| 单词 | optical square |
| 释义 | > as lemmasoptical square optical square n. Surveying an instrument used to establish lines of sight at right angles to each other by using light bent through a right angle by mirrors or a prism. ΘΚΠ the world > the earth > earth sciences > geography > map-making > surveying > [noun] > surveying instruments > for laying off lines at right angles optic square1809 optical square1853 1853 W. T. Brande Dict. Sci., Lit. & Art (ed. 3) 1205/1 For the purpose of tracing the perpendicular, the simple cross-staff may be employed; but the instrument called the optical square (which is merely a small, shallow, circular box containing the two principal glasses of the sextant fixed at an angle of 45°) will effect the purpose with greater accuracy. 1950 J. Clendinning Princ. & Use Surv. Instruments (1972) ii. 10 The optical square..is somewhat more convenient than the cross staff for setting out a line at right angles to another. 1984 A. Bannister & S. Raymond Surveying (ed. 5) ii. 13 The prismatic type of optical square employs a pentagonal-shaped prism. < as lemmas |
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