Levelling, Contours, Areas & Volumes Quiz

Levelling and Contours

• A Level Line is parallel to the mean spheroidal surface of the Earth, providing a reference for elevation measurements.
• Reducing Levels (R.L) calculations involve back sight and foresight readings to determine the R.L. of different stations, illustrating the application of fore- and backgrounds in surveying.
• The rise and fall method is utilized to check the accuracy of intermediate point level reductions.

Temperature and Sensitivity

• The sensitivity of a bubble tube decreases with rising temperatures, impacting the precision of leveling instruments.
• Increasing the diameter of a bubble tube enhances its sensitivity, affecting measurement accuracy.

Contouring Techniques

• Contour gradients represent imaginary lines on the ground maintaining a constant slope, crucial for understanding terrain changes.
• A suitable contour interval for a map scaled at 1:10,000 is typically 2 meters, aiding visual representation of elevation changes.
• A series of closely spaced contour lines indicates steep slopes, which are essential for terrain evaluation.

Methods of Contouring

• The direct method of contouring is recognized as the most accurate technique for determining elevation points.
• Vertical control in direct contouring identifies points along a contour accurately, ensuring precision in mapping.
• Errors from curvature and refraction can be neutralized by positioning the level instrument midway between two points.

Elevation Measurements

• The R.L. of point B on a ceiling can be determined using foresight and back sight measurements, demonstrating practical applications of leveling.
• Datum describes an imaginary level surface from which all elevation measurements are referenced, critical for establishing uniformity in surveys.

Benchmarking

• GTS Benchmarks are established by the Survey of India, designed with high precision to serve as reference points across the country for surveying tasks.

Line of Sight and Instrument Adjustment

• Height of Collimation refers to the line of sight between the optical center of the object glass and cross bars, affecting measurement accuracy.
• Temporary adjustments needed for leveling instruments include setting up the level, leveling the telescope, and focusing the eye-piece and object glass to ensure clear readings.

Advanced Techniques and Area Calculations

• Inverted Levelling is used to find heights of points above a line of sight, useful in construction and bridge assessments.
• The horizontal distance between adjacent contours is referred to as Contour Equivalent or Horizontal Equivalent, pivotal for understanding terrain layout.
• Simpson's Method provides a higher accuracy for area calculations involving irregular boundaries modeled as parabolic arcs, requiring an odd number of ordinates for effective application.

Closed Contours

• Closed contours with higher values towards the center indicate hillocks, while decreasing values signify depressions or ponds, essential for interpreting natural landforms accurately.