測繪工程專業(yè)英語課文翻譯(14-17)

1、Unit14 Datums, Coordinates and Conversions （已知坐標轉(zhuǎn)換）A datum is the mathematical model of the Earth we use to calculate the coordinates and elevations on any map , chart, or survey system . Geodetic datum s define the size and shape of the Earth and the origin and orientation of the coordinate systems

2、 used to map the Earth . Hundreds of different datum s have been used to frame position descriptions since the first estimates of the Earths size were made by Aristotle . But all coordinates reference some particular set of numbers for the size and shape of the Earth . For example, the Global Positi

3、oning System (GPS) is based on the World Geodetic System 1984 (WGS-84) . Many countries use their own datums when they make their maps and surveyswhat we call local datums .（基準是我們用來計算任何地圖、海圖或測量系統(tǒng)的坐標和海拔的地球的數(shù)學(xué)模型。大地測量數(shù)據(jù)定義了地球的大小和形狀，以及用于映射地球的坐標系的起源和方向。數(shù)以百計的不同的數(shù)據(jù)已被用于幀位置描述，因為第一次估計地球的大小是由亞里士多德。但是所有坐標都引用了地球的

4、大小和形狀的一些特定的數(shù)字集。例如，全球定位系統(tǒng)（GPS）是基于世界大地測量系統(tǒng)1984（WGS-84）。許多國家使用自己的數(shù)據(jù)時，他們使他們的地圖和調(diào)查，我們稱之為局部基準。）Horizontal and Vertical Datums（水平和垂直數(shù)據(jù)）In geodesy two types of datums must be considered: a“ Horizontal Datum ”for location ,which for m s the basis for the computations of horizontal control surveys in which th

5、e curvature of the Earth is considered and a“ Vertical Datum ”for elevation or to which elevations are referred . Vertical control networks provide elevations with reference to a surface of constant gravity force called the geoid . Almost all maps and charts use mean sea level (geoid) for elevation

6、. But they might use any of over hundred different horizontal position datums . One example of horizontal datum is a mathematical surface called a reference ellipsoid with which positional information (latitude and longitude) is referenced to . T he coordinates for points in specific geodetic survey

7、s and triangulation networks are computed from certain initial quantities (datums) . Sometimes, a map will have more than one grid on it .Normally,each grid is for a different datum .（在大地測量中的兩種基準必須考慮：“水平面”位置，為M S為基礎(chǔ)，計算平面控制測量中，被認為是地球的曲率和“垂直基準”，海拔高程或被稱。垂直控制網(wǎng)絡(luò)提供海拔參考的表面重力稱為大地水準面的恒定重力。幾乎所有的地圖和海圖都使用平均海平面（

8、大地水準面）進行高程測量。但他們可能使用任何超過百種不同的水平位置的基準。一個例子的水平基準是一個數(shù)學(xué)表面稱為參考橢球與位置信息（緯度和經(jīng)度）是參照。他在特定的大地測量坐標點和三角網(wǎng)是由一定的初始量計算（基準）。有時，地圖上會有一個以上的網(wǎng)格，通常每個網(wǎng)格都有不同的數(shù)據(jù)。）Horizontal datum and coordinates: A horizontal datum is a surface of constant values that forms the basis for the computations of horizontal control surveys . In a

9、 horizontal datum a reference ellipsoid is used as a mathematical approximation of the shape of the Earth . Five parameters are required to define a horizontal datum : two to specify the dimensions of the ellipsoid, two to specify the location of an initial point ( origin ) , and one to specify the

10、orientation (i .e ., north) of the coordinate system . For exa m ple , the radius and flattening of the ellipsoid selected for the computations to specify the dimensions of the ellipsoid , the longitude and latitude of an initial point ( origin ) to specify the location and an azimuth of a line ( di

11、rection ) to so m e other (triangulation ) station to specify the orientation . A change in any of these quantities affects every point on the datum . For this reason , while positions within a system are directly and accurately reliable, data such as distance and azimuth derived from computations i

