chain surveying
Chain surveying is that type of surveying in which only linear measurements made in the field.
Surveying is suitable for surveys of the small extent on open ground to secure data for an exact description of the boundaries of a piece of land or to take simple details.
The principle of chain survey or Chain Triangulation, as is sometimes called, is to provide a skeleton or framework consists of a number of connected triangles, as the triangle is the only simple draw that can be plotted from the lengths of its sides measured in the field book.
To good results in plotting, the framework should be consist of triangles which are as nearly equilateral as possible.
Principle of Chain Surveying
The principle of chain surveying is triangulation. This means that the area to survey is spilled into a number of small triangles which should be well-conditioned.
In chain surveying, the side of the triangles are measured directly from the field by chain or tape, and no angular measurements are used. Here, the check lines and tie lines control the accuracy of the given work.
It is noted that plotting triangles requires no angular measurements to be made if the three sides are known.
Error in chaining
Errors in chaining may be classified as:
(i) Personal errors
(ii) Compensating errors, and
(iii) Cumulating errors.
Personal Errors
Wrong reading, wrong recording, reading from wrong end of chain etc., are personal errors. These errors are serious errors and cannot be detected easily. Care should be taken to avoid such errors.
Compensating Errors
These errors may be sometimes positive and sometimes negative. Hence they are likely to get compensated when large number of readings are taken. The magnitude of such errors can be estimated by theory of probability. The following are the examples of such errors:
(i) Incorrect marking of the end of a chain.
(ii) Fractional part of chain may not be correct though total length is corrected.
(iii) Graduations in tape may not be exactly same throughout.
(iv) In the method of stepping while measuring sloping ground, plumbing may be crude.
Cumulative Errors
The errors, that occur always in the same direction are called cumulative errors. In each reading the error may be small, but when large number of measurements are made they may be considerable, since the error is always on one side. Examples of such errors are:
(i) Bad ranging
(ii) Bad straightening
(iii) Erroneous length of chain
(iv) Temperature variation
(v) Variation in applied pull
(vi) Non-horizontality
(vii) Sag in the chain, if suspended for measuring horizontal distance on a sloping ground.
Errors (i), (ii), (vi) and (vii) are always +ve since they make measured length more than actual.
Errors (iii), (iv) and (v) may be +ve or –ve.
Offset
The lateral measurement taken from an object to the chain line is known as ‘offset’. Offsets are taken to locate objects with reference to the chain line. They may be of two kinds.
1. Perpendicular offset and
2. Oblique offset.
Perpendicular offset: When the lateral measurements are taken perpendicular to the chain line, they are known as perpendicular offsets
Oblique offset: Any offset not perpendicular to the chain line is said to be oblique offset. Oblique offset taken when the objects are at the long distance from the chain line or when it is not possible to set up a right angle.
Ranging
Ranging is of two types
Direct Ranging
- The ranging in which intermediate ranging rods are placed in a straight line by direct observation from either end.
- Direct ranging is possible only when the end stations are inter visible.
Indirect Ranging
- The ranging in which intermediate points are interpolated by reciprocal ranging or running an auxiliary line.
- Indirect ranging is done where end points are not visible and the ground is high .
Compass-Instrument used
Prismatic compass
Prismatic compass is a portable magnetic compass which can be either used as a hand instrument or can be fitted on a tripod. It contains a prism which is used for accurate measurement of readings. The greatest advantage of this compass is both sighting and reading can be done simultaneously without changing the position.
The bearings are expressed in the following two ways:
- Whole circle bearings
- Quadrantal bearings
- Whole Circle Bearings:
The horizontal angle which a line makes with the north direction of the meridian measured in the clockwise direction and can value upto 360° i.e. the whole circle, is known as whole circle bearing (W.C.B.) of the line.
The prismatic compass measures the bearings of lines in the whole circle system.
B. Quadrantal Bearings:
The horizontal angle which a line makes with the north or south direction of the meridian whichever is nearer the line measured in the clockwise or counter clockwise direction towards east or west and can value up to 90° i.e. one quadrant of a circle is known as quadrantal bearing of the line.
