About Lesson
Obstacles in Chain Survey
a. Ranging Possible, Chaining Obstructed (e.g., pond)
- Rectangle method: Erect equal perpendiculars and connect.
- Right-angled triangle: Use perpendicular and apply Pythagoras theorem.
- Triangle enclosing obstacle: Use cosine rule.
- Similar triangles: Set equal distances and measure connecting line.
b. Chaining Possible, Ranging Obstructed (e.g., hill)
- Reciprocal Ranging: Use intermediate points to align line.
- Random Line Method: Divert and use similar triangles to correct.
c. Both Chaining & Ranging Obstructed (e.g., building)
- Use symmetry, perpendiculars, and similar triangles to transfer line beyond obstacle.
- Often involves constructing equilateral triangles, arcs, or mirrored triangles.