New Methods Of Ranging Between Two Points

Ranging
It is a process of establishing intermediate point on a start line between the terminal points or station.

Methods of Ranging

There are two method of ranging

• Direct ranging
• In-direct ranging

Direct Ranging:

This kind of ranging is in process when all points are visible. As shown in the figure.

In-Direct 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. 

Let A and B be the two station with rising ground or a hill between them (Fig. Indirect Ranging, Case-I)

Let two chainmen with ranging rod take up point at M1 and P1 (Fig. Intermediate Points- M,P) as nearly in line as they can judge and such that chainmen at M1 can see both the ranging rods at measurement of distance P1 and B and the chainmen at P1 can see the ranging rod at M1 and A.

The two chainmen than proceed to line in each other alternately, the chainmen at P1 directs the chainmen at M1 to M2 in line with A, and then the chainmen at M2 directs the chainmen at P1 to P2 in line with B. By successively direction each other into line, their position will be change until finally they are both in the line AB exactly, (i.e. the four ranging rods A, M, P and B are in the same straight line) when they fix their ranging rod.

The Position of these ranging rods (M and P) serves as intermediate stations for ranging the line and enables the chainmen to measure in a straight line between A and B. this method may also be used in ranging a line across a hollow as illustrated in (fig. Indirect Ranging, Case-II)

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Compass Surveying | Advantages and Disadvantages?

Compass surveying has some advantages and disadvantages that one need to know  before choosing the surveying type. Some of them are discussed below.

Advantages of Compass Survey

In compass surveying, the compass needs much less time in setting as it is very light and portable. The mechanism of the instrument is very easy. It is very simple to take bearing with the instrument. An error in the direction of one does not necessarily affect the other lines. To retrace old surveys it is very suitable.

Disadvantages of Compass Survey

The disadvantages of compass surveying includes that it is less precise and very often subject to errors due to the fact that the needle is not perfectly straight or needle is not sensitive. Sometimes the plane of sight is not vertical or the vertical hair being too thick or loose. Errors may also arise due to inaccurate leveling of the compass, imperfect sighting of the ranging rods and mistakes in recording bearings and lengths. There may be errors in compass surveying due to local attraction, variation of magnetic meridian and magnetic changes in the atmosphere.

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Basic Definition of Surveying in Civil engineering

The simplest definition of surveying is that : 

The definition of surveying include these main points

1) earth measurement

• distances : horizontal ,slope and vertical

• angles :horizontal , vertical , zenith , azimuth     

2) determination of relative position of points located on above or below the earth's surface

3) The final output is positional information as :

• maps : digital or paper 
• Coordinates 
• Features  
  
  

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Surveying types and their needs in Civil engineering

1) boundary and cadastral surveying 

• Related to separation and mapping of property boundaries .

2) plane surveying 

• concerns small area project and surveying work where earth curvature can be neglected .

3) Topographic surveying 

• The third dimension - heights - is included .

4 ) Geodetic surveying 

• concerns large area surveying works such as geodetic networks , etc . 
• earth curvature is taken into account .

5) Engineering construction surveying includes surveying works needed for 

• planning 
• design
• Implementation 
• Monitoring 

6 ) Quantity surveying 

field works and computations related to determination of quantities :

• cut 
• fill
• buildings materials , etc 
  
  

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Land surveying and their Needs in Civil Engineering

This area of surveying can be broken down into the following:

• Geodetic surveying .
• Topographical surveying  .
• Photogrammetry.
• Hydrographic surveying.
• Cadastral surveying .
• Engineering surveying .

We are going to concentrate on this last aspect although the basic techniques can be employed to most of the others .

Engineering surveying is used 

•  at the concept and design stage for production of maps and plans .
• at the construction stage for setting out and measurement .
• at the post construction stage for measurement and monitoring .

surveying for all three aspects involves the measurement of three parameters :

• Horizontal distances .
• Vertical distances .
• Angles .

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Methods and Equipments used in measuring

a variety of methods and equipments can be used to measure each of these parameters .

1)Horizontal distances by :

• Taping .
• Optical method .
• Electronic methods  .

2)Vertical distances by : 

• Taping 
• Optical method 
• Electronic methods  

3)Angles by :

• Magnetic compass .
• Sextant .
• Theodolite .

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Conversions of unit of measuring in Surveying

As a student you must store these basic parameters in your mind to use it but in future you can used a lot of alternatives to convert between units 

• 1 yard = 3 feet 
• 1 meter = 39.37 inch = 3.2808 feet
• 1 degree = 1/ 360 of the angle around a point  
• 1 degree = 60 minutes 
• 1 radian = 57.3 degrees 
• 1meter = 100 cm = 1000 mm = 1.0936 yd 
• 1 kilometer = 1000 m = 0.6214 mile 
• 1 foot = 12 inch 
• 1 mile = 1760 yd 
• 1 hectare = 10000m square 
• 1 square kilometer = 100 hectare 

This the most important point you can use in conversions . 

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Sources Of Errors in Surveying

 

1) personal errors 

no surveyor has perfect senses of sight and touch 

2) Instrument errors 

devices cannot be manufactured perfectly wear and tear and 

compatibility with other components  .

3 ) Natural error 

temperature , wind , moisture , magnetic variation , etc .

4) Systematic error 

Known as cumulative errors .

Correction can be made to eliminate them .  

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Equipments used with taping in Surveying

1) Plumb bob 

• Used to ensure a horizontal reading is obtained .

2) Range poles 

• painted alternately red and white .
• Used as upright guides when chaining or marking turning points .

Types of tapes : great variety exists :

1) According to the material : 

• steel and steel alloy 
• metallic or non-metallic 
• polymers 
• Invar 

       1) nickle - steel alloy .

       2) with very low coefficient of thermal expansion .

       3) Used for precise measurements .

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Types of tapes in Surveying

 

According to graduation

• •In metric or imperial units

• •Different location of zero mark

• •Least graduation interval

                Millimeters, centimeters, or decimeters           
         

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