FORE & BACK BEARING WITH CALCULATIONS

 In **prismatic surveying**, **fore bearing (FB)** and **back bearing (BB)** are essential for determining the direction of a survey line. They are always **180° apart**.

### **Definitions**

- **Fore Bearing (FB):** The bearing measured **from a starting station to the next station** in the direction of the survey.

- **Back Bearing (BB):** The bearing measured **from the next station back to the starting station**, in the opposite direction.

### **Formula for Calculating Back Bearing**

If the **Fore Bearing (FB)** is given in **Whole Circle Bearing (WCB)**:

- **BB = FB ± 180°**

  - If **FB < 180°**, then **BB = FB + 180°**

  - If **FB > 180°**, then **BB = FB - 180°**

If the **Fore Bearing (FB)** is given in **Quadrantal Bearing (QB)**:

- **BB is numerically equal to FB**, but:

  - **N is replaced with S**, and **S is replaced with N**

  - **E is replaced with W**, and **W is replaced with E**

### **Example Calculation**

#### **Case 1: Whole Circle Bearing (WCB)**

- Given **FB = 120°**

- **BB = 120° + 180° = 300°**

#### **Case 2: Quadrantal Bearing (QB)**

- Given **FB = N30°E**

- **BB = S30°W**

Fore bearing (FB) and back bearing (BB) play an essential role in **surveying, navigation, and military operations**. Their practical applications include:

### **1. Land Surveying & Mapping**

- Used in **traverse surveying** to determine **directions and locations** of points on land.

- Helps in **boundary demarcation** for **construction projects** and **property disputes**.

### **2. Navigation & Marine Applications**

- Used by **ship navigators** to maintain a straight course using reference points.

- Helps in **avoiding obstacles** at sea by aligning bearings with fixed landmarks.

### **3. Military & Defense Operations**

- Essential for **artillery targeting**, ensuring accuracy in missile strikes.

- Used for **reconnaissance and patrol** routes in unfamiliar terrain.

### **4. Road & Railway Construction**

- Helps in **route alignment** for highways and railway tracks.

- Ensures proper positioning of **tunnels and bridges** during large-scale infrastructure projects.

### **5. Geographical & Environmental Studies**

- Used in **forest surveys** to track wildlife migration paths.

- Helps in **disaster response planning**, such as marking evacuation routes.

### **6. Aviation & Air Traffic Control**

- Pilots use **bearings for navigation** during flights.

- Helps in **runway alignment** and air traffic monitoring.