Plane Table Surveying Errors Explained
Plane table surveying is a graphical field method where the survey work and plotting occur simultaneously. This method is simple but prone to various errors. Understanding these errors is crucial for accurate results.
Analysis of Potential Errors
Let's examine the common errors that can occur:
- Error in Sighting: This involves inaccuracies when aligning the alidade's edge with the object point. While possible, careful observation minimizes this.
- Error in Leveling: Ensuring the plane table is perfectly level is important. However, minor deviations might not significantly skew the results on the map unless the instrument is severely tilted.
- Error in Measurement: Errors can occur when measuring distances on the ground or transferring them to the drawing using the scale. These are standard measurement inaccuracies.
- Error in Orientation: This is a critical error specific to plane table surveying. Orientation involves aligning the drawing board so that lines drawn from different stations correspond to the actual directions on the ground. If the table is not correctly oriented (e.g., parallel to the corresponding lines on the plan) after moving to a new station, all subsequent sightings and plot points will be wrongly positioned relative to the previous work.
Most Likely Error Identification
Orientation errors are considered the most likely and potentially damaging in plane table surveying. This is because:
- The process involves repeatedly moving the instrument and re-orienting it relative to the previous station or a known direction.
- Failure to maintain accurate orientation between stations leads to cumulative errors in the plotted positions and directions.
- Unlike sighting or leveling, which are often checked during the setup of each point, orientation requires careful comparison with the plan or a reference direction, making it prone to oversight in field conditions.
Therefore, errors in orientation significantly compromise the geometric accuracy of the map being produced.