The surveyor’s compass measures the bearings of lines in the quadrantal system.
Meridian, Bearing
Depending upon the meridian, there are four type of bearings they are as follows
1) True Bearing: The true bearing of a line is the horizontal angle between the true meridian and the survey line. The true bearing is measured from the true north in the clockwise direction.
2) Magnetic Bearing: the magnetic bearing of a line is the horizontal angle which the line makes with the magnetic north.
3) Grid Bearing: The grid bearing of a line is the horizontal angle which the line makes with the grid meridian.
4) Arbitrary Bearing: The arbitrary baring of a line is the horizontal angle which the line makes with the arbitrary meridian.
System Of Bearing
Bearings of lines may be calculated if bearing of one of the lines and the included angles measured clockwise between the various lines are given.
- Bearing of a line = given bearing + included angle.
The bearings of lines may be given in:
(i) The whole circle system, or
(ii) The quadrantal system.
Local attraction
Local attraction is the phenomenon by which the magnetic needle is constantly prevented to point towards the magnetic north at a place. This is because that these magnetic compass is influenced by other magnetic objects at that locality such as wires carrying electric current, rails, steel and iron structures, steel tapes etc.
The occurrence of local attraction can be detected by observing the difference between the fore and back bearings. If there is no influence of local attraction and other error, this difference will be 180. So we can then conclude that both stations are free from local attraction.
Levelling is defined as “an art of determining the relative height of different points on, above or below the surface
Principle of Levelling
The principle of levelling is to obtain horizontal line of sight with respect to which vertical distances of the points above or below this line of sight are found.
Object of levelling
- To Find the elevation of given point with respect to some assumed reference line called datum.
To establish point at required elevation respect to datum
Types of Levelling Instruments
According to the general arrangement of various parts, the levels may be classified as:
- Dumpy level,
- Wye level,
- Reversible level such as Cooke’s reversible level and Cushing’s level, and
- Tilting level.
1. Dumpy level.
- In the modern form of Dumpy level also called “solid Dumpy level”, the vertical spindle and the telescope are rigidly fixed so that the telescope can neither be rotated about its longitudinal axis nor removed from the supports.
- This levelling instrument is more stable when compared to others and retains its permanent adjustment for a long time.
2. Wye or Y level.
- In this instrument, the stage carries two “wye” supports in which the telescope is fixed.
- To the body of the telescope, two hanged collars of equal diameters are fixed. These collars rest on the “Wyes.”
- The telescope can be rotated about its longitudinal axis, or it can be taken out and placed end-for-end in the wyes.
- A clamp and a tangent screw are provided to facilitate accurate sighting of the objects. This is a very delicate instrument and consists of a large number of loose and open parts.
- Due to the reversibility of the telescope, the instrument may be more easily tested for permanent adjustments.
3. Cooke’s reversible level.
- This Levelling instrument combines the good features of both the Dumpy and the Wye levels.
- By loosening the screw, the telescope can be rotated about its longitudinal axis and can also be withdrawn from the sockets and placed end-for-end.
4. Cushing’s level.
- Cushing’s level is in that type of levelling instruments in which, the telescope is rigidly fixed in the collar as in a Dumpy Level.
- The two ends of the telescope barrel have equal sockets which can either received the objective or the eye-piece and diaphragm.
- Reversal of the line of collimation may be established by interchanging the objective and the eyepiece. The eye-piece can be rotated in its fitting.
5. Tilting Level.
- In the above four types of levelling instruments, the line of collimation is at the right angle to the vertical axis, if the instrument is in the permanent adjustment.
- Therefore, when the bubble is centered the line of collimation is made horizontal and the vertical axis is made truly vertical.
- In the tilting level, the telescope along with its bubble tube can be leveled by a micrometer screw without using the foot screws of the instrument, i.e., the line of collimation may be made horizontal independent of the vertical axis.
Introduction to contour
Contours
A contour is an imaginary line on the ground that passes through points having the same elevation.
