Q1: What is the principle of plane tabling?
Ans:The principle of plane tabling is parallelism, meaning that the rays drawn from stations to objects on the paper are parallel to the lines from the stations to the objects on the ground. The relative positions of objects on the ground are represented by their plotted positions on the paper and lie on the respective rays.
Q2: What is orientation? Why is it done?
Ans:Orientation is the method of setting up the plane table at each successive station parallel to the position it occupied at the starting station. It ensures the accuracy of the map by keeping the relative positions of objects correct.
Q3: How are centring and levelling done in plane tabling?
Ans:Centring is done by adjusting the plane table so that a selected point on the drawing sheet is exactly above the ground station. Levelling is done using a spirit level to ensure the table is horizontal.
Q4: What are the methods of plane tabling?
Ans:The four methods of plane tabling are:
• Radiation
• Intersection
• Traversing
• Resection
Q5: When would you apply resection?
Ans:Resection is applied when it is necessary to establish new survey stations at a place to locate missing details.
Q6: What is intersection? When is it required?
Ans:Intersection is a method used to locate inaccessible points by drawing rays from two instrument stations. It is required when objects cannot be directly measured from a single station.
Q7: When would you apply the two-point and three-point problem?
Ans:The two-point and three-point problems are applied in orientation and resection when locating points with reference to known stations.
Q8: What do the terms 'great triangle' and 'great circle’ mean?
Ans:A great triangle is formed by three known points in surveying, and a great circle is the largest possible circle that can be drawn on a sphere, such as the Earth's surface.
Q9: One month after the completion of a plane table survey, it is detected that one important object was not plotted. How will you plot the object on going to the field?
Ans:The object can be plotted by relocating the original plane table stations using reference sketches and reorienting the table accordingly.
Q10: What type of orientation would you prefer and why?
Ans:Orientation by back-sighting is preferred as it is more accurate than using a magnetic needle.
Q11: What method would you apply for locating inaccessible points?
Ans:The intersection method is used for locating inaccessible points by taking sightings from two different stations.
Q12: What do you mean by the ‘fiducial edge’ of the alidade?
Ans:The fiducial edge of the alidade is the working edge along which rays are drawn on the plane table sheet.
Q13: What are the different types of alidade?
Ans:The two types of alidade are:
• Plain alidade
• Telescopic alidade
Q14: What do you mean by 'strength of fix’?
Ans:The strength of fix refers to the accuracy with which a station can be determined in plane tabling.
Q15: What are the precautions you have to take while centering the alidade with the station pin?
Ans:Precautions include ensuring proper levelling, securing the table against movement, and checking for local attraction before aligning the alidade.