12、nvolving geodetic positions on different datum s will be in error in proportion to the difference in the initial quantities .（水平基準和坐標：水平基準面是恒定值的表面，是水平控制測量計算的基礎(chǔ)。在水平基準面中，參考橢球用作地球形狀的數(shù)學(xué)近似。需要五個參數(shù)來定義一個水平基準：兩個指定的橢球的尺寸，兩個指定的初始點（原點）的位置，和一個指定的坐標系的取向（北，北）。為例子說明，半徑和橢球選擇指定橢圓的尺寸計算壓扁，經(jīng)度和緯度的初始點（原點）指定的位置和線的方位（方向），M

13、E其他（三角）站指定的方向。任何數(shù)量的變化都會影響數(shù)據(jù)的每一點。出于這個原因，而在一個系統(tǒng)中的位置是直接和準確可靠的，如距離和方位的計算來自不同的基準數(shù)據(jù)的大地測量位置的數(shù)據(jù)將在錯誤的比例在初始數(shù)量的差異。）The two main horizontal datums used in the U .S . are the North American Datum of 1927(N AD27) and the North American Datum of 1983 (NAD83) . In 1986 , NAD83 replaced NAD27 because the latter was

14、found to be not accurate enough to support modern positioning activities that occur in highly accurate electronic measurement system s and satellitebased positioning system s . NAD83 is an earth-centered datum and relies on an ellipsoid (and other constants) of the Geodetic Reference System of 1980

15、( G RS80 ) . It is important to note that GPS position calculations are based on the WGS84 datum ( World Geodetic System of 1984 ) , which for all practical purposes is identical to GRS80 . In China , Xian Geodetic Coordinate System 1980 is used as a horizontal datum in which the initial point ( ori

16、gin ) is in Shanxi Province .（兩主水平基準用于U。S。1927是北美基準（N ad27）和1983的北美基準（NAD83）。1986、NAD83取代NAD27因為后者被認為是不夠準確的支持現(xiàn)代定位活動發(fā)生在高度精確的電子測量系統(tǒng)和衛(wèi)星定位系統(tǒng)。是以地球為中心的NAD83基準和依賴于一個橢球（和其他常數(shù)）1980的大地測量參考系統(tǒng)（G RS80）。需要注意的是，GPS位置的計算是基于WGS84基準重要（1984世界大地坐標系統(tǒng)），這對于所有的實際目的是相同的GRS80。在中國，1980西安坐標系作為水平基準的起始點（原點）是山西。）Vertical datum an

17、d heights: The zero surface , to which elevations or heights are referred ,is called a vertical datum . From previous text we know the geoid is an equipotential surface of the Earth gravity field that most closely approximates the mean sea surface . At everypoint the geoid surface is perpendicular t

18、o the local plumb line . It is therefore a natural reference for heights measured along the plumb line . Heights referred to the geoid are called orthometric heights , which stand in contrast to geodetic (ellipsoidal) heights, which refer to the ellipsoid . Because we cannot directly see the geoid s

19、urface, we cannot actually measure the heights above or below the geoid surface . We must infer where this surface is by making gravity measurements and by modeling it mathematically . For practical purposes , we assume that at the coastline the geoid and the MSL surfaces are essentially the same .

20、Nevertheless, as we move inland we measure heights relative to the zero height at the coast, which in effect means relative to MSL . Therefore w e use mean sea level as a plane upon which w e can reference or describe the heights of features on , above or below the ground .（垂直基準面和高程：被稱為高程或高程的零曲面稱為垂直

21、基準面。從前面的文本中我們知道，大地水準面是地球重力場的一個等位面，與平均海平面最接近。在每一個點的大地水準面垂直于當(dāng)?shù)劂U垂線。因此，它是沿著垂線測量高度的自然基準。高度稱為大地水準面稱為正高高地站在相反，大地（橢球）的高度，并參考橢球。因為我們不能直接看到大地水準面，所以我們不能實際測量大地水準面上面或下面的高度。我們必須通過重力測量和數(shù)學(xué)建模來推斷這個表面的位置。為了實用的目的，我們假設(shè)在海岸線的大地水準面和MSL的表面基本上是相同的。然而，當(dāng)我們搬到內(nèi)陸我們測量的高度相對于零高度在海岸，這意味著相對于MSL。因此，使用平均海平面作為一個平面上，可以參考或描述的高度，上面或下面的地面。）E

