Local attraction in compass surveying may exist due to, options are. Instruments for measuring distance and ranging, units of measurement in surveying. Unless the local attraction at a place is found out and corrected, the bearings taken from. Magnetic north may deviate from true north due to local attraction or magnetic declination. We know that even if the local attraction is present at every. If local attraction exists at any traverse station, both the forward and back bearings are affected equally. It was found that the station was affected by local attraction. Local attraction when a magnetic needle is disturbed from its normal position due to influence of external forces such as electric current or magnetic substances, local attraction is said to have occurred. It is the art of measuring horizontal and vertical distances between objects, of measuring angles between lines, of determining the direction of lines, and of establishing points by predetermined angular and linear measurements. Local attraction affects all bearings observed at a point by equal amount and in the same direction. The horizontal angle between the true meridian and magnetic meridian at a place is called a azimuth b declination c local attraction. Surveying i traverse survey aau, department of civil engineering, 2009 2 observed for all lines and astronomic observations are made periodically. Compass surveying is not recommended for areas where local attraction is suspected due to the presence of magnetic substances like steel structures, iron ore deposits, electric cables conveying current, and so on.
According to the method employed, surveying is classified into triangulation. Local attraction affects all bearings observed at a point. While compass surveying, the magnetic needle is sometimes disturbed from its normal position under the influence of external attractive forces. Local attraction compass surveying hello, local attraction. Civil engineering surveying questions and answers pdf. Engineering surveying lecture notesebook pdf download. The bearing of the line in the direction of progress of a survey is called fore bearing fb, while the bearing in. The term is also used to denote amount of deviation of. While compass surveying, the magnetic needle is sometimes disturbed from its normal position. Combining newtons second law with his law of mutual attraction, the gravitational acceleration on the mass m2 can be shown to be equal to the mass of attracting object, m1. Methods for correcting the bearings affected by local. This volume is one of the two which offer a comprehensive course in those parts of theory and practice of plane and geodetic surveying that are most commonly used by civil engineers. Surveying pdf interview questions pdf surveying multiple choice questions and answers.
The most up to date version was published in june of 2007. True meridian magnetic meridian dip compass surveying. If local attraction is detected in a compass survey observed bearings may be corrected by any one of the following two methods. A compass shows the direction of the magnetic meridian on the principle of magnetism. Local attraction is the phenomenon by which the magnetic needle is constantly prevented to point towards the magnetic north at a place. As already stated in the last section, surveying which involves a series of connected lines is known as. Local attraction in compass surveying may exist due to. This article provides a note on local attraction along with its remedies and examples. If the difference is exactly 180, the two stations may be considered as not affected by local attraction. Professionals, teachers, students and kids trivia quizzes to. The mndot surveying and mapping manual is periodically revised and supplemented. Prismatic compass, true and magnetic bearing, local attraction, compass traversing. The external forces are produced by sources of local attraction which may be current carrying wire magnetic materials or metal objects.
The first volume covers in 24 chapters, the most common surveying operations. Aline or plane passing through geographical north pole and geographical south pole magnetic meridian. Line or plane passing through geographical north pole and geographical south pole magnetic meridian. Charles ghilani is a professor of engineering in the b. Such a disturbing influence is known as local attraction. Dip inclination of the needle with the horizontal is called dip of the needle. How is it detected with the data of compass survey. Local attraction in compass surveying elimination methods. Aait, department of civil engineering 3 lecture note. This is because that these magnetic compass is influenced by other magnetic objects at that locality such as wires carrying electric current, rails, steel and iron structures, steel tapes etc. Such a disturbing influence is called as local attraction. If local attraction exists at any traverse station, both the.
Below are the bearings observed in a traverse survey problems on. Geophysical surveying using gravity introduction gravity. This inclination of the needle with the horizontal is known as dip of the magnetic needle. Any magnet attracting material, when is brought near to the compass needle, needle will deflect from the true magnetic north. In the quadrantal bearing system, a whole circle bearing of 293 30.
April 2004 figure 1 the three main types of levels. Surveying and levelling multiple choice questions and. These sample surveying objective type questions are framed by experts. Local attraction method of correction for traverse. When the magnetic needle is suspended freely and balanced properly, unaffected by magnetic substances, it indicates a direction. Compass surveying principles use of prismatic compass, measurement of bearings, conversion of bearings, local attraction, correction of compass traverse.
Surveying multiple choice questions with answers pdf. The imaginary level surface with reference to which vertical distance of the points above or below are measured, is called datum surface. The existence of local attraction can be detected by recording the fore bearing and back bearing of the survey line from both end stations. Local attraction in compass surveying may exist due to a incorrect levelling of the magnetic needle b loss of magnetism of. Local attraction method of correction for traverse first.
Local attraction in compass surveying may exist due to a incorrect levelling of the magnetic needle b loss of magnetism of the needle c friction of the needle at the pivot d presence of magnetic substances near the instrument ans. A incorrect levelling of the magnetic needle, b loss of magnetism of the needle, c friction of the needle at the pivot, d presence of magnetic substances near the instrument, e. Prismatic compass surveying pdf notes expert civil. The branch of surveying in which direction of survey line are determine by a compass and their length by a chain or tape is called compass surveying. Surveyor is expected to take care to avoid local attractions listed in iii and iv above. Syllabus for mine surveying part test 1 online mining exam. Geoinformatics definition, disciplines covered, importance. The magnetic needle is disturbed from its normal position if it is under the influence of external attractive forces called the sources of local attraction. Watch easy method to find the value of corrected angle free from local attraction as well as bearing also. Civil engineering surveying important mcq pdf all exam. June 2012 introduction most people have an understanding that surveying is only restricted to field work on construction sites. In such a situation magnetic needle does not point towards north south. Local attraction, correcting the bearings for local attraction. Nptel syllabus surveying video course basic surveying or geoinformatics 1.
1121 703 880 1484 748 1248 1413 871 205 386 74 622 795 1204 1351 140 374 1346 991 102 1360 222 210 657 1208 44 738 187 108 97 690 621 1414 1210 636 1141 135 648 1126 464 1490 779 237 567 129