Characteristics of contour lines:
- Contour lines are continuous.
- Contour lines are relatively parallel unless one of two conditions exists.
- A series of V-shape indicates a valley and the V’s point to higher elevation.
- A series U shape indicates a ridge. The U shapes will point to lower elevation.
- Evenly spaced lines indicate an area of uniform slope.
- A series of closed contours with increasing elevation indicates a hill and a series of closed contours with decreasing elevation indicates a depression.
- Closed contours may be identified with a +, hill, or -, depression.
- Closed contours may include hachure marks. Hachures are short lines perpendicular to the contour line. They point to lower elevation.
- The distance between contour lines indicates the steepness of the slope. The greater the distance between two contours the less the slope. The opposite is also true.
- Contours are perpendicular to the maximum slope.
- A different type of line should be used for contours of major elevations. Common practice is to identify the major elevations lines, or every fifth line, with a bolder, wider, line
Introduction to Theodolite
- Theodolite is used to measure the horizontal and vertical angles.
- Theodolite is more precise than magnetic compass.
- Magnetic compass measures the angle up to as accuracy of 30’.
- However a vernier theodolite measures the angles up to and accuracy of 10’’, 20”. There are variety of theodolite vernier, optic, electronic etc.
Introduction to Total Station
- The Total station is designed for measuring of slant distances, horizontal and vertical angles and elevations in topographic and geodetic works, tachometric surveys, as well as for solution of application geodetic tasks. The measurement results can be recorded into the internal memory and transferred to a personal computer interface.
- The basic properties are unsurpassed range, speed and accuracy of measurements. Total stations are developed in view of the maximal convenience of work of the user. High-efficiency electronic tachometers are intended for the decision
- It has the broad audience for sole of industrial problems.
- Angles and distances are measured from the total station to points under survey, and the coordinates (X, Y, and Z or northing, easting and elevation) of surveyed points relative to the total station position are calculated using trigonometry and triangulation.
- Data can be downloaded from the total station to a computer and application software used to compute results and generate a map of the surveyed area.
- A total station is an electronic/optical instrument used in modern surveying. It is also used by archaeologists to record excavations as well as by police, crime scene investigators, private accident Reconstructionists and insurance companies to take measurements of scenes. The total station is an electronic theodolite (transit) integrated with an electronic distance meter (EDM), plus internal data storage and/or external data collector.
- The purpose of any survey is to prepare maps, control points formed a basic requirement for the preparation of these maps.
- There are several numbers of methods like traverse, triangulation etc., to provide these control points.
- Whatever the method the provision of control points, includes the measurement of two entities( Distance and Angle).
- Again, distance can be measured by using various instruments like chain, tape.
Introduction to GPS, GIS & RS
GPS
Global Positioning Systems or GPS are used to find the exact location of things. Geographic Information Systems or GIS are used to record information on to maps. Both GPS and GIS are useful in managing land in the high country.
Uses of GPS
GPS has many uses, for example;
- Clock synchronization: The GPS time signals use highly accurate atomic clocks. This technology can be used for things like automatic updates of daylight saving times on cell phones
- Disaster relief and emergency services: Depend upon GPS for location
- Tracking a vehicle, person, pet or aircraft: Receivers provide continuous tracking and can provide an alert if the receiver leaves a set area. Pets can be chipped so they can be found if they become lost
- Geotagging: Applying location coordinates to digital objects such as photographs and other documents for purposes such as creating map overlays.
