What is Compass Surveying? Its Type, Uses, Advantages and Disadvantages.

What is Compass Surveying?

Compass Surveying is one of the oldest and traditional techniques of surveying which has served centuries for mankind, this method is surpassed by modern surveying technologies but it remain valuable for its simplicity, affordability, and effectiveness in all aspects.

Compass Surveying Instruments

The various instruments in Compass Surveying are:

  • Prismatic compass
  • Tape
  • Ranging rods
  • Tripod
  • Arrows
  • Plumb Bob

Understanding Compass Surveying: The Core Concepts

  • What it is : In Compass surveying we use specialized compass mainly called as prismatic compass, it is used to measure the distance between two points using Chain, Tape, Laser rangefinder the distance between these two point is called as Magnetic Bearings
  • How it Works: We need to know few things before we know how it works :
  1. Fore Bearing – Fore bearing is also called as forward bearing, it is the bearing measured in the direction of progress of the survey.
  2. Back Bearing – Back bearing is also called as Backward bearing, it is the bearing measured in the direction opposite of the survey.

In the figure below, OA is the survey line to be set out.

  • Fore Bearing (FB) of OA = θ1
  • Back Bearing (BB) of OA = θ2

With the help of Prismatic Compass the surveyor establishes series of station by taking two compass reading in a line segment at each station by help of forbearing and backbearing , the distance between the two station is measured very thoroughly after measuring surveyor uses trigonometric calculation or by graphical method and plot points of each station then they plot them in map or in a plan

Applications of Compass Surveying

Some of the application of compass surveying are :

  • Boundary Surveys: These application of compass surveying are used for Small to Medium Size plots measurement where the property line is small and does not require much accuracy.
  • Route Planning : These application of compass surveying are used to plan or align a route for trails, Pipeline or Roads for easy and short axcess to nearest point.
  • Forestry: These application of compass surveying are used for Mapping trees stands and the easy access paths.
  • Archaeological Surveys: These application of compass surveying are used for Locating and documenting archaeological sites.
  • Navigation: These application of compass surveying are used to Finding your way in remote areas without GPS or other electronic aids (as a backup).

Advantages of Compass Surveying

Some of the advantages of Compass Surveying are :

  • Accessibility: Compasses are easily available in any local store and are relatively available in low cost or inexpensive which make this method of surveying even resourceful.
  • Simplicity: Compass surveying is the simplest method after tape surveying any one can survey after learning it for 15 minutes of training.
  • Ruggedness: As we know compass always shows the north direction align with earth magnetic field even if its raining or in any field Conditions which make them suitable for any rough terrain or condition.

Disadvantages of Compass Surveying

Some of the Disadvantages of Compass Surveying are :

  • Magnetic Declination: Some time Compass shows error due to not perfectly align with true north of earth’s magnetic field.
  • Limited Accuracy: In Compass Surveying Compass readings can be less precise as Compared to modern electronic surveying instruments.
  • Obstacles: While Surveying from compass the reading is affected by many things like Trees, buildings, and other magnetic objects which interfere with compass readings this may cause error on the reading.
  • Complex Calculations: Manual Calculation in the compass surveying causes human error.

Tips for Compass Surveying:

  • Choose the right compass
  • Practice good technique
  • Minimize magnetic interference
  • Record data carefully
  • Verify your work
  • Consider professional training

Types of Compass used in Surveying :

There are mainly two types of compasses are used in Compass Surveying:

  1. Prismatic Compass
  2. Surveyor Compass

Prismatic compass

Prismatic compass: Most common compass Where we measure WCB (Whole Circle Bearing) Where there is a prism for taking observations. It has a circular box which is about 100 mm in diameter. The broad in shape magnetic needle used in a prismatic compass.

Parts of the prismatic compass are as follows: 

  • Cylinder shaped metal box
  • Pivot
  • Magnetic needle
  • Prism
  • Graduation circle
  • Object vane
  • Eye vane
  • Eye silt
  • Eye hole
  • Sunglasses
  • Spring break
  • Reflector mirror
  • Focussing stud
  • Lifting pin
  • Lifting lever

Prismatic Compass Adjustments

There are mainly two types of adjustments in the prismatic compass:

  • Temporary Adjustment (Centering, Levelling, Focussing the prism)
  • Permanent Adjustment (levels, sight vanes, sensitivity of needles, straightness of needles, pivot)

Prismatic Compass Bearing :

Surveyor Compass

A surveyor compass is a type of compass use to measure the measurement of horizontal angles and the bearing of a line of sight.

Parts of a surveyor compass are as follows:

  • Box
  • Lifting lever
  • Pivot
  • Glass top
  • Circular graduated arc
  • Sight vane
  • Jewel bearing
  • Lifting pin
  • Magnetic needle 
  • Rider
  • Metal pin 
  • Object vane 

Surveyor Compass Bearing