【正文】 to be familiar with the meanings of certain basic terms before describing angle anddirection measurement.（在描述角度和方向測量之前，有必要熟悉【be familiar with 熟悉】幾個【certain某些】基本術語的含義【meaning】）The terms discussed here have reference to the actual figure of the earth.（這里討論的這些術語與地球的真實形狀有關【have reference to 與……有關】）Basic Terms（基本術語）A vertical line at any point on the earth’s surface is the line that follows the direction of gravityat that point.（地球表面任一點的垂線是指這點上沿著重力的方向的線【可譯為：地球表面任一點的垂線方向是過該點的重力方向】）It is the direction that a string will assume if a weight is attached at that point and the stringis suspended freely at the point. （如果在這點上用線懸掛一個重物，當線自由【即無干擾】靜止【suspended暫停的、懸浮的】時，這條線所呈現(xiàn)【assume 呈現(xiàn)】的方向即重力方向。）At a given point there is only one vertical line.（在給定的一個點上只有一條垂線。）A horizontal line at a point is any line that is perpendicular to the vertical line at the point. （一點上的水平線是垂直【perpendicular 垂直的】于過該點的垂線的直線。）At any point there are an unlimited number of horizontal lines.（過任一點的水平線有無數(shù)【unlimited】條。）A horizontal plane at a point is the plane that is perpendicular to the vertical line at the point.（過一點的水平面是垂直于過該點的垂線的平面）There is only one horizontal plane through a given point.（過給定的一個點只有一個水平面）A vertical plane at a point is any plane that contains the vertical line at the point.（過一點的豎直面是包含【contain】過該點的垂線的任一平面）There are an unlimited number of vertical planes at a given point.（過給定的一點有無數(shù)個豎直面）Horizontal Angle and Vertical Angle（水平角和豎直角）A horizontal angle is the angle formed in a horizontal plane by two intersecting vertical planes, ora horizontal angle between two lines is the angle between the projections of the lines onto a horizontalplane.（水平角是指在一個水平面內(nèi)由兩相交【intersect 相交 v.】的豎直面形成的角，或者說，兩條線之間的水平角是這兩條線在水平面上的投影線的夾角）For example, observations to different elevation points B and C from A will give the horizontal angle∠bac which is the angle between the projections of two lines (AB and AC) onto the horizontal plane.（例如，在 A 點觀測不同高度的 B 和 C 點，其水平角∠bac 是由 AB 和 AC 兩條線在水平面上的投影構成的）It follows that, although the points observed are at different elevations, it is always the horizontalangle and not the space angle that is measured (Figure 1).（由此得出結論【It follows that 由此得出結論】，雖然被觀測的點在不同的高度上，測出的總是水平角而不是空間角。）The horizontal angle is used primarily to obtain relative direction to a survey control point, ortopographic detail points, or to points to be set out.（水平角主要【primarily】用來由聯(lián)測控制點獲得相對方向，或者地形測量碎部點、或者放樣點【or to points to be set out 應該是 or points to be set out才對吧？？？direction to a survey control point、topographic detail points、points to be set out并列都是 obtain 的賓語。】）A vertical angle is an angle measured in a vertical plane which is referenced to a horizontal lineby plus (up) or minus (down) angles, or to a vertical line from the zenith direction.（豎直角是在一個豎直面內(nèi)參考于【reference 參考】水平線的正（仰）角或負（俯）角，或者相對于一個天頂方向的垂線的角）Plus and minus vertical angles are sometimes referred to as elevation or depression angles, respectively.（正負豎直角有時分別【respectively 分別地】被稱為仰角【elevation angle】或俯角【depression angle】）A vertical angle thus lies between 0176。 and 177。90176。.（豎直角位于【lie 位于】0～90 度之間）Zenith is the term describing points on a celestial sphere that is a sphere of infinitely large radiuswith its center at the center of the earth.（天頂方向是一個術語，用來描述在天球【celestial sphere天球】上的點，天球是一個半徑無限【infinitely 無限地】大的球，其中心在地球中心。）The zenith is an angle measured in a vertical plane downward from an upward directed vertical linethrough the instrument.（天頂距是一個在豎直面內(nèi)從一個過儀器的被定向為向上的豎直方向線 向下測量的角。）It is thus between 0176。 and 180176。.（它的范圍是從 0 到 180 度）Obviously the zenith angle is equal to 90176。 minus the vertical angles.（顯然，天頂距等于 90 度減去豎直角）Vertical angles or zeniths are used in the correction of slope distance to the horizontal or in heightdetermined.（豎直角或天頂距用于斜距化平距的改正或者高程的測量）For the most part, the instrument used in the measurement of angles is called a transit or theodolite,although angles can be measured with clinometers, sextants (hydrographic surveys), or passes.（在極大程度上【for the most part】，用來測角的工具被稱為經(jīng)緯儀，雖然角度可以用傾斜儀【一種測量物體隨時間的傾斜變化和鉛垂線隨時間變化的儀器】、六分儀（用于海道測量）、或羅盤儀來測）The theodolite contains a horizontal and vertical circles of either glass or silver.（經(jīng)緯儀有一個玻璃的或鍍銀的水平度盤和豎直度盤）The horizontal and vertical circles of theodolite can be linked to circular protractors graduated from0176。 to 360176。 in a clockwise manner set in horizontal and vertical plane.（經(jīng)緯儀的水平度盤和豎直度盤與順時針刻【graduate】了 0 到 360 度刻劃的圓分度器【circular protractor】相連）The horizontal circle is used when measuring or laying off horizontal angles and the vertical circleis used to measure or lay off vertical angles or zenith angles.（測或撥水平角時用水平度盤，測或撥豎直角或天頂距時用豎直度盤【lay off 翻譯為撥、放樣的意思】）Usually the units of angular measurement employed in practice are degrees, minutes, and seconds, thesexagesimal system.（通常角度測量法【angular measurement 角度測量法】使用的單位是六十進制【sexagesimal六十進制的】的度、分、秒）Angle Measurement （角度測量）A horizontal angle in surveying has a direction or sense。 that is, it is measured or designed to theright or to the left, or it is considered clockwise or counterclockwise.（在測的水平角有方向【direction、sense 這里都是方向的意思】，就是說【that is】它是向左測還是向右測，或者是說，順時針測還是逆時針測）In the above figure, the angle at A from B to C is clockwise and the angle from C to B is counterclockwise.（如上圖所示，在 A 點由 B 到 C 就是順時針角，而從 C 到 B 就是逆時針角）With the theodolite set up, centered, and leveled over at station A, then a simple horizontal anglemeasurement between surveying point B, A and C would be taken as follows:（經(jīng)緯儀在 A 點安置、對中、整平后，在 B、A 和 C 測量點間的簡單的水平角測量可以按下列步驟進行：）⑴Commencing on, say, “face left”, the target set at survey point B is carefully bisected and thereading on horizontal scale is 25176。.（著手，說【示意】，“盤左”，【用豎絲】將 B 點的目標仔細分中，水平度盤讀數(shù)為 25 度）⑵The upper plate clamp is released and telescope is turned clockwise to survey point C. The readingon horizontal circle is 75176。（水平度盤制動螺旋松開，順時針轉(zhuǎn)動望遠鏡至 C 點，水平度盤讀數(shù) 75 度）⑶The horizontal angle is then the difference of the two directions