- Bus tour commentary: your location will determine what information is displayed about approaching points of interest
- Bus stops: to show how long the bus will take to arrive at a bus stop
- Navigation: e.g. Navman. The device uses voice activation to describe a preferred route based on the position of the receiver, the position of the destination and a street map
- Personal Locator Beacons (PLB): used to inform search and rescue authorities of your exact location in the event of an emergency
- Recreation: For example, geocaching and way marking
- Surveying: Surveyors use absolute locations to make maps and determine property boundaries
- Tectonics: enables fault motion measurement in earthquake
GIS
- Maps have come a long way since people first began drawings to show where they were. Modern maps are made using special software that combines lots of different sorts of information. This system of modern mapping is called GIS – Geographic Information Systems. GIS is used by groups such as city councils, that need access to data and need to be able to combine different data sets together. GIS gives people a picture of data that allows them to:
- Problem solve
- Write reports
- Track changes
- Make decisions
- Plan for the future e.g. which areas of the high country have completed tenure review
GIS requires four things:
- People: people who are trained in GIS
- Data: geospatial information (where things are located) is entered into the GIS software
- Software: GIS software analyses data and presents it in different ways for the user
- Hardware: includes hand held devices for collecting data and computers with GIS software
Data contained in a GIS system is stored in sets of data called ‘data sets’ in a database. Data sets can be selected, combined and presented as layers:
RS
Remote sensing is the process of acquiring information, detecting, analyzing, monitoring the physical characteristics of an area by recording it is reflected and emitted radiation energy without having any physical contact with the object under study. This is done by capturing the reflected radiation/energy.
Types of remote sensing
1. Active sensor
The sensor embodies within itself the source of illumination like a satellite equipped with a RADAR sensor. Active sensors throw their own energy to scan the object. RADAR and LiDAR are examples of active remote sensing which measure the time delay between emission and return.
2. Passive sensor
The sensors gather radiation that is emitted or reflected by the object or surrounding areas. Sunlight reflection is the most common source of radiation measured by passive sensors. Examples of passive remote sensors are photography, infrared, and radiometers. Passive sensors are more used because it provides great quality satellite imagery. The passive sensor is superior within the field of technical observation of the planet, such as Multispectral and Hyper spectral technology.
Remote Sensing Major Applications Area
Satellites play a huge role in the development of many technologies like world mapping, GPS, City planning, etc. Remote Sensing is one of the many innovations that were possible, thanks to the satellites roaming around the earth.
The primary application of remote sensing
Analyzing the condition of rural roads
Rural road conditions are now possible to be analyzed using various GIS technique and Remote Sensing techniques with an inch to inch accuracy. It saves a lot of time and money from transporters.
Creating a base map for visual reference
Nowadays many modern mapping technologies are based on Remote Sensing including Google maps, open street maps, Bing maps, NASA’s Globe view, etc.
Computing snow pack
Snow melt ratio can be easily understood by using Remote Sensing technology, NASA uses LIDAR along with a spectrometer in order to measure the absorption of sunlight.
Collecting earth’s pictures from space
Many space organization has a collection containing images of earth. Interesting patterns of earth’s geometry including atmosphere, oceans, land, etc can be seen in it. EO-1, Terra, and Lands at are used to collect this data.
- Controlling forest fires
Information acquired by satellites using Remote Sensing enables fire fighters to be dispatched on time and over correct locations so the damage from such fires can be decreased to minimal.
- Detecting land use and land cover
Remote Sensing technologies are used to determine various physical properties of land and also what it is being used for (land use).
- Estimating forest supplies
MODIS, AVHRR, and SPOT are regularly used to measure the increment/decrement in global forests since forests are the source of valuable materials such as paper, packaging, construction materials, etc.
- Locating construction and building alteration
Tax revenue agencies use satellite data in several countries including Greece, Athens, etc. They locate signs of wealth using this technology. Early in the year of 2013, there were 15000 swimming pools (unclaimed to steal taxes) in those countries.
- Figuring out fraud insurance claims
Many insurance companies use Lands at red and infrared channels to figure out vegetation growth in particular land. This information can be used to verify seeded crops and fight against crop insurance fraud.
- Observing climate changes
Satellites such as CERES, MODIS, AMSRE, TRMM, and MOPITT has made it possible to observe climate changes from up above the skies. It is also possible to compare past climate situation with the current one.
- Predicting potential landslides
Landslides cause noticeable death and wealth loss around the globe. INSAR uses inter ferometry remote sensing technique for providing an early warning regarding potential landslides.
