Surveying is the process of measuring angles and distances on the ground to plot them precisely on a map. Read on to find out more about surveying and its principles.
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see also: Chain surveying technique and mistakes to avoid
Surveying: What is it?
Surveying is the science and art of taking all necessary measurements to identify the relative location of points or physical and cultural elements above, on, or under the surface of the earth, and to display them in a useful manner. The theodolite, compass, auto-level, chains, tapes, levelling staff, total station, etc., are all essential pieces of surveying equipment.
Surveying includes both: the time spent in the field and in the office. This is because all necessary distance, angle, direction, elevation, location, area, and volume measurements are obtained in the field and then calculated back at the office.
Surveying: Purpose
Surveying is done to produce a map that depicts the relative locations of the various features on the surface of the earth. The map is created to a scale that seems appropriate. It illustrates the physical attributes of a nation, such as its cities, towns, highways, railroads, rivers, and other natural features. In addition, various technical developments, such as roads, trains, irrigation canals, and so on, are shown in minute detail on maps.
Surveying: Importance
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Working from the whole to the parts
- As implied by the term, the survey must be conducted from whole to part. This indicates that before beginning the process of surveying an area, a system of control points must first be built in such a way that it provides coverage of the whole region with a greater degree of accuracy.
- After this step, a reduced degree of accuracy is used in the process of establishing the remaining minor control points and details.
- The most important aspect of adhering to this approach is avoiding the unnecessary accumulation of mistakes so that you can better manage and pinpoint the more inconsequential ones.
- If the survey is conducted from part to whole, the error magnitudes would be quite significant.
- This principle must be followed to successfully locate international boundaries, property boundaries, and other types of boundaries.
Location of point by measurement from two points of reference
According to this principle, the relative position of the desired points to be surveyed must be determined by measuring from at least two (ideally three) points of reference, with the understanding that the locations of the reference points have already been determined in advance.
Consistency of work
The notion of maintaining consistency in one’s work is another essential aspect of surveying. To achieve the degree of accuracy that is required, it is important to highlight that maintaining consistency in the approach, instrument, reading, and notation of observations, etc., is helpful.
Independent check
According to this principle, every measurement that is made in the field must be re-checked by adopting a proper technique of independent field testing and observations. This is done to ensure that any error if it is there, is not overlooked without being brought to light.
Precision required
Following this principle of surveying, the technique and instrument that are used for the survey activity must be chosen appropriately in light of the needed level of precision.
Surveying: Method of surveying employed in the field of civil engineering
Plane surveying
- The surveying of planes is carried out not only by official organisations but also by commercial firms.
- It refers to the method of surveying in which the average surface of the earth is regarded as a plane rather than the spheroidal form of the earth is taken into consideration.
- When the area to be surveyed is less than 250 km², an aerial survey is carried out.
Geodetic surveying
- The country’s survey department is in charge of carrying out the geodetic survey.
- It refers to the method of surveying in which the spherical outlines of the earth are taken into consideration.
- The purpose of a geodetic survey is to ascertain the exact location, on the surface of the earth, of a network of points that are spread out across a large area and that come together to create control stations to which other surveys with varying degrees of accuracy might refer.
- It is conducted when the land area reaches over 250 km².
Surveying: Secondary classification of surveying based on the nature of the survey
A survey’s classification can be determined by its field, its subject, and its methods.
Topographical surveys
They are carried out to establish the location of natural elements of an area, such as rivers, streams, hills, and other geographical features, as well as constructed structures, such as highways and canals in the region. These kinds of surveys are done to create maps, which are known as “topo-sheets”, after they are finished.
Hydrographic survey
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The M.S.L. (mean sea level), the water spread area, the depth of water bodies, the velocity of flow in streams, and the cross-section area of flow are all things that can be determined with the use of hydrographic surveying.
Astronomical survey
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The purpose of the Astronomical Survey is to ascertain the precise geographical position of every given place on the earth’s surface. The survey entails looking up and making observations of things like stars and other celestial entities.
Engineering survey
When it is necessary to gather adequate data for the purpose of planning and developing engineering works such as roads, bridges, and reservoirs, this sort of survey is carried out. Examples of such works are roads, bridges, and reservoirs.
Archaeological survey
The purpose of this kind of survey is to acquire information about locations that are significant from an archaeological standpoint and to excavate artefacts that date back to ancient times.
Photographic survey
In this sort of survey, information is gathered by utilising a camera to take images at various spots around the area being surveyed.
Aerial survey
Taking images of wide swaths of terrain from above using an aeroplane is the method of data collection used in this sort of survey.
Reconnaissance survey
During this form of survey, data is gathered by making notations of physical observations and taking a few measurements using simple survey devices.
Surveying: Classifiaction based on the type of instruments
Chain surveying
- The most fundamental and traditional method of surveying is called chain surveying. The method of triangulation is used throughout the chain survey process.
- Many smaller triangles are created out of the overall region that has to be surveyed.
- Angles of triangles must not be less than 30 degrees and larger than 120 degrees. Equilateral triangles are believed to be perfect triangles.
