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Which of the following statements are correct In chain/tape surveying, the 3-4-5 method can be used: i. to setout contour line ii. to draw a perpendicular line to the chain line, iii. to draw a perpendicular offset, iv. to remove the obstacle to ranging.
iii and iv
i and iv
ii and iii
ii and iv
ii and iii
The 3-4-5 method is a practical application of the Pythagorean theorem used in field surveying to construct a right angle. By forming a triangle with sides in the ratio 3:4:5, a 90┬░ angle is accurately set out for drawing perpendiculars or offsets from a survey line.
The 3-4-5 method is a practical application of the Pythagorean theorem used in field surveying to construct a right angle. By forming a triangle with sides in the ratio 3:4:5, a 90┬░ angle is accurately set out for drawing perpendiculars or offsets from a survey line.
a2+b2=c2 тАФ The Pythagorean theorem where a=3,b=4,c=5
sin(90┬░)=1 тАФ The trigonometric basis for perpendicularity
The principle relies on the converse of the Pythagorean theorem, where for a triangle with side lengths a,b,c, if a2+b2=c2, the angle opposite side c is exactly 90┬░. In the field, surveyors use a tape to measure lengths of 3x,4x,┬аand┬а5x units to establish this geometric perpendicularity.
It is a field method for setting out right angles without using optical instruments.
Used extensively for establishing perpendicular offsets from a base chain line.
The accuracy of the method depends on the precision of the tape measurements.
It cannot be used for ranging or contouring as these require line extension and elevation profiling respectively.
Does not require expensive optical instruments like a cross staff or prism square.
Easy to implement with just a standard measuring tape.
Time-consuming for long offsets compared to optical squares.
Subject to human error in tape handling and tension.
Drawing perpendicular offsets to chain lines.
Setting out building foundation corners.
Laying out grid patterns on site.
i (Contour line) and iv (Obstacle to ranging) are incorrect. Contouring requires levelling instruments (Dumpy level/Total station), and obstacles to ranging involve specific methods like setting up triangles or parallel lines to bypass an obstacle, not a 3-4-5 triangle.
The 3-4-5 method is specifically categorized under 'Methods of setting out right angles'.
C is correct тАФ The 3-4-5 method is specifically used for drawing a perpendicular line and setting out perpendicular offsets from a chain line.
Always remember that the 3-4-5 method is for 'geometry of angles' and cannot be used for 'levelling' (contouring) or 'ranging' (alignment of points).
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