Stadia survey; tachymetry

Japanese: スタジア測量 - スタジアそくりょう（英語表記）stadia survey; tachymetry

Also called visual distance surveying. A method of indirect distance measurement used in topographical surveying. A transit or level telescope is used to sight a stadia (staff) in front of the telescope, and the length of the staff between two stadia hairs (equally spaced above and below the crosshairs) and the vertical angle are measured. The result is multiplied by a constant (stadia constant) to determine the diagonal distance, horizontal distance, and relative height. Since there are stadia tables with calculated constants, it is easy to obtain the measurement results, but the accuracy is lower than that of direct distance measurements using a steel tape measure or electromagnetic range finder. A transit used exclusively for stadia surveying is called a tachymeter. Another method is to measure the arc minutes from one end of a staff (called a subtense bar) placed horizontally on a tripod with a transit, and then use the measured angle to determine the distance. In stadia surveying using plane table surveying (stadia method), a rod with two metal plates (plates) painted red and white on the top and bottom, attached at a regular interval, is used as a scale, and the distance between the plates of the scale rod set up at the measurement point is read in fractions of the alidade to determine the distance.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

視距測量ともいう。地形測量に用いられる間接距離測量法の一つ。トランシットやレベル (水準儀) の望遠鏡で，前方に立てた標尺 stadiaを視準し，望遠鏡の視野内で，十字線の上下に等間隔に張った2本のスタジア線 stadia hairではさんだ標尺の長さと，そのときの鉛直角をはかり，一定の定数 (スタジア定数) を乗じて，斜距離や水平距離，比高を求める。定数が計算されているスタジア表があるので，測定結果を出すのは簡単であるが，鋼巻尺や電磁波測距儀による直接測距に比し精度は劣る。スタジア測量専用のトランシットをタキメータ tachymeterという。三脚の上に水平に乗せた一定長さの標尺 (サブテンスバー subtense barという) をトランシットで端から端まで分角をはかり，その測角から距離を出す方法もある。平板測量で行うスタジア測量の場合 (スタジア法) は，赤白のペンキを上下に塗った金属板 (覘板〈てんばん〉) を一定間隔に2枚取付けた棒を標尺とし，測定点に立てた標尺の覘板の間隔をアリダードの分画で読み，距離を求める。

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