Plane table plotting of inaccessible points On a plane table, which method is used to plot the position of an inaccessible point when you can occupy two (or more) accessible stations with known plan positions?

Introduction / Context:
Plane table surveying allows direct plotting in the field. When a point cannot be occupied or measured directly (due to obstacles or hazards), we choose a method that does not require taping to the point but still fixes it accurately on the plan. This question asks you to identify that method.

Given Data / Assumptions:

• Two or more accessible instrument stations with known plan positions are available.
• The target point cannot be physically reached for measurement.
• Sighting to the point is possible.

Concept / Approach:

The intersection method fixes the point by drawing rays from at least two occupied stations whose plan positions are already plotted. The intersection of these rays on the drawing sheet gives the location of the inaccessible point. This avoids chaining or occupying the point itself, unlike radiation or traversing that typically require measuring distances or moving the table successively.

Step-by-Step Solution:

Verification / Alternative check:

Using more than two rays from additional stations allows a check for plotting accuracy (the rays should concur at a single point).

Why Other Options Are Wrong:

Radiation requires measuring distance from a single occupied point. Traversing is for establishing control by moving the table between stations. “None” and “tacheometry only” do not reflect standard plane-table methods.

Common Pitfalls:

Poor station geometry (very small intersection angle) leading to large positional uncertainty; ensure good intersection angles.

Final Answer:

Intersection