Ranging

• Ranging is the process of establishing intermediate points on a straight line between two end points before chaining begins.
• Ensures accurate alignment of the survey line.

Methods of Ranging

A. Direct Ranging

• Used when end stations are intervisible (can be seen from one another).
• Carried out by naked eye or using line ranger.

Procedure:

• Two ranging rods placed at end points A and B.
• Surveyor stands behind A, assistant holds rod at intermediate point P.
• Assistant moves rod left or right as directed.
• Ranging is correct when all three rods A, P, B appear in one line.
• Rod at P is fixed once alignment is perfect.
• Repeated for more points.

B. Indirect Ranging (Reciprocal Ranging)

• Used when end stations are not intervisible (due to hill, buildings, etc.).

Case I: Hill Obstruction (Reciprocal Ranging)

• Select intermediate points C and D so: C sees B and D, D sees A and C, C aligns C-D-B, then D aligns A-C-D
• Repeat adjustments until A, C, D, B lie on a straight line.

Case II: Long Distance with Obstruction (Random Line Method)

• Suitable when dense vegetation/plantations block direct sighting.
• A random line AB₁ is set from A toward B.
• Chain the random line until B is visible from point B₁.
• Then, the offset (BB₁) is measured and corrected.

Key Points to Remember

• Direct ranging: quick and simple but only if intervisibility exists.
• Indirect ranging: needed for hilly or wooded terrain.
• Tools used: Ranging rods, Line ranger, Theodolite.
• Always done before chaining to ensure accuracy.