The principle of stadia method used in tacheometric surveying is shown in the figure; the distance 'ab', i.e. 'i', refers to ____________.

Explanation:

The Stadia Method:

• The term stadia is now applied to the crosshairs and rods used in making measurements, as well as to the method itself.
• Stadia readings can be taken with most surveying instruments.
• The equipment for stadia measurements consists of a telescope with two horizontal hairs called stadia hairs and a graduated rod called a stadia rod.
• Well adapted to mapping requirements and is widely used for locating details and contour points in topographic surveying.

Stadia Interval Factor:

The ratio of the focal length (f) of the object to the stadia interval (i) is called the stadia interval factor and is designated by the letter K

∴ K = \(\frac{f}{i}\)

For any given instrument, this value remains constant and depends only on the spacing between the stadia hairs.

The most common value of K is 100.