Prismatic compass surveying is the method of surveying in which the direction of surveying lines and angular measurements are determined with a magnetic compass and the length of surveying lines are measured with a tape or chain.
The following are principles of prismatic compass surveying
Principle 1: Avoid Magnetic Materials for Accurate Readings
In prismatic compass surveying, an essential principle is to ensure that no magnetic materials are present in the vicinity of the compass during measurements. This precaution is paramount as magnetic materials can interfere with the accuracy of the compass readings. Magnetic materials, such as iron or steel, have the capability to influence the direction of the compass needle due to their inherent magnetic properties. This can lead to erroneous readings and significantly compromise the reliability of the survey data collected.
By adhering to this principle, surveyors can safeguard the integrity of their measurements and prevent the introduction of systematic errors. This involves meticulously checking the surveying area for any potential sources of magnetic interference, such as tools, equipment, or structures that might contain magnetic elements. This proactive step of eliminating magnetic materials from the surroundings of the compass ensures that the readings obtained are a true reflection of the earth’s magnetic field, enhancing the overall accuracy of the survey results.
Principle 2: Steady Compass Handling to Minimize Errors
A fundamental principle in prismatic compass surveying is the steady and consistent handling of the compass during measurements. Holding the prismatic compass steady is vital to prevent the accumulation of errors that may arise from even the slightest movements. The compass needle is highly sensitive to movements and external vibrations, which can cause oscillations and result in inaccurate readings.
To adhere to this principle, surveyors must maintain a stable posture while taking compass readings. This involves holding the compass steadily at the proper height and ensuring that the compass is level and oriented correctly. Avoiding sudden movements, jostling, or brisk rotations can significantly reduce the introduction of errors. By adopting a deliberate and controlled approach to compass handling, surveyors can minimize the impact of instrumental errors and enhance the reliability of the collected data.
Principle 3: Avoid Wrist Watches to Prevent Interference
In prismatic compass surveying, a lesser-known yet crucial principle is to avoid wearing wrist watches while conducting measurements. Wrist watches, especially those with magnetic components, can exert a magnetic influence on the compass needle, leading to erroneous readings. The presence of a wrist watch in close proximity to the compass can disrupt the natural alignment of the needle with the earth’s magnetic field, introducing inaccuracies into the measurements.
By adhering to this principle, surveyors can maintain the accuracy of their compass readings by eliminating potential sources of magnetic interference. This involves either removing wrist watches before using the compass or ensuring that they are positioned at a sufficient distance to prevent any unintended magnetic interaction.
Principle 4: Verify Instrument Accuracy Before Use
Before embarking on any surveying activity, it is essential to verify the accuracy of the instruments being used, including the prismatic compass, chain, and tape. This principle underlines the importance of instrument calibration and checks to ensure that measurements are reliable and consistent.
Surveyors should routinely calibrate their instruments and assess their accuracy using established benchmark points or reference measurements. This calibration process involves confirming that the compass readings align with known reference directions and that the chain and tape provide accurate measurements over a known distance. Regular instrument checks help identify and rectify any discrepancies, ensuring that the survey data collected is dependable and aligned with the desired level of accuracy.
By adhering to these principles, prismatic compass surveyors can uphold the integrity of their measurements, minimize errors, and produce reliable survey data that serves as a foundation for informed decision-making in various applications.