Surveying
Stadia readings used in surveying can be taken with modern instruments such as transits, theodolites, plane-table alidades and levels. When using the stadia measuring method, a stadia rod is held so that it appears between two stadia marks visible on the instrument's reticle. The stadia rod has measurements written on it that can be read through the telescope of the instrument, providing a known length for the distance calculations.
An instrument equipped for stadia work has two horizontal stadia marks spaced equidistant from the center crosshair of the reticle. The interval between stadia marks in most stadia instruments gives a stadia interval factor of 100. The distance between the instrument and a stadia rod can be determined simply by multiplying the measurement between the stadia hairs (known as the stadia interval) by 100.
The instrument must be level for this method to work directly. If the instrument line of sight is inclined, the horizontal and vertical distance components must be determined. Some instruments have additional graduations on a vertical circle to assist with these inclined measurements. These graduated circles, known as stadia circles, provide the value of the horizontal and the vertical measurements as a percentage of the direct stadia measurement.
This system is sufficiently precise for locating topographic details such as rivers, bridges, buildings, and roads when an accuracy of 1/400 is acceptable.
The stadia method of distance measurement is primarily historical for surveying purposes, as distance nowadays is invariably measured by electronic or taping methods. Total station instruments do not have stadia lines marked on the reticle. Traditional methods are still used in areas where modern instruments are not common or by practitioners whose primary task is not surveying with sophisticated instruments.
Read more about this topic: Stadiametric Rangefinding
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