Orientation in Plane Table Surveying refers to the process of aligning the plane table and alidade with the north-south direction. This is important because it ensures that the readings taken and the sketches made on the plane table are correctly aligned with the earth's magnetic field, which helps to prevent errors in the survey results.
There are several methods used to determine orientation in Plane Table Surveying, including:
Magnetic compass: A magnetic compass can be used to determine the north-south direction. The surveyor aligns the plane table and alidade with the direction indicated by the compass, and then takes readings and makes sketches on the plane table.
Solar method: In the solar method, the surveyor uses the sun to determine the north-south direction. This is done by observing the position of the sun at midday, when it is directly overhead. The plane table and alidade are then aligned with the shadow cast by a vertical object, such as a rod or pole.
Back-sight method: In the back-sight method, the surveyor takes readings of a known point or monument, such as a building or a road. The plane table and alidade are then aligned with these readings, which helps to ensure correct orientation.
Once the plane table and alidade are correctly oriented, the surveyor can take readings and make sketches on the plane table, confident that they are accurately aligned with the north-south direction. This helps to ensure that the survey results are accurate and reliable.
In summary, orientation in Plane Table Surveying refers to the process of aligning the plane table and alidade with the north-south direction. There are several methods used to determine orientation, including the magnetic compass, solar method, and back-sight method, and each method helps to ensure that the survey results are accurate and reliable.
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