Stadia (method)
From Wikipedia, the free encyclopedia
Stadia is a technique of measuring distances with a telescopic instrument. The term stadia comes from a Greek unit of length.
Stadia readings, used in surveying, can be taken with today’s modern instruments such as transits, theodolites, and levels. When using the stadia measuring method, a measurement rod is held so that it appears between two stadia lines visible on the instrument's reticle. A transit or level equipped for stadia work has two additional horizontal cross wires spaced equidistant from the center of the telescope. The interval between stadia wires in most stadia instruments gives a vertical ratio of 1:100. The distance to a rod can be read directly simply by multiplying the rod measurement between the stadia hairs by 100. This system is sufficiently precise for locating topographic details such as rivers, bridges, buildings, and roads to a reasonable accuracy.
The stadia method is based upon the principle that in similar triangles homologous sides are proportional. The stadia method is good when accuracy of 1/400 is acceptable. In a transit there are 3 horizontal wires and 1 vertical wire. The center horizontal wire is used for normal sights. The top and bottom wires are the stadia lines. The principle is relatively simple, at a distance of 100 feet the difference between the top and bottom wires on the rod is 1 foot. The transit or level must be horizontal for this formula to work.
[edit] External links
- The Stadia
- "Technique of Fire", Ch. 5 of US Army FM 23-11: 90mm Recoilless Rifle, M67 — demonstrates stadiametric rangefinding in an anti-tank weapon sight
