Chain Surveying: Types, Principles & Obstacles in Chain Surveying
Chain surveying is the branch of surveying in which only linear measurements are made in the field. This is suitable for the survey of small areas with simple details and a fairly flat area. It works on the principle of Chain Triangulation. This means that the area to survey is spilled into several small triangles.
Chain Surveying is a classical method of surveying which is often used by many of the Government Bodies such as the State and Central Revenue Department as it is easy to use and requires hardly any knowledge to interpret. But sometimes it leads to linear error as the chain is not so flexible. This method of survey is adopted where the land surface is flat or not so uneven, and the survey area is comparatively small.
The things followed during chain surveying are as below-
The area is divided into triangles as they are the simplest closed figure and relative points are measured. This is the basic principle of Chain Surveying. The linear length is measured using the taps of chain and the angle is measured using compass. As triangulation forms the basic of Chain Surveying, it sometimes is referred as Chain Triangulation.
The primary triangle (or basic triangle or 1st triangle) is surveyed very precisely so that errors are not transformed to the secondary triangles.
For minimum transfer of error, triangles are supposed to be well-proportioned i.e. angle should be between 30 degrees to 120 degrees.
Elements of Chain Surveying
Let us now discuss, what are the elements we require to carry out the chain surveying. Chains and arrows are the basic elements. Chain is nothing but a linear arrangement of multiple links. The links are made up of mild steel. The arrows are the marking points which help the surveyor to keep a record of the distance or mark a/an intermediate point.
Ranging rods are 2 m – 3 m high rods of steel or well-seasoned wood utilized the ranging of point. They are coated in alternate colors of the band either white and black, white and red, or black, white, and red in series.
A plumb bob is also required to transfer a point while measuring the horizontal distance where the surface is uneven. It helps to minimize the human error.
Except all these major items, we also need pegs, measuring tape, and hammer for obvious reasons.
Types of Chain
Several types of Chains can be used for surveying-
Metric Chain - This is the mostly used chain in India. The length of most commonly used metric chain is 20 meter. Other than 20 meter chain, 5 m, 10 m, 30 m chains are also available.
Gunter’s Chain - 66 ft. in length and contains 100 links.
Engineers’ Chain - 100 ft. in length and contains 100 links. The 10 links segments are clamped with notches for easy reference purpose.
Revenue Chain - 33 ft. in length and has10 links.
How to do Chain Surveying?
The important steps we follow while chain surveying are-
Reconnaissance: It is the preliminary phase of each type of surveying. This step includes inspection of the land and preparing the key plan according to the inspection.
Station Fixing: The station should be fixed in a such way that, most of the points can be surveyed and we get a maximum area accessible from the same point. This step included fixing of ranging rods and driving pegs.
After the station is fixed, the chaining can be initiated and ranging is done wherever needed.
Measure the links and enter the observation in the filed book, for further circulation.
The advantages of chain surveying are
It is the easiest and can be understood by everyone, so the commonest method adopted.
The elements of a chain can easily be replaced and easy to transport from one to other place.
It does not involve any complex calculation and mathematics.
The manpower required to carryout the survey is limited.
It cannot be used for surfaces having many undulations and having steep slopes or waterlogged areas.
For large areas, this can not be adopted, as it will be very time consuming.
If the area is crowded with many details, it becomes complicated to markup the points and ranging.
A simple chain survey is subject to various changes of errors of accumulation which may cause by the difficulty of the chain.
Obstacles in Chain Surveying
There can be many obstacles while surveying and for each obstacle there are solutions. Now let us see those obstacles one by one.
Obstacle to ranging
Obstacles to ranging can be due to hills, trees, or intervening ground. There is no obstacle to chaining. These obstacles can be overcome by reciprocal ranging.
Obstacle to chaining but not to ranging
In this type the ends of lines are visible but chaining is obstructed by ponds, lakes. This can be sorted by shifting points parallel to a position where there is no obstacle to chaining.
Obstacle to both chaining and ranging
Here there is an obstruction to both chaining and ranging. An example of this type of obstacle is building. Geometry can be used to overcome this.
For more information and better understanding please do watch the below video
Thank you for going through the blog. Solve this question to understand Chain Surveying better.