測(cè)繪專業(yè)英語unit_20-24

1、Unit 20 Understanding the GPS（認(rèn)識(shí) GPS）What Is GPS?（什么是 GPS）The global Positioning System (GPS) operated by the U.S. Department OF Defense (DOD)is a satellite-based system that can be used to locate positions anywhere on the earth.（全球定位系統(tǒng)（GPS），由美國(guó)國(guó)防部【Department OF Defense】管理【operated 運(yùn)轉(zhuǎn)、操作】，是一個(gè)基于人造衛(wèi)星的

2、系統(tǒng)，可以用來在全球任何地方定位）GPS provides continuous (24 hours/day), real-time, 3-dimensional positioning, navigationand timing worldwide.（GPS 提供全世界范圍內(nèi)的全天候，實(shí)時(shí)，三維坐標(biāo)，導(dǎo)航和授時(shí)的功能。）Any person with a GPS receiver can access the system, and it can be used for anyapplication that requires location coordinates.（任何擁有一臺(tái) GPS

3、 接收機(jī)的人都可以使用【access】這套系統(tǒng)，可以應(yīng)用于任何需要位置坐標(biāo)的工作中【be used for 用來做】 ）The GPS system consists of three segments: the space segment: the GPS satellitesthemselves, the control segment, operated by the U.S. military, and the user segment,which includes both military and civilian users and their GPS equipments.（G

4、PS 由【consistof 由組成】三個(gè)部分【segment 部分、節(jié)】組成：太空部分：GPS 衛(wèi)星自己，地面控制部分，由美國(guó)軍方【military 原意軍方的，這里詞性轉(zhuǎn)變了軍方 n.】控制，用戶【user】部分，包括軍方和民用【civilian 民用；civil 民用的civil engineering】用戶和他們的裝備。）Space Segment: The GPS Constellation（太空部分：GPS 星座【或 GPS 星群】）The first GPS satellite was launched by the U.S. Air Force in early 1978.（第

5、一顆 GPS 衛(wèi)星由美國(guó)空軍【Air Force】在 1978 年的早些時(shí)候發(fā)射的）There are now 24 satellites orbiting the earth at an altitude of about 10,900 miles.（現(xiàn)在有24 顆衛(wèi)星在繞地球大約 10900 英里的高度運(yùn)行）The high altitude insures that the satellite orbits are stable, precise and predictable, andthat the satellites motion through space is not aff

6、ected by atmospheric drag.（這么高的高度確保了衛(wèi)星軌道是穩(wěn)定、精確和可知的【predictable 可預(yù)言的、可預(yù)知的】，并且確保了衛(wèi)星穿過太空的運(yùn)行不受到大氣阻力【atmosphericdrag】的影響）There are four satellites in each of 6 orbital planes.（6 個(gè)軌道平面【orbital plane】中每個(gè)有 4 顆衛(wèi)星。）Each plane is inclined 55 degrees relative to the equator, which means that satellites crossthe

7、 equator tilted at a 55 degrees angle.（ 每 個(gè) 平 面 相 對(duì) 于 【relative to】 赤 道 面 傾 斜【incline】55 度，這就意味著這些衛(wèi)星以 55 度角穿過赤道）The system is designed to maintain full operational capability even if two of the 24satellites fail.（這套系統(tǒng)被設(shè)計(jì)成即使 24 顆衛(wèi)星的 2 顆故障也能維持【maintain】全工作能力【operational capability】）These 24 satellites

8、 make up a full GPS constellation.（這 24 顆衛(wèi)星組成了一個(gè)完整的GPS 星座）The GPS satellites are powered primarily by sun-seeking solar panels, with nicad batteriesproviding secondary power.（GPS 衛(wèi)星主要由太陽定向【sun-seeking】太陽能電池板【solar panels】提供動(dòng)力【power 供以動(dòng)力】，鎳鎘蓄電池【nicad batteries】提供備用【secondary 第二的、副的】動(dòng)力）Each GPS satell

9、ite has four atomic clocks on board, only one of which is in use at a time.These highly accurate atomic clocks enable GPS to provide the most accurate timingsystem that exists.（每一個(gè) GPS 衛(wèi)星有四個(gè)原子鐘【on board 在船上，這里就是在衛(wèi)星上的意思】，某一時(shí)刻只有一臺(tái)在使用。這些高精度原子鐘能夠使 GPS 提供最準(zhǔn)確的時(shí)間系統(tǒng)【that exist 持續(xù)、存在】）Control Segment: U.S. D

10、OD Monitoring（控制部分：美國(guó)國(guó)防部監(jiān)控）The U.S. Department Of Defense maintains a master control station at Falcon Air ForceBase in Colorado Springs.（美國(guó)國(guó)防部維持【maintain】了一個(gè)主控站，在科羅拉多斯普林斯【Springs】的佛肯【Falcon 獵鷹】空軍基地）There are four other monitor stations located in Hawaii, Ascension Island, Diego Garciaand Kwajalein.

