Offsets are of two types _______
📝 Detailed Explanation: Understanding Offsets
In chain surveying, an offset is a lateral distance measured from a main survey line (the chain line) to locate the position of specific features or points of interest within the survey area. These features can include building corners, boundary stones, trees, etc.
Offsets are classified into two main types based on the angle they form with the chain line:
1. Perpendicular Offsets
A perpendicular offset is a measurement taken at a right angle (90°) to the chain line. This is the most common and preferred method because it is the shortest distance from the point to the line, and it simplifies the process of plotting the survey on a map. Instruments like the cross-staff or optical square are used to set out accurate right angles.
2. Oblique Offsets
An oblique offset is a measurement taken at any angle other than 90° to the chain line. These are used when it is impractical or impossible to take a perpendicular offset due to an obstruction. When an oblique offset is taken, both its length and the distance along the chain line to the point of offset must be recorded.
Short vs. Long Offsets
Offsets are also sometimes classified by their length:
- An offset less than 15 meters is generally considered a short offset.
- An offset greater than 15 meters is known as a long offset.
For accurate survey work, it is always desirable to keep offsets as short as possible.