22、levations are not required for most parcel mapping applications . However, since GPS is a 3D ( actually 4D ) measuring device, elevations are available for every point . As mentioned earlier, the GPS-derived elevation refers to the ellipsoid ( ellipsoidal height) , not the mean sea level (orthometri

23、c height) .(大多數(shù)包裹映射應(yīng)用程序不需要海拔。然而，由于GPS是一個三維（實際上4D）測量裝置，海拔可用于每一點。如前所述，得出的高程GPS指橢球（大地高），不是平均海平面（正高）。)Conversions(轉(zhuǎn)換)A coordinate conversion or transformation is the process of bringing a coordinate fro m one defined coordinate system ( or zone) into another through a series of algorithms based on the l

24、atitude/ longitude position of the point . Coordinate systems based on the same datum retain a perfect mathematical relationship , allowing coordinate values to be precisely transformed between them .(坐標轉(zhuǎn)換或轉(zhuǎn)換是將一個定義坐標系（或區(qū)域）的坐標通過一系列基于緯度/長度的算法引入到另一個坐標系中的過程 點的位置度?；谕换鶞实淖鴺讼当Ａ粢粋€完美的數(shù)學(xué)關(guān)系，使坐標值在它們之間精確地轉(zhuǎn)換。)Bu

25、t the coordinates for a point on the Earths surface in one datum will not match the coordinates from another datum for that same point . The differences occur because of the different ellipsoids used and the probability that the centers of each datums ellipsoid is oriented differently with respect t

26、o the Earths center . A grid shift exists between datum s because each datum has a different origin .(但是在一個基準面上，地球表面上某個點的坐標與另一個基準點的坐標不匹配。差異時，因為不同的橢球我們 和每個基準橢球的中心相對于地球中心的方向不同的概率?；鶞拭嬷g存在網(wǎng)格偏移，因為每個數(shù)據(jù)具有不同的 聯(lián)發(fā)。)A datum conversion is the process of bringing coordinate values referenced to one defined datum

27、 into another datum system s . Complete datum conversion is based on seven parameter transformations that include three translation parameters, three rotation parameters and a scale parameter . Simple three parameter conversion between latitude, longitude, and height in different datums can be accom

28、plished by conversion through Earth- Centered , Earth Fixed XYZ Cartesian coordinates in one reference datum and three origin offsets that approximate differences in rotation , translation and scale .(基準轉(zhuǎn)換是將基準數(shù)據(jù)的坐標值轉(zhuǎn)換為另一基準系統(tǒng)的過程。完整的基準轉(zhuǎn)換是基于七參數(shù)變換 包括三個平移參數(shù)，三個旋轉(zhuǎn)參數(shù)和一個刻度參數(shù)。簡單的三參數(shù)轉(zhuǎn)換之間的緯度，經(jīng)度，和在不同的基準高度可以完成 通過

29、轉(zhuǎn)換地球為中心，地球固定XYZ笛卡爾坐標在一個基準基準和三原點偏移的近似差異，旋轉(zhuǎn)，平移和規(guī)模。)Unit15 Map Projection(投影地圖)Map projections are attempts to portray the surface of the Earth or a portion of the Earth on a flat surface . Some distortions of conformality , distance , direction , scale, and area always result from this process . Some

30、projections minimize distortions in some of these properties at the expense of maximizing errors in others . So m e projections are attempts to only mode rately distort all of these properties . No projection can be simultaneously conformal and area-preserving .(地圖投影是在平面上描繪地球或部分地球表面的投影。保形、距離、方向、規(guī)模和地