11、（還有 4 個(gè)監(jiān)控站座落在夏威夷、阿松森島【大西洋】、迭哥加西亞島【印度洋】、卡瓦加蘭島【北太平洋】）The DOD stations measure the satellite orbits precisely.（DOD 站【指 5 個(gè)監(jiān)控站】精確測(cè)量衛(wèi)星軌道）Any discrepancies between predicted orbits and actual orbits are transmitted back to thesatellites.（任何預(yù)報(bào)軌道和實(shí)際軌道之間的偏差【discrepancy 差異】被傳回衛(wèi)星。）The satellites can then broad

12、cast these corrections, along with the other position andtiming data, so that a GPS receiver on the earth can precisely establish the location of eachsatellite it is tracking.（然后衛(wèi)星可以廣播這些改正值連同【along with 連同一起】位置和時(shí)間數(shù)據(jù)一起，以便地球上的 GPS 接收機(jī)可以精確確定它所跟蹤【track】的每個(gè)衛(wèi)星的位置）User Segment: Military and Civilian GPS Us

13、ers （用戶部分：軍方和民用 GPS 用戶）The U.S. military uses GPS for navigation, reconnaissance, and missile guidance systems.（美國(guó)軍方把 GPS 用在導(dǎo)航、偵察和導(dǎo)彈制導(dǎo)【missile guidance】系統(tǒng)上）Civilian use of GPS developed at the same time as military uses were being established,and has expanded far beyond original expectations.（GPS 的民

14、用在軍用建立起之時(shí)就發(fā)展起來了，并且已經(jīng)發(fā)展的遠(yuǎn)遠(yuǎn)超過起初的期望）There are civilian applications for GPS in almost every field, from surveying totransportation to natural resource management to agriculture.（GPS 的民用用途幾乎用在每個(gè)領(lǐng)域，從測(cè)量到交通到自然資源管理到農(nóng)業(yè)）Most civilian uses of GPS, however, fall into one of three categories: navigation,position

15、ing and timing.（然而，GPS 的大部分民用用途，分為【fall into】三種類型【category】：導(dǎo)航、定位和授時(shí)。）How Does GPS Work?（GPS 如何工作）A GPS receiver calculates its position by a technique called satellite ranging, whichinvolves measuring the distance between the GPS receiver and the GPS satellites it istracking.（GPS 接收機(jī)利用一項(xiàng)被稱為衛(wèi)星測(cè)距【 sa

16、tellite ranging】的技術(shù)，計(jì)算它自己的位置，涉及到 GPS 接收機(jī)到它所跟蹤的 GPS 衛(wèi)星的距離測(cè)量）The range (the range a receiver calculates is actually a pseudorange, or an estimate ofrange rather than a true range) or distance is measured as elapsed transit time.（距離（接收機(jī)測(cè)的距離實(shí)際上是偽距，或者說是距離估值，而不是真實(shí)距離）是用傳播時(shí)間來測(cè)的【elapse 流逝 v.】【本句意思是 距離是用測(cè)時(shí)間的方

17、法得到的】）The position of each satellite is known, and the satellites transmit their positions as part ofthe “messages” they send via radio waves.（每個(gè)衛(wèi)星的位置已知，并且衛(wèi)星將它們的位置作為它們用無線電波發(fā)出的“訊文【導(dǎo)航電文】”的一部分傳送【transmit】出去 ）The GPS receiver on the ground is the unknown point, and must compute its positionbased on the

18、information it receives from the satellites.（地面 GPS 接收機(jī)是未知點(diǎn)，必需基于它從衛(wèi)星收到的這些信息計(jì)算它的位置。）The first step in measuring the distance between the GPS receiver and a satellite requiresmeasuring the time it takes for the signal to travel from the satellite to the receiver.（測(cè)量GPS 接收機(jī)和衛(wèi)星的第一步，要求【require】測(cè)出【它把信號(hào)來傳播

19、】從衛(wèi)星到接收機(jī)的信號(hào)【signal】傳播時(shí)間。）Once the receiver knows how much time has elapsed, the travel time of the signalmultiplies the speed of light (because the satellite signals travel at the speed of light,approximately 186,000 miles per second) to compute the distance.（ 一 旦 接 收 機(jī) 知 道 用【elapse 流逝】了多少時(shí)間，用信號(hào)的傳播時(shí)

