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Evolution in surveying Techniques

by Yashwant Singh


 
Definition

Surveying is the process of determining the relative position of natural and man-made features on or under the earth surface. The American Congress on Surveying and Mapping (ACSM), defines surveying as the science and art of making all essential measurements to determine the relative position of points or physical and cultural details above, on, or beneath the surface of the Earth, and to depict them in a usable form, or to establish the position of points or details.

 

Ancient surveying

Four thousand years ago, the concepts of math were basic, yet the Egyptians were able to achieve wonders. They used the predecessors of modern surveying instruments to engineer many feats, from canals to pyramids.  An ancient Egyptian survey crew used measuring ropes, plumb bobs, sighting instruments, and leveling instruments.

a) Rope Stretcher
According to ancient legend pictures found in Egyptian tombs show scribes and their assistants carrying ropes tied with equally-spaced knots. Speculation is that the ropes were used to create right triangles to establish boundaries after the yearly flooding of the Nile which helped build the pyramids.

 

b) Groma Surveying
The Groma or gruma was a Roman surveying instrument. It comprised a vertical staff with horizontal cross-pieces mounted at right angles on a bracket. Each cross piece had a plumb line hanging vertically at each end. It was used to survey straight lines and right angles, hence squares or rectangles. They were stabilized on the high ground and pointed in the direction it was going to be used.


 
The Romans recognized land surveying as a profession. They established the basic measurements under which the Roman Empire was divided, such as a tax register of conquered lands. Roman surveyors were known as Gromatici.

Even after centuries passed, the purpose of surveying has remained somewhat the same: establishing boundaries, creating maps for navigation and developing the land. While the purposes of surveying remain constant, the tools used to accomplish them have evolved drastically with human advancement. Because land surveying establishes boundaries and mapping, it is an essential part of the land development and land ownership. Land mapping and measuring can date back to the ancient Egyptians and has paved the way for today’s surveying techniques and methods.

Modern Surveying

a) Plane Table
This surveying device provides a solid and level surface on which we can make field drawings, charts, and maps. This became a very popular instrument of surveying. It allows the use of graphical methods rather than mathematical methods which makes it easier to use by a less educated person too. The plane table consists of a smooth table surface mounted on a strong base. Bubble levels in a horizontal plane is used to level the table precisely.
 

b) Gunter's Chain
Gunter's chain or the surveyor's chain is a device used in measuring the distance for a land survey. This was introduced by Edmund Gunterlong before the development of theodolite and other sophisticated equipment. 66 feet long chain divided into 100 links which are marked by 10 brass rings. Each link is 7.92 inches long. One acre is measured by ten square chains in Gunter's system.

 

c) Theodolite
With the further development of surveying tools, the measurement of angles in horizontal and vertical planes was much needed and the answer came in the form of the theodolite. This has also been adopted for meteorology and rocket launch. The modern theodolite consists of a movable telescope mounted on two perpendicular axis. When the telescope is pointed at a target object, the angle of each of these axes can be measured with great precision, typically to milliradian or seconds of an arc.
 

d) Triangulation Method
This is the process of determining the location of a point by forming triangles to it from known points. This involves only angle measurement rather than measuring distance. Optical 3D measuring systems use this principle as well in order to determine the spatial dimensions and the geometry of an item. Basically, the configuration consists of two sensors observing the item. 

Triangulation today is used for many purposes, including surveying, navigation, metrology, astrometry, binocular vision, model rocketry and gun direction of weapons.


 
20th century

Even after the replacement of ropes and chains surveyors still faced the problem of accurate measurement of long distances.

A) Tellurometer
It was the first successful microwave Electronic Distance Measurement (EDM). The Tellurometer emits an electronic wave: the remote station reradiates the incoming wave in a similar wave of more complex modulation, and the resulting phase shift is a measure of the distance traveled. The results appear on a cathode ray tube. This instrument penetrates haze and mist in daylight or darkness and has a normal range of 30–50 km but can extend up to 70 km.

 

B) Total Station
In the 1970s the first instruments combining angle and distance measurement appeared, which came to be known as total stations. This brings accuracy and speed in the measurement. Major advances were tilt compensators, data recorders, and onboard calculation programs.


 
C) Global Positioning System
The US Air Force launched the first prototype satellites of the Global Positioning System (GPS) in 1978. GPS uses a larger constellation of satellites and improved signal transmission to provide more accuracy. Early GPS observations required several hours of observations by a static receiver to reach survey accuracy requirements. Recent improvements to both satellites and receivers allow Real Time Kinematic (RTK) surveying. RTK surveys get high-accuracy measurements by using a fixed base station and a second roving antenna. The position of the roving antenna can be tracked.
 

21st century

In today's life theodolite, Total Station and RTK GPS are the primary methods in use. LiDAR is also being used in topographic surveying today. UAV technology along with photogrammetry image processing is also gaining popularity. If you have a small parcel of land, you don’t want to go through the expense of contracting plane and pilot to map it. Aerial surveying drones are the perfect solution.

                                  Comparing Real-Time Kinematic (RTK) and Post Processed Kinematic (PPK)

Real-Time Kinematic (RTK) is a GPS correction technology that provides real-time corrections to location data when the survey drone is capturing photos of a site.

Post Processed Kinematic (PPK), another GPS correction technology technique that works to correct location data, except in the cloud after the drone data has been captured and uploaded.

Basically, the main difference between the two is when this positional correcting takes place. RTK corrects during the flight, and PPK corrects after the flight. Both these technologies are very similar, however, PPK has a decisive advantage — because of its robustness and consistency. PPK drones offer more flexibility in terms of the actual flight of the survey drone, which means you have more freedom of how and where the drone is deployed. In contrast, RTK drones require a very specific base station and other pieces of equipment that work together in order to process data in real-time. Secondly, with PPK drones can refer to previous and future data relative to the current flight, which creates greater dependability. Having this ability ensures the drone is always on track with the flight.


SATPALDA is a privately owned company and a leading provider of satellite imagery and GeoSpatial services to the user community. Established in 2002, SATPALDA has successfully completed wide range of photogrammetric and Remote Sensing Projects.

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