Distance survey

A survey that measures the distance between two points on the ground, and together with angular surveying, it is a basic element of various ground surveying methods. When triangulation was carried out nationwide during the Meiji and Taisho eras, it was called baseline surveying, and was based on surveying baselines of several kilometers or even tens of kilometers in length at over 10 locations nationwide. When triangulation is carried out independently, a distance survey is required to measure the first side, i.e. the length of the baseline. In multi-gonal surveying, the distance between each node is measured. In the 1970s, the development of electromagnetic rangefinders improved the accuracy of distance surveying beyond that of angular surveying, and trilateration, which measures only the lengths of the three sides of a triangle and not the angle, came to be used as a substitute for triangulation.

Distance measurement methods can be broadly divided into direct distance measurement, indirect distance measurement, and electromagnetic distance measurement. Direct distance measurement is a method in which a graduated ruler is placed between two points to directly determine the distance. For rules, the most accurate Invar ruler, which has almost no expansion or contraction due to temperature changes, as well as steel tape measures or rulers made of steel are used for precision measurements, with a tension of 10 kilograms applied to keep the ruler's expansion and the shape of the suspension curve constant. Other methods used include cloth tape measures and Eslon rulers made of Eslon, but chains and bamboo rulers are no longer used. Indirect distance measurement is also called stadia measurement or tachymetry.

[Yukio Ozaki and Hiromichi Tsuji, November 18, 2016]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

地上の2点間の距離を測る測量で、角測量とともに各種の地上測量法の基本的な要素である。明治・大正時代に三角測量が全国的に行われたときには基線測量といい、数キロメートルあるいは十数キロメートルの基線の長さを全国10余か所に測量して基礎とした。三角測量を独立して行う場合には、最初の1辺すなわち基線の長さを測る距離測量が必要である。多角測量では各節点間の距離測量が行われる。1970年代には電磁波測距儀の発達により距離測量の精度が角測量以上に向上したので、三角形の3辺の長さのみを測量し角度は測量しない三辺測量が三角測量の代用とされるようになった。

　距離測量の方法には大別して直接測距、間接測距、電磁波測距がある。直接測距は、2点間に目盛り尺を当てて直接距離を求める方法で、尺としては、温度変化による伸縮のほとんどない、もっとも精密なインバール尺のほか、鋼製の鋼巻尺あるいは鋼尺が精密な測量には使われ、その際は10キログラムの張力をかけて尺の伸びと懸吊(けんちょう)曲線の形を一定に保つ。そのほか、布巻尺、エスロン製のエスロン尺なども使われるが、チェーンや竹尺はもはや使われない。間接測距はスタジア測量あるいはタキメトリーtachymetryともよばれる。

［尾崎幸男・辻　宏道　2016年11月18日］

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