20、間乘【multiply】上光速（因?yàn)樾l(wèi)星信號(hào)以光速傳播，大約【approximately】186,000 英里每秒）來計(jì)算距離。）Distance measurements to four satellites are required to compute a 3-dimensional (latitude,longitude and altitude) position.（計(jì)算一個(gè)三維（緯度、精度和高程）位置需要【berequired to 被需要】4 顆衛(wèi)星的距離值）In order to measure the travel time of the satellite signal,

21、the receiver has to know whenthe signal left the satellite and when the signal reached the receiver.（為了測(cè)出衛(wèi)星信號(hào)的傳播時(shí)間，接收機(jī)需要知道信號(hào)是什么時(shí)候離開衛(wèi)星的和什么時(shí)候到達(dá)接收機(jī)的 ）Knowing when the signal reaches the receiver is easy, the GPS receiver just “checks” itsinternal clock when the signal arrives to see what time it is.（確定

22、信號(hào)到達(dá)接收機(jī)的時(shí)間容易，GPS 接收機(jī)只需在信號(hào)到達(dá)時(shí)“檢查”自己內(nèi)置的鐘，看看是什么時(shí)間）But how does it “know” when the signal left the satellite?（但是怎樣“知道”信號(hào)何時(shí)離開衛(wèi)星的呢？）All GPS receivers are synchronized with the satellites so they generate the same digitalcode at the same time.（所有 GPS 接收機(jī)與衛(wèi)星是同步的【synchronize 同步 v.】，因此它們?cè)谕粫r(shí)間產(chǎn)生同樣的信號(hào)碼）When the

23、 GPS receiver receives a code from a satellite, it can look back in its memorybank and “remember” when it emitted the same code.（當(dāng) GPS 接收機(jī)收到一個(gè)從衛(wèi)星來的碼時(shí)，它可以在它的內(nèi)存條【memory bank】中回憶【回溯】并“記起”它發(fā)出【emit因?yàn)榻邮諜C(jī)不向衛(wèi)星發(fā)射信號(hào)，因此這里應(yīng)翻譯為產(chǎn)生】的相同碼）This little “trick” allows the GPS receiver to determine when the signal left

24、the satellite.（這個(gè)小小的“技巧”【trick 竅門、惡作劇、詭計(jì)】使得 GPS 接收機(jī)能夠確定信號(hào)是何時(shí)離開衛(wèi)星的）Once the receiver has the distance measurements, its basically a problem of geometry.（一旦接收機(jī)測(cè)出了距離，基本上【basically】就只有幾何上的問題了）If it “knows” where the four satellites are, and how far it is from each satellite, it cancompute its location t

25、hrough trilateration. Heres an illustration of how it works.（如果知道了 4 顆衛(wèi)星的位置，距每顆衛(wèi)星的距離【it 指接收機(jī)而不是衛(wèi)星】，就可以通過三邊測(cè)量來計(jì)算它的位置。這里有個(gè)例子【illustration 例子】說明它如何工作的）The GPS receiver “l(fā)ocks on” to one satellite and calculates the range to be 12,000 miles.（GPS 接收機(jī)“鎖定”一顆衛(wèi)星并計(jì)算出距離為 12,000 英里）This fact helps narrow the re

26、ceiver location down, but it only tells us that we aresomewhere on a sphere which is centered on the satellite and has a 12,000 mile radius.（這把接收機(jī)的位置限定【narrow 使變窄，這里就是限制的意思】下來，但是它只能告訴我們?cè)谝粋€(gè)以這個(gè)衛(wèi)星為中心，半徑 12,000 英里的球面上）Many of the locations on that sphere are not on earth, but out in space.（這個(gè)球面的許多位置不在地球

27、上，而在太空中）Now, consider that the receiver picks up a signal from a second satellite and calculates therange between the receiver and the satellite to be 10,000 miles.（現(xiàn)在，考慮這個(gè)接收機(jī)從第二顆衛(wèi)星獲得【pick up】一個(gè)信號(hào)，計(jì)算出接收機(jī)到這顆衛(wèi)星的距離是 10,000英里）That means we are also somewhere on a sphere with a 10,000 mile radius with th

28、e secondsatellite at the center.（這就意味著我們也在一個(gè)以第二顆衛(wèi)星為中心、半徑 10,000 英里的球面上的某處【somewhere】）We must, therefore, be somewhere where these two spheres intersect.（因此，我們肯定在這兩個(gè)球面相交【intersect】的某處。）When the two spheres intersect, a circle is formed, so we must be somewhere on that circle.（當(dāng)這兩個(gè)球面相交時(shí)，一個(gè)圓圈形成了，因此我們肯定

