---
title: "Field book and obstacles in chain survey"
subject: "Surveying I"
chapter: 3
key: "semester_3/surveying_i:field-book-and-obstacles"
source: https://www.bctengineer.com/q/semester_3/surveying_i/field-book-and-obstacles
site: BCT Engineering
---

# Field book and obstacles in chain survey

Surveying I · Chapter 3: Chain Survey

- Asked in: 2066 Bhadra, 7 marks
- Video: [OBSTACLES IN CHAIN SURVEYING](https://www.youtube.com/watch?v=VMqa6y1oLi8) — Rajesh J
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/field-book-and-obstacles
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-3

## Question

Make a field book for chain survey. Explain the various types of obstacles in chain survey and the methods to overcome those obstacles.

## Short answer

The field book records chainages and offsets from bottom to top, using single or double red lines. Obstacles: chaining free but vision obstructed is solved by reciprocal ranging; vision free but chaining obstructed by equal perpendiculars (pond) or right-angle method (river); both obstructed by erecting parallel offset lines around the obstacle.

## Answer

#### Field book
The field book is an oblong book (about 20 cm $\times$ 12 cm) in which measurements are recorded in the field. It must be kept neat, and entries must not be erased. The records are made **from the bottom of the page to the top**, so that the page follows the direction in which the line is chained.

#### Types of field book
1. **Single-line field book:** A single red line in the middle of the page represents the chain line. The chainages are written on the line, and the offsets are written on both sides (left and right) of it.
2. **Double-line field book:** Two red lines run along the middle of the page, with a space between them. The chainages are written between these lines, and the left and right offsets are written outside them, with the details drawn.

```text
 Single line type
 | left offset | chainage | right offset |
 |   12 (fence)|   60     |              |
 |             |   45     |  5 (tree)    |
 |             |   0  A   |              |
```

#### Reference sketch of stations
For each station, a small sketch (location sketch) is drawn showing its position, with distances to two or more permanent objects such as corners of buildings, trees or poles.

**Need:**
- The station can be found again if the peg is lost.
- Stations can be re-established for checking or later work.
- It records the name and location of the stations and lines.

#### Sample page of a detailing book
Chain line AB (booked upwards):

| Left (m) | Chainage (m) | Right (m) |
|---|---|---|
| | 100 (B) | |
| 8 (fence corner) | 85 | |
| | 60 | 12 (tree) |
| | 40 | 6 (road edge) |
| 5 (well) | 20 | |
| | 0 (A) | |

#### How offsets are measured and recorded
- The tape is stretched from the chain line to the object at right angles to the line (the perpendicular is set by cross-staff or optical square).
- The chainage at the foot of the offset is read on the chain.
- In the book, the chainage is written on the chain line and the offset length is written on the left or right side, with a short note (fence, tree, building) and a sketch.
- For oblique offsets, the two tie lengths are recorded together with the chainages from which they were taken.

#### Obstacles in chain survey and their remedies
Obstacles are of three types.

**1. Chaining free, vision obstructed (rising ground).** Use **reciprocal ranging**: assistants stand at M1 and N1, each directing the other onto the line towards the far station, until M, N, A and B are in one line.

**2. Vision free, chaining obstructed (pond or river).**
- Pond: erect two equal perpendiculars AC and BD at points A and B on the line, both on the **same side** of it, and measure CD, which equals AB.
- River: at A set out a perpendicular AC and mark D, its mid-point; at C set out CE perpendicular to AC and move along it until E, D and B are in line. Then $AB = CE$.

**3. Both chaining and vision obstructed (building).** Take A and B on the line before the building and erect equal perpendiculars AC and BD. Join CD and extend it beyond the building to E and F, and set out perpendiculars EG and FH equal to AC. G and H are on the original line, and the hidden length $BG = DE$.

```text
    C ------------ D ------------------ E ------------ F
    |              |                    |              |
 ---A--------------B----[ building ]----G--------------H--->
```

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Field book entries are made:
   A. From the top downward
   B. In pencil only on the back
   C. From the bottom of the page upward
   D. Randomly
   Answer: C. Booking follows the progress along the line. (Key point: Booking direction)

2. For a pond, equal perpendiculars AC and BD at A and B are erected. Then AB equals:
   A. AC
   B. BD
   C. AC + BD
   D. CD
   Answer: D. ACDB forms a rectangle. (Key point: Pond obstacle)

3. Which method deals with rising ground between stations?
   A. Reciprocal ranging
   B. Equal perpendiculars
   C. Congruent triangles
   D. Angular measurement with a chain
   Answer: A. Chaining is free but the ends are not intervisible. (Key point: Rising ground)

4. In the building method, the hidden length BG equals:
   A. AC
   B. DE
   C. CD
   D. EF
   Answer: B. Offset lines and rectangle give BG = DE. (Key point: Building obstacle)

## Related in Surveying I

- [Obstacles in chain survey and remedies](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacles-chain-survey) — Surveying I, chapter 3, asked 4×
- [Obstacles; field sketch for detail survey](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aobstacles-and-field-sketch) — Surveying I, chapter 3
- [Chain survey principle and operations](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Achain-principle-and-field-procedure) — Surveying I, chapter 3, asked 2×
- [Principle of chain survey; types of offsets](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Achain-principle-and-offsets) — Surveying I, chapter 3
- [Field procedure of chain surveying](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Afield-procedure-chain-survey) — Surveying I, chapter 3, asked 4×