# Stadia Definitions for Land Surveyors

stadia- 1 A method of surveying in which distances and elevations are obtained by observing the interval on a graduated, upright rod (stadia rod) intercepted by two parallel horizontal lines (stadia hairs or stadia wires) in a surveyor’s transit set up at a distance from the rod. Also called “stadia survey.” See also tachymetry, tacheometry. 2 In ancient Greece and Rome, a unit of linear measure equal to about 607 feet (185 meters).

stadia constant [LEVELING]—The constant which is multiplied by the stadia interval to obtain the length of a sight in meters. Also, the constant by which the sum of the stadia intervals of all sights of a run is converted to the length of the run in kilometers. When feet, yards, or rods are used, the resulting lengths will be in feet and kilofeet or yards and kiloyards.

stadia reduction methods—Inclined stadia measurements are more frequent than are horizontal measurements. Each inclined measurement is reduced to give the horizontal distance and difference in elevation. Trigonometric formulas involving the vertical angle and rod intercept have been derived to make this reduction. Stadia tables and/or diagrams are available to ease the computation, as are specially prepared stadia slide rules. Instruments equipped with a stadia circle or a Beaman arc have multipliers on the vertical circle for both H and V, thus eliminating the need to measure vertical angles. In the so-called “self-reading” stadia instruments, the normal stadia cross hairs are replaced by curved lines which are variably spaced as the line of sight is inclined. These curved lines are constructed and based on inclined-sight stadia formulas. Another variation is a reticule with straight lines, with one fixed and the other free to move with the telescope inclination by a suitably designed and formula-based cam.

stadia rod—A graduated rod used to measure the distance from the observation point to the place where the rod is positioned. The method of reading is by observing the length of the rod subtended by the distance between the stadia hairs when these are fixed, or by noting the space between the stadia hairs when they are adjusted to cover a certain definite interval on the rod; also called “stadia.”

stadia slide rule—A slide rule which has, in addition to the ordinary scale of numbers (logarithms of the distances), two scales especially constructed for stadia work, one consisting of values of log cos²a and the other of log 1/2 sin 2a for different values of a. On some rules, the values of a range from 0° 34′ to 45°; on others, from 0° 03′ to 45°. In some forms the horizontal distance is read directly; in others the horizontal correction (1-cos²) or sin2 is given.