- Tie line and check line control ensure that the task is done accurately rather than using angle measurements.
- This approach works well when the terrain is relatively flat and undulating just slightly, and the area that has to be surveyed is not very large.
Compass surveying
- The principle of traversing is used in compass surveying. Making triangles is not a prerequisite for using this procedure in any way.
- The magnetic bearing of the line is determined with the help of a prismatic compass, and the distance is determined with the help of a chain.
- A compass is used to construct a set of connecting lines, and a chain is used to measure distances between points.
- When locating interior features, an offset from the main survey lines is used.
- They are appropriate for wide-area surveys crammed with numerous details. It can be used to survey a river channel.
Plane table surveying
- Parallelism is the fundamental idea behind plane table surveying.
- They are placed immediately on the paper, along with their positions concerning one another.
- The rays are traced out, beginning at the station and ending at the item on the ground.
- The table is positioned at each subsequent station in a manner that is parallel to the location of the table at the most recent station.
- They are advised for use in situations where a high level of precision is not needed since they are mainly ideal for filling interior details.
Theodolite surveying
The theodolite is primarily used as an instrument for the purpose of precise measuring of both horizontal and vertical angles. They have a high degree of accuracy for measuring angles up to 10 or 20 inches. Measurements such as these can be taken using a theodolite:
- Horizontal angles
- Vertical angles
- Deflection angle
- Magnetic bearing
- The horizontal distance between two points
- Vertical height between two points
- Difference in elevation
In modern times, the theodolite has been largely superseded and replaced by the use of a total station, which can do the same operation with far less effort and more precise results.
Tacheometric surveying
- A tacheometer is a subfield of surveying in which horizontal and vertical distances are measured by using a device called a tachometer to make angular measurements and then using those observations to calculate the distances.
- The tacheometer is only a transit theodolite that has had a stadia diaphragm and an analytic lens added to it. In this kind of poll, chaining is not necessary at all.
- The concept of the tacheometer is derived from the fact that an isosceles triangle has a feature known as the “constant ratio,” which states that the distance of the base from the apex of the triangle and the length of the base remains unchanged.
Photographic surveying
The method of taking photographs at a variety of angles is the foundation of the photographic survey. This allows for the preparation of topographic data at a relatively high rate of speed. There are two primary approaches to photographic surveying:
Terrestrial or ground photogrammetry
Terrestrial photogrammetry is the process of creating maps using ground images taken at various locations around the earth’s surface for the goal of making measurements.
Aerial photogrammetry
Aerial photogrammetry involves taking photographs of terrain from a moving aircraft, such as a plane or helicopter.
Photogrammetry comprises two key areas of speciality.
- Metrical photogrammetry: Metrical photogrammetry is of primary importance to surveyors. It can be used to estimate things like distances, altitudes, areas, volumes, and so on to compile topographic maps from measurements recorded on images.
- Interpretive photogrammetry: The process of determining the importance of items based on their photographic images is known as interpretive photogrammetry. When attempting to identify an item, important considerations include its form, size, pattern, and shadow.
Surveying: Uses
The following is a list of the many applications that make use of surveying:
- To create a topographical map of a nation that details its many features, including its mountains, valleys, and rivers, as well as its cities, villages, and woods.
- To create a cadastral map that details the locations of various properties, including fields, homes, and other buildings.
- To create an engineering map that depicts the specifics of various engineering works, including roads, trains, reservoirs, irrigation canals, and other similar features.
- To create a military map that details the roadways and rail lines that connect various regions of a nation to one another. A map of this kind also illustrates the many strategic sites that are significant for the protection of a nation.
- To assess the capacity of a reservoir by creating a contour map and to locate the most efficient path for roads, trains, and other forms of transportation by doing so.
- To compile a geological map illustrating the regions in question, including any subterranean resources.
- To create a map of the archaeological site, including locations on the map where ancient artefacts could be found.
FAQs
What is the primary objective of surveying?
The primary objective of surveying is to create a map or plan that depicts a region on a horizontal plane.
What is the survey's first principle?
Following the first concept, the whole region is surrounded by primary stations (i.e., controlling stations) and primary survey lines (i.e. controlling lines). The area is then subdivided into many sections by constructing well-formed triangles.
What is the difference between surveying and levelling?
Surveying refers to the measuring of horizontal distances using specialised instruments. It determines the horizontal elevation of the fixed line. On the other side, Levelling consists of adaptable equipment for measuring vertical distance
Which are the two most common forms of surveying error?
Errors can be classified as either systematic or random. If the surveyor wants to do a good job, he or she has to know the difference between these two types of mistakes. A survey's accuracy can be drastically impacted by variables, including the quality of the surveying tools utilised, the methodology used, and the surrounding environment.
In a survey, what are the three most common types of error?
Coverage error, sampling error, and nonresponse error are three common types of error in survey-based estimations that must be accounted for in the decomposition.
What is the definition of a natural error in surveying?
Natural error in surveying can result from fluctuations in natural phenomena like temperature, humidity, gravity, wind, refraction, and magnetic declination. If they are not observed correctly during measurement, the findings will be inaccurate.