Chain Surveying – Prolonging a Chain Line Across an Obstruction When a chain line is obstructed by a pond, building, or other obstacle, which of the following techniques may be used in practice to prolong the line across the obstruction?

Introduction / Context:
Obstructions commonly interrupt straight chain lines. Competent surveyors must know several field methods to regain the alignment beyond the obstacle while maintaining accuracy. This question assesses recognition of acceptable techniques used in routine practice.

Given Data / Assumptions:

• There is no direct path for chaining.
• Nearby ground permits auxiliary setups or offsets.
• A straight line must be continued past the obstruction.

Concept / Approach:

Options include: (1) Angular measurement around the obstacle using a theodolite/compass with short traverse legs, then resecting the continuation; (2) Offset methods using perpendiculars/parallel lines established by chain or tape to port the line; (3) Triangulation by establishing auxiliary points and solving triangles to compute the continuation. Each method is standard and chosen based on site constraints and required accuracy.

Step-by-Step Solution:

Verification / Alternative check:

Field manuals include detailed sketches for each technique, confirming they are all accepted solutions for prolonging a chain line.

Why Other Options Are Wrong:

“None of the above” is incorrect because each listed method is a legitimate approach used by surveyors.

Common Pitfalls:

Failing to close and check a small traverse around the obstacle; poor right-angle formation when using chain-only methods; neglecting to tie in control points for verification.

Final Answer:

All of the above