Compass survey

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 is a branch of that deal with the fixing of an objects position in the field by measuring the angles of bearings between the time of magnetic north and the line of sight to the object .It is a branch of surveying in which directions surveying lines are determined with a compass and the length of lines are measured with a tape or chain. Tape or chain is used for linear measurement and compass is used  for fixing direction .The freely suspended magnetic needles directs to north- south and the bearing of line obtained by line of sight equipment used is magnetic  compass, ranging poles , leveling, field sheet,
         Magnetic compass survey
   Refers to the type of survey which deal with direction measurement during surveying
          ERRORS IN COMPASS SURVEY
1.      Instrumental errors, they are those which arise due to the fault adjustment in instrument
·        The needle not being perfectly straight ,
·        Slugglish  needle
·        Pivot bent
·        Improper balancing weight
·        Blunt pivot point
2.       Personal errors , Those are errors which caused by a surveyors during survey which are inaccurate leveling ,inaccurate centering and inaccurate bisection
3.      Natural errors, This are types of errors which occurs naturally during survey those are like local attraction due to errors around , irregular variation due to storms

                       Ways to overcome errors in magnetic compass survey
1.      The deviation errors caused by magnetism in the ships structure are minimized by precisely positioning small magnets and iron compensate for the induced magnetization two magnetically soft iron spheres are placed on side arms
2.      Check the accuracy of the compass by comparing with an accurate compass or with location of magnetic North for the years of survey
3.      To avoid local attraction , when conducting magnetic compass survey avoid those material which made by iron errors , watch and rings which made by iron can hinder conducting the survey on a particular place
4.      When using a compass avoid wearing metal material like rings , spectacles ,bangles and watches which can act as the magnet to the compass magnetic instrument
5.      Be careful to the booker by asking him or her to repeat reading all figures verbally because there are some mistakes in writing and reading of point during the survey
6.      Hold the compass steadying when bearing are  taking place
7.      Before the transit is moved or taken up, you should center the instrument on the foot plate roughly equalize the height of the leveling screw, sclamp, the upper motion (the lower motion may be tightened lightly)and point telescope vertically up ward and also lightly in vertical motion clamp
                                    


REFERENCE
     Kulkarni &kanetkar (2011).Surveying and leveling .
    


      Generally magnetic compass survey have various advantages like it help to know the direction during navigation activities ,it covers a large area , its instruments are more portable also it is not time consuming .


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