RECONNAISSANCE SURVEY AND INDEX SKETCH

Before the commencement of any survey work, the area to be surveyed is thoroughly examined by the surveyor, who then thinks about the possible arrangement of the framework of survey. This primary investigation of the area is termed as reconnaissance survey or reconnoitre.

    During reconnaissance survey, the surveyor should walk over the area and note the various obstacles and whether or not the selected stations are intervisiable. The main stations should be so selected that they enclose the whole area,. The surveyor should also take care that the triangles formed are well conditioned. He  should note the various objects which are to be located.

    The neat hand sketch of the area which is prepared during reconnaissance survey is known as the index sketch or key plan. The index sketch shows the skeleton of the survey work. It indicates the main survey stations, sub-station, tie stations, base line, arrangement for framework of triangles documents for the surveyor and for the person who will plot the map. It should be attached to the starting page of the filed book(Fig. 2.2) 

                       

WE'LL-CONDITIONED AND I'LL-CONDITIONED TRIANGLES

A triangle is said to be well conditioned when no angle in it is less than 30' or greater than 120'.An equilateral triangle is considered to be the best-condition or ideal triangle[Figs 2.1 (a) and (b) ].

        We'll-conditioned triangles are preferred because their apex points are very sharp and can be located by a single 'dot'. In such a case, there is no possibility of relative displacement of the plotted point.

        A triangle in which an angle is less than 30' or more than 120' is said to be i'll conditioned[Fig. 2.1(C)].

                 

         

I'll-condoned triangles are not used in chain surveying. This is because their apex points are not sharp and well defined, which is why a slight displacement of these points may cause considerable error in plotting.

CHAIN SURVEYING

• PRINCIPLE OF CHAIN SURVEYING     

The principle of chain surveying is triangulation. This means that the area to be surveyed is divided into a number of small triangles which should be well conditioned. In chain surveying, the no angular measurements are taken. Here, the tie lines and check lines control the accuracy of work.

      It should be noted that plotting triangles requires no angular measurements to be made, if the three sides are known  

          Chain surveying is recommended when

               1.The ground surface is more or less level

               2.A small area is to br surveyed,   

               3.A small-scale map is to be prepared, and

               4.The formation of we'll-conditioned triangles is easy. 

          Chain surveying is unsuitable when

               1.The are is crowded with many details, 

               2.The area consists of too many undulations, 

               3.The area is very large, and

               4.The formation of well-conditioned triangles becomes difficult due to obstacles. 

Large-Scale and Small-Scale Maps

When 1 cm of a map represent a small distance, it is said to be a large-scale map. 

      For example, 

                                    1 cm =1 m, I. e.   RF = 1/100

When 1 cm of the map represents a large distance, it is called a small-scale map. 

          For example, 

                                      1 cm = 100 m,  I. e.   1 RF = 1/10000

    A map having an RF of less than 1/500 is considered to be large-scale. A map of RF more than 1/500 is said to be small-scale.


                 

     

        

Chain survey

Multiple-choice question:-

 1.The working principle of the optical square is based on

          A. Reflection

          B. Refraction

          C. Double reflection

     Ans:Double reflection  

 2.The field records of the chain survey is entered in a/an

          A. Exercise book

          B. Field book

          C. Level book

     Ans:Field book 

 3.The chainman who drags the chain is called the

          A. Captain

          B. Leader

          C. Follower

     Ans:Leader

 1
 4.The preliminary inspection of the area to be surveyed is known as

          A. Primary survey

          B. Reconnaissance survey

          C. Rout survey

     Ans:Reconnaissance survey 

 5.The limiting length of offset depends upon the

          A. Scale of plotting

          B. Method of measurement

          C. Method of layout 

     Ans:Scale of plotting 

 6.The main survey stations are located on the ground by

          A. Index sketches

          B. Reference sketches

          C. Line sketch

     Ans:Reference sketches
             
           
               

Chain survey some multiple choice questions

1.Chain survey is recommended when the area is

        A. Crowded

     

        B. Undulating

        C. Simple and fairly level

    Ans:Simple and fairly level

2.In chain survey, the area is divided into

         A. Rectangles

         B. Triangles

         C. Squares

     Ans:Triangles

3.The sketch prepared during reconnaissance  survey is known as the 

         A. Hand sketch

         B. Index sketch

         C. Rough sketch

    Ans:Index sketch

4.A triangle is said to be well-conditioned when it's angle should lie between

         A. 30' and 120'

         B. 20' and 150'

         C. 15' and 135'

    Ans:30' and 120'