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Stadia marks, also called stadia lines or stadia hairs, are crosshairs on the
A typical surveyor's instrument
reticle
A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscop ...
of a theodolite
A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building an ...
or other surveying instrument that allow stadiametric rangefinding
Stadiametric rangefinding, or the stadia method, is a technique of measuring distances with a telescopic instrument. The term stadia comes from a Greek unit of length '' Stadion'' (equal to 600 Greek feet, '' pous'') which was the typical length ...
.
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
A reticle, or reticule also known as a graticule, is a pattern of fine lines or markings built into the eyepiece of an optical device such as a telescopic sight, spotting scope, theodolite, optical microscope or the screen of an oscilloscop ...
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
Levelling or leveling (American English; see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartog ...
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
Stadiametric rangefinding, or the stadia method, is a technique of measuring distances with a telescopic instrument. The term stadia comes from a Greek unit of length '' Stadion'' (equal to 600 Greek feet, '' pous'') which was the typical length ...
*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 l ...
*Theodolite
A theodolite () is a precision optical instrument for measuring angles between designated visible points in the horizontal and vertical planes. The traditional use has been for land surveying, but it is also used extensively for building an ...
*Dumpy level
A level is an optical instrument used to establish or verify points in the same horizontal plane in a process known as levelling, and is used in conjunction with a levelling staff to establish the relative height levels of objects or marks. It is ...
*Plane table
A plane table (plain table prior to 1830) is a device used in surveying site mapping, exploration mapping, coastal navigation mapping, and related disciplines to provide a solid and level surface on which to make field drawings, charts and maps. ...
*Levelling rod
Levelling or leveling (American English; see spelling differences) is a branch of surveying, the object of which is to establish or verify or measure the height of specified points relative to a datum. It is widely used in geodesy and cartog ...
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