31、區(qū)總是有些扭曲，結(jié)果F 只讀此過程。一些預(yù)測最大限度地減少這些屬性的扭曲，犧牲最大限度地在別人的錯誤。所以我的預(yù)測是試圖模式地歪曲一切 這些屬性。沒有投影可以同時保形和保面積。)Conformality: When the scale of a map at any point on the map is the same in any direction, the projection is conformal . Meridians (lines of longitude) and parallels (lines of latitude) intersect at right angle

32、s . Shape is preserved locally on conformal maps .(協(xié)調(diào)：當(dāng)規(guī)模的地圖，在地圖上的任何一點在任何方向上的投影是一樣的，形。經(jīng)線（經(jīng)線）和緯線（緯線）相交于 直角。保形映射局部保持形狀。)Distance: A map is equidistant when it portrays distances from the center of the projection to any other place on the map .(距離：當(dāng)?shù)貓D描繪從投影中心到地圖上任何其他位置的距離時，地圖是等距的。)Direction: A map prese

33、rves direction when azimuths ( angles fro m a point on a line to another point) are portrayed correctly in all directions .(方向：地圖保留方向時方位角（角度從線路上的一個點到另一點）被描繪在所有方向正確。)Scale: Scale is the relationship between a distance portrayed on a m ap and the same distance on the Earth .(尺度：尺度是一個距離的M AP和地球上的相同距離之間

34、的關(guān)系。)Area: When a map portrays areas over the entire map so that all mapped areas have the same proportional relationship to the areas on the Earth that they represent, the m ap is anequal-area map .(區(qū)：當(dāng)一個地圖描繪區(qū)域在整個地圖上，所有映射的區(qū)域具有相同的比例關(guān)系的地區(qū)在地球，他們表示，M AP是平等的地區(qū)地圖。)Classification of Map Projection(地圖投影分類)

35、Map projections are generally classified into four general classes according to common properties ( cylindrical vs . conical, conformal vs . area-preserving , etc .) , although such schemes are generally not mutually exclusive .(地圖投影一般分為四個一般類，根據(jù)共同的屬性（圓柱比。圓錐，共形對。區(qū)域保存等），雖然這種方案屬 而不是相互排斥。)Cylindrical pr

36、ojections result from projecting a spherical surface onto a cylinder . A cylindrical projection can be imagined in its simplest for m as a cylinder that has been wrapped around a globe at the equator . If the graticule of latitude and longitude are projected onto the cylinder and the cylinder un w r

37、apped , then a grid-like pattern of straight lines of latitude and longitude would result . T he meridians of longitude would be equally spaced and the parallels of latitude would re main parallel but m ay not appear equally spaced any more . In reality cylindrical map projections are not so simply

38、constructed . The three aspects of the cylindrical projections are as follows:(柱面投影是將球面投影到圓柱體上的結(jié)果。一個圓柱投影可以想象的最簡單的M作為一個圓柱體已被包裹在一個地球 赤道。如果經(jīng)度和緯度的經(jīng)緯網(wǎng)投影到圓柱和圓柱非W敲擊，然后網(wǎng)格狀的經(jīng)度和緯度的直線模式研究 ULT。經(jīng)度的經(jīng)度是相等的，緯度的平行度是平行的，但不會出現(xiàn)同樣的距離。實際上柱面投影是 不是那么簡單的構(gòu)造。圓柱投影的三個方面如下：) Tangent or secant to equator is termed regular , or no

39、rmal . When the cylinder is tangent to the sphere contact is along a great circle (the circle formed on the surface of the Earth by a plane passing through the center of the Earth ) . In the secant case, the cylinder touches the sphere along two lines, both s m all circles ( a circle formed on the s

40、urface of the Earth by a plane not passing through the center of the Earth) .(切線或割線到赤道被稱為規(guī)則，或正常。當(dāng)氣缸的球體接觸切線沿大圓（圈形成表面的地球的飛機經(jīng)過 克通過地球中心。在割線的情況下，圓柱體沿兩條線接觸球體，兩個球體都是圓的（一個在地球表面上形成的圓，而不是通過 雖然地球的中心）。) Tangent or secant to a meridian is the transverse aspect . W hen the cylinder upon which the sphere is projec

