Alidade (English spelling)

Japanese: アリダード（英語表記）alidade

An instrument used in plane table surveying, also called an inclinometer. It is a folding, lightweight device consisting of a 27 cm (wooden) or 22 cm (metal) ruler with a metal sight vane attached to each end and a bubble level in the center. This instrument can be used to graphically determine the horizontal angle and indirectly determine the elevation difference and distance between two points. It is often used in topographical and cadastral surveys because it can be placed on a flat plate, a direction line drawn, and the geometrical positional relationship can be determined by the intersection method, and the elevation difference can be easily measured by reading the divisions engraved on the vane. The rear vane has three sighting holes with a diameter of 0.4 to 0.8 mm, and the front vane has a 0.2 mm diameter sighting thread (nylon thread) stretched perpendicular to the bottom of the ruler. The divisions of the vane are in increments of 1/100 of the distance between the vanes. The sighting holes correspond to the divisions 0, 20, and 35, and are called the reference lines. There are also telescope alidades, which have a telescope instead of a sighting plate.

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

Japanese:

平板測量に用いる器械で測斜儀ともいう。長さ 27cm (木製の場合) または 22cm (金属製) の定規の両端に金属製の視準板 sight vaneを取付け，中央に気泡管式の水準器をはめ込んだ折りたたみ式で軽便な器具。この器械で図解的に水平角，間接的に2点間の高低差や距離を求めることができる。これを平板の上に載せて方向線を引き，交会法によって幾何学的な位置関係，視準板の刻まれた分画の読取りによって高さの差を簡単に測定できるので，地形測量や地籍測量によく用いられる。視準板のうち，後方視準板は直径 0.4～0.8mmの視準孔が3個，前方視準板には直径 0.2mmの視準糸 (ナイロン糸) が定規底面に対し垂直に張ってある。視準板の分画は両方の視準板の間隔の 100分の1刻みになっている。視準孔は分画数の0，20，35に対応し，これを基準線という。視準板の代りに望遠鏡をつけた望遠鏡つきアリダードもある。

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