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Stadia marks, also called stadia lines or stadia hairs, are crosshairs on the reticle of a theodolite or other
A typical surveyor's instrument reticle has two pairs of stadia marks. One pair are on the horizontal centreline and the other on the vertical cross hair. Each functions in the same manner and are placed for measuring on either axis.
The stadia marks are set a specific length apart. This length is chosen so that there is a fixed, integer ratio between the difference of the rod readings and the distance from the telescope to the rod. This ratio is known as the ''stadia constant'' or ''stadia interval factor''. Thus the formula for distance is
:
where
*
*
*
For example, a typical stadia mark pair are set so that the ratio is 100. If one observes a vertical length on a stadia rod, rule or levelling rod with the telescope and sees that the rod spans 0.500 m between the marks (the ''stadia interval''), then the horizontal distance from the instrument to the rod is:
: 0.500m x 100 = 50 m.
In the adjacent image, the upper stadia mark is at 1.500 m and the lower at 1.345 m. The difference is 0.155 m. Thus the distance from the instrument to the levelling rod is:
: 0.155 x 100 = 15.5 m.
surveying
Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...
instrument that allow stadiametric rangefinding.
Etymology
The term stadia mark derives from the obsolete unit of distance, the stadion, derived from the Greek measurement of a stadium.Early Units of Measurement and the Nautical Mile, Commander Alton B. Moody, U.S.N.R. (U.S. Navy Hydrographic Office), pp 162-170, The Journal of Navigation / Volume 5 / Issue 3 / July 1952 . Several different stadia were defined, such as the Greek stadion and Egyptian stadion.Usage
A typical surveyor's instrument reticle has two pairs of stadia marks. One pair are on the horizontal centreline and the other on the vertical cross hair. Each functions in the same manner and are placed for measuring on either axis.
The stadia marks are set a specific length apart. This length is chosen so that there is a fixed, integer ratio between the difference of the rod readings and the distance from the telescope to the rod. This ratio is known as the ''stadia constant'' or ''stadia interval factor''. Thus the formula for distance is
:
where
*
*
*
For example, a typical stadia mark pair are set so that the ratio is 100. If one observes a vertical length on a stadia rod, rule or levelling rod with the telescope and sees that the rod spans 0.500 m between the marks (the ''stadia interval''), then the horizontal distance from the instrument to the rod is:
: 0.500m x 100 = 50 m.
In the adjacent image, the upper stadia mark is at 1.500 m and the lower at 1.345 m. The difference is 0.155 m. Thus the distance from the instrument to the levelling rod is:
: 0.155 x 100 = 15.5 m.
See also
* Stadiametric rangefinding *Tacheometry
Tacheometry (; from Greek for "quick measure") is a system of rapid surveying, by which the horizontal and vertical positions of points on the earth's surface relative to one another are determined without using a chain or tape, or a separate le ...
* Theodolite
* Dumpy level
* Plane table
* Levelling rod
References
Sources
*Raymond Davis, Francis Foote, Joe Kelly, ''Surveying, Theory and Practice'', McGraw-Hill Book Company, 1966 LC 64-66263 *{{cite web, title=The Stadia, author=James B. Calvert, publisher=University of Denver, date=August 12, 2003, url=https://mysite.du.edu/~jcalvert/astro/stadia.htm, archivedate=2013-05-20, archiveurl=https://web.archive.org/web/20130520172828/https://mysite.du.edu/~jcalvert/astro/stadia.htm Measuring instruments Surveying