41、ted is at right angles to the poles, the cylinder and resulting projection are transverse .(子午線的切線或割線是橫切面。當(dāng)球體被投射的圓柱體與兩極成直角時，圓柱體和由此產(chǎn)生的投影是橫向的。 ) Tangent or secant to another point on the globe is called oblique . W hen the cylinder is at so m e other, non-orthogonal, angle with respect to the poles, t

42、he cylinder and resulting projection is oblique .(切線或割線到地球上的另一個點稱為斜。當(dāng)氣缸在M E，非正交的，相對于極角，氣缸和投影是義務(wù) 神游。)Conic projections result fro m projecting a spherical surface onto a cone . When the cone is tangent to the sphere contact is along a small circle . In the secant case , the cone touches the sphere al

43、ong two lines, one a great circle, the other a small circle . In the Conical Projection the graticule is projected onto a cone tangent, or secant, to the globe along any small circle ( usually a mid-latitude parallel) . In the nor m al aspect ( which is oblique for conic projections), parallels are

44、projected as concentric arcs of circles, and meridians are projected as straight lines radiating at uniform angular intervals fro m the apex of the flattened cone .Conic projections are not widely used in mapping because of their relatively small zone of reasonable accuracy . The secant case , which

45、 produces two standard parallels , is more frequently used with conics . Even then , the scale of the map rapidly becomes distorted as distance from the correctly represented standard parallel increases . Because of this problem ,conic projections are best suited for maps of mid-latitude regions, es

46、pecially those elongated in an east- west direction . The United States meets these qualifications and therefore is frequently mapped on conic projections .(球面投影到圓錐上的圓錐投影結(jié)果。當(dāng)圓錐體與球面相切時，接觸點是一個小圓圈。在割線的情況下，圓錐體接觸球體 翁兩行，一一大圈，另一小圈。在圓錐投影的經(jīng)緯網(wǎng)投影到圓錐切線或割線，在小繞地球（通常是一個mid-l 緯度平行）。在不平行的方面（斜向圓錐投影），平行線被投影為圓的同心圓弧，子午線

47、被投影為直線 在平錐頂點上均勻的角距，由于其相對合理的精度范圍較小，圓錐映射在制圖中的應(yīng)用并不廣泛。割線的情況下 生產(chǎn)雙標準緯線，更頻繁地使用圓錐曲線。即使這樣，地圖的規(guī)模迅速變得扭曲，從正確的表示標準并行增加距離 锿.由于這個問題，圓錐投影最適合中緯度地區(qū)的地圖，特別是那些在東西方向拉長的地圖。美國滿足這些資格 ND經(jīng)常被映射在圓錐投影。)Azimuthal ( Planar ) projections result fro m projecting a spherical surface onto a plane .When the plane is tangent to the sphe

48、re contact is at a single point on the surface of the Earth . In the secant case , the plane touches the sphere along a small circle if the plane does not pass through the center of the Earth , when it will touch along a great circle .(方位角（平面）投影是將一個球面投影到一個平面上，當(dāng)平面與球面相切時，在地球表面的一個點上。在美國證券交易委員會 如果飛機不穿過地

49、球的中心，當(dāng)它沿著一個大圈旋轉(zhuǎn)時，飛機就會沿著一個小圓圈接觸球體。)Miscellaneous projections include unprojected ones such as rectangular latitude and longitude grids and other examples of that do not fall into the cylindrical, conic, or azimuthal categories .(雜項預(yù)測包括未計劃的如矩形經(jīng)緯網(wǎng)格和其他的例子，不落入圓柱形，圓錐形，或方位的類別。)Choosing a projection is to d

