Ranging Rod,Arrows,Ranging Pole

 

Ranging Rod —

• Ranging rod is a surveying instrument used for ranging (locating) points on a straight line.

• It is generally made of wood, steel, or fibre.

• Standard length is usually 2 m or 3 m.

• It is generally 25–30 mm in diameter and has a pointed metal shoe at the bottom.

• It is painted in alternate red and white or black and white bands, usually about 20 cm long.

• The coloured bands make the rod clearly visible from a distance.

• It is used in chain surveying to mark survey stations and intermediate points.

• For long distances, ranging rods may be used with ranging poles or flags for better visibility. 

Arrows (Chain Surveying)

• Arrows ko chain surveying mein distance ki measurement ke दौरान chain lengths count karne ke liye use kiya jata hai.
• Ye generally steel wire ke bane hote hain.
• Ek arrow ki length lagbhag 40 cm hoti hai.
• Ek set mein aam taur par 10 arrows hote hain.
• Measurement complete hone par arrows ko collect karke chain lengths count ki jaati hain.  

Ranging Pole — 

• Ranging pole is a surveying instrument used for ranging straight lines.
• It is generally made of wood or steel.
• Its usual length is about 2–3 m.
• It is painted in alternate red and white bands for easy visibility.
• A pointed metal shoe is provided at the bottom for fixing it into the ground.
• It is used to mark survey stations and intermediate points during chain surveying. 

Line Ranger —

• Line ranger is a surveying instrument used for ranging a straight line between two points.
• It is used to locate an intermediate point on the straight line joining two survey stations.
• It works on the principle of reflection of light using two mirrors or prisms.
• It is useful when the end points are not intervisible or when accurate ranging is required.
• It is quicker and more accurate than ordinary visual ranging for suitable conditions.

Offset Rod —

• Offset rod is a surveying instrument used for measuring and setting out offsets from the survey line.
• It is generally about 3 m long.
• It is made of wood or metal.
• It has a pointed end for fixing it into the ground.
• It is usually graduated and painted in alternate black and white/red and white bands.
• It is mainly used in chain surveying for locating details such as buildings, roads, fences, etc. 

Open Cross Staff — 

• Open cross staff is a surveying instrument used for setting out perpendicular offsets from a chain line.
• It is mainly used in chain surveying.
• It consists of a vertical staff with two pairs of sighting slits.
• The two pairs of slits are placed at right angles (90°) to each other.
• It is used to locate points on the ground that are perpendicular to the survey line.
• It is simple and easy to use, but less accurate than an optical square. 

Three Types of Cross-Staff

Type	Shape of Head	Angles Measured	Main Feature
Open Cross-Staff	Square or Round	90° only	Simplest and most common form; features two pairs of lines at right angles.
French Cross-Staff	Octagonal (8-sided)	45° and 90°	A hollow brass box with slits on all eight sides for more flexible angle marking.
Adjustable Cross-Staff	Cylindrical	Any angle	Features two graduated cylinders that rotate against each other using a vernier scale

Types of Optical Squares

• Mirror Optical Square:
  • Features two mirrors placed inside a small metal box.
  • The mirrors are fixed at an exact angle of 45 degrees to each other.
  • Due to the laws of reflection, a ray of light that hits these mirrors undergoes a total deviation of 90 degrees (2 × 45°).
• Prism Square:
• A more modern, accurate version that replaces the mirrors with a pentagonal prism (five-sided glass prism).
• The two reflecting surfaces inside the prism are permanently manufactured at a 45-degree angle.
• Because the angle is built into the solid glass, it never goes out of adjustment, making it highly reliable in the field. 

Optical Square 

Perpendiculars can be set out on a survey line with much greater precision using an optical square compared to the previously described cross-staff. This instrument works on the Principle of Reflection of light rays striking a mirror.

Optical squares are of the following three types:

1. Cylindrical Optical Square 
2. Indian Optical Square
3. Prism Square 

---

(i) Cylindrical Optical Square

• (a) Instrument: Inside a round metal box approximately 5 cm in diameter and 12 cm in height, two vertical mirrors
  

  $A$
  and
  

  $B$
  are fixed in such a way that the angle between them is exactly
  

  ${45}^{\circ }$
  (Figure 2.10).

• Mirror A: Wholly silvered glass (called Index Glass).
• Mirror B: Top half is silvered (called Horizon Glass), and the bottom half is ordinary/un-silvered glass.
• Slits: Eye slit (
  

  $E$
  ), window slit (
  

  $G$
  ) directly opposite to it, and a third rectangular slit (
  

  $F$
  ) positioned at a right angle to the line joining
  

  $E$
  and
  

  $G$
  . 

Let the light ray

$PA$

coming from point

$P$

make an angle

$\alpha$

with mirror

$A$

, therefore:

$\angle DA{a}_1=\alpha$

---

Mathematical Proof (From Image 2)

• Then,
  
  
  
  (Law of Reflection)
• But,
  
  
  
  (Position of mirrors)
• 
  
  
  
  
  
  
  
  
  
• Again,
  
  
  
  
  
  (Law of Reflection) 
• Therefore,
  
  
  
  
  
  
  
  
  
  
  
• But,
  
  
  
  
  
Now, considering


:


$\angle ADB={180}^{\circ }-\angle DAB-\angle ABD$



$\angle ADB={180}^{\circ }-[{180}^{\circ }-2\alpha ]-[2\alpha -{90}^{\circ }]$



$\angle ADB={180}^{\circ }-{180}^{\circ }+2\alpha -2\alpha +{90}^{\circ }$



$\therefore \angle ADB={90}^{\circ }$
Hence, if the images of

$P$
and

$O$
appear in a single vertical line, the lines coming from these points will be perpendicular to each other.    
Indian Optical Square
1. Introduction (परिचय)
• Purpose: It is a surveying instrument used to drop a perpendicular line (offset at 90°) from a target object onto a chain line.
• Material: It is a simple and common instrument made of brass.
---
2. Construction / Components (बनावट)
• Shape: It is a hollow trapezoidal (wedge-shaped) brass box with a depth of 3 cm.
• Faces:
  • Open End (
    

    $PQRS$
    ): The wider side is completely open and faces the target object.
  • Closed End: The side opposite to the open end is completely closed.
• Mirrors (
  

  $M_1$
  &
  

  $M_2$
  ): Two mirror strips are fixed on the inner slanted faces at a specific angle of
  

  ${45}^{\circ }$
  to each other.
• Rectangular Holes (
  

  $A$
  &
  

  $B$
  ): Located in the upper part of both mirrors to look through.
• Handle: Attached to the bottom of the box for holding the instrument. 


Working Procedure (प्रयोग विधि)
• Holding the Instrument:
  • If the target object is to the right of the chain line
    

    $\to$
    Hold the instrument in the left hand.
  • If the target object is to the left of the chain line
    

    $\to$
    Hold the instrument in the right hand.
• Steps for Finding the Perpendicular Foot:
  1. Positioning: The observer stands on the chain line and points the open face (
     

     $PQRS$
     ) towards the target object.
  2. Sighting: Look through rectangular hole
     

     $A$
     or
     

     $B$
     at the ranging rod fixed on the chain line.
  3. Movement: Move forward or backward along the chain line.
  4. Alignment: Stop when the image of the chain-line rod and the image of the target rod align exactly in a straight line inside the mirror.
  5. Ground Marking: The exact location of the instrument at this moment is the foot of the perpendicular. Transfer this point to the ground using a plumb bob or by dropping a pebble.