50、eter mine: Location , Size and Shape . These three things determine where the area to be mapped falls in relation to the distortion pattern of any projection. One“traditional”rule described by Maling ( Maling , 1992 ) says:(選擇一個投影是阻止我的：位置，大小和形狀。這三件事決定要映射的區(qū)域與任何投影的變形模式有關(guān)。一個“傳統(tǒng)”的規(guī)則描述的Maling（馬嶺，1992）說：)

51、A country in the tropics asks for a cylindrical projection .(熱帶地區(qū)的一個國家需要一個圓柱投影。)A country in the temperate zone asks for a conical projection .(溫帶地區(qū)的國家要求錐形投影。)A polar area asks for an azimuthal projection .(極性區(qū)域要求方位投影。)Implicit in these rules of thu m b is the fact that these global zones m ap into

52、the areas in each projection w here distortion is lo west: Cylindricals are true at the equator and distortion increases toward the poles . Conics are true along so m e parallel so m e w here between the equator and a pole and distortion increases a w ay fro m this standard . Azimuthals are true onl

53、y at their center point, but generally distortion is worst at the edge of the map . For a particular map-use the map may need to be conformal, equal area, or some compromise of these . In some cases, such as navigation , conformality is absolutely necessary . In statistical mapping , equivalence is

54、necessary . T he final projection choice would see m to be a fairly straight forward function of minimized distortion and special properties .（在這四M B規(guī)則隱含的事實是，這些全球區(qū)M AP為每個投影在變形區(qū)羅西：cylindricals在赤道向兩極和失真的增加是真實的。圓錐曲線是真實的，我所以我在平行的赤道和極和失真增加的方式從這一標準間。azimuthals是真的只有在他們的中心點，但一般的失真是最嚴重的在地圖的邊緣。對于一個特定的地圖使用的地圖可

55、能需要是共形，平等的地區(qū)，或一些妥協(xié)。在某些情況下，如導(dǎo)航、協(xié)調(diào)是絕對必要的。在統(tǒng)計映射中，等價是必要的。最后的投影選擇將看到M是一個相當(dāng)直的函數(shù)最小化失真和特殊屬性。）Universal Transverse Mercator (UTM)(通用橫軸墨卡托投影（UTM）Mercator projection was invented in 1569 by Gerardus Mercator ( Flanders) graphically .The properties of this projection are: (1) Conformal . (2) Meridians unequally

56、 spaced , distance increases a way fro m equator directly proportional to increasing scale . (3) Loxodromes or rhumb lines are straight . (4) Used for navigation and regions near equator .(墨卡托投影是在1569發(fā)明的赫拉爾杜斯·墨卡托（佛蘭德）圖形。該投影的特點是：（1）適形。（2）子午線不等距，距離增大的一種方式 赤道與尺度成正比。（3）方位線或恒向線是直的。（4）用于赤道附近的導(dǎo)航和區(qū)域。)T

57、he accuracy of Transverse Mercator projections quickly decreases fro m the central meridian . Therefore , it is strongly recommended to restrict the longitudinal extent of the projected region to + / - 10 degrees fro m the central meridian .(橫墨卡托投影精度迅速下降，從中央子午線。因此，強烈建議限制的投影區(qū)域的縱向范圍為+ / 中央子午線10度)The U

58、TM system applies the Transverse Mercator projection to mapping the world , using 60 pre-defined standard zones to supply parameters . UTM zones are six degrees wide . Each zone exists in a North and South variant .（UTM系統(tǒng)采用墨卡托投影映射的世界，使用60個預(yù)先定義的標準區(qū)提供參數(shù)。UTM區(qū)六度寬。每個區(qū)域存在于北境 南方變種。）Unit16 Gravity Measurmen

59、t(重力測量)As known from daily experience , the most conspicuous force present on the surface of the Earth is gravity . Gravity is the force that pulls things towards the center of the Earth .Gravity affects almost everything in our lives . From clocks to hydroelectric dams, from the tides of the oceans to plant life, gravity plays an important role . Gravity governs our height and shape and keeps us fro m falling off the surface of the Earth .(從日常經(jīng)驗中得知，地球表面最顯著