29、在這個(gè)圓圈的某處）If the receiver picks up another satellite, says at 11,000 miles away, another sphere isformed, and there are only two points where the three spheres intersect.（如果接收機(jī)“拾取”了另一個(gè)衛(wèi)星，比方說【say 比方說、假定】11,000 英里以外，另一個(gè)球面形成了，三個(gè)球面相交只有兩個(gè)交點(diǎn)）Usually the receiver can discard one of the last two points becau

30、se it is nowhere near theearth.（通常接收機(jī)可以丟棄【discard】最后這兩點(diǎn)中的一個(gè)點(diǎn)，因?yàn)樗x地球差的遠(yuǎn)【nowhere near】）So, were left with one point which is the location of the GPS receiver. In practice, a fourthmeasurement is needed to correct for clock error.（這樣我們留下一個(gè)點(diǎn)，它是 GPS 接收機(jī)的位置。在實(shí)際當(dāng)中，需要第四個(gè)觀測(cè)值來修正時(shí)間誤差【不能翻譯成鐘誤差，因?yàn)殓娬`差中文上是指衛(wèi)星和接收機(jī)的

31、鐘的誤差】）Uuit21 Understanding the GPS (II) 認(rèn)識(shí) GPS(II)GPS Error Sources (GPS 誤差來源)There are many sources of possible errors that will degrade the accuracy of positioncomputed by a GPS receiver.（有許多或然誤差【possible error】來源，這種誤差會(huì)降低【degrade】GPS 接收機(jī)計(jì)算的位置的準(zhǔn)確度）【that 從句修飾 errors】The travel time of GPS satellite

32、signals can be altered by atmospheric effects; when a GPSsignal passes through the ionosphere and troposphere it is refracted, causing the speed ofthe signal to be different from the speed of a GPS signal in space.（GPS 衛(wèi)星信號(hào)的傳播時(shí)間會(huì)因大氣影響而改變【alter】；當(dāng) GPS 信號(hào)穿過電離層【ionosphere】和對(duì)流層【troposphere】時(shí)會(huì)發(fā)生折射【refrac

33、t】，因?yàn)樾盘?hào)速度與在太空中信號(hào)的速度不同。）II)Sunspot activity also causes interference with GPS signals.（太陽黑子活動(dòng)也對(duì) GPS 信號(hào)產(chǎn)生干擾【interference 干涉、干擾】）Another source of error is measurement noise, or distortion of the signal caused byelectrical interference or errors inherent in the GPS receiver itself.（另一個(gè)誤差源是測(cè)量噪聲，或者是由于電干擾

34、【electrical interference】或 GPS 接收機(jī)自己固有的誤差引起的信號(hào)失真【distortion】）【即，電干擾和接收機(jī)固有誤差 都是失真原因】Errors in the ephemeris data (the information about satellite orbits) will also cause errorsin computed positions, because the satellites werent really where the GPS receiver“thought” they were (based on the informati

35、on it received) when it computed the positions.（星歷數(shù)據(jù)（關(guān)于衛(wèi)星軌道的信息）誤差也會(huì)引起位置的誤差，因?yàn)楫?dāng)計(jì)算位置時(shí)，衛(wèi)星不真正地在接收機(jī)“認(rèn)為”它們?cè)诘牡胤剑ɑ谒邮艿男畔⑺溃㏒mall variations in the atomic clocks (clock drift) on board the satellites can translate tolarge position errors; a clock error of 1 nanosecond translates to 1 foot or 0.3 meters use

36、rerror on the ground.（衛(wèi)星原子鐘內(nèi)的很小的變化【variation 變奏、變化】 鐘漂【drift漂流；應(yīng)該是鐘偏 clock offset】）能轉(zhuǎn)化成很大的位置誤差；一納秒【nanosecond】的鐘差能造成 1 英尺或 0.3 米的地面用戶誤差）Multipath effects arise when signals transmitted from the satellites bounce off a reflectivesurface before getting to the receiver antenna.（當(dāng)從衛(wèi)星發(fā)射的信號(hào)在到達(dá)接收機(jī)天線【antenn

37、a 天線】之前，被一個(gè)反射面【reflective surface】反射【bounce off】時(shí)，多路徑效應(yīng)【Multipath effect】出現(xiàn)了【arise】）When this happens, the receiver gets the signal in straight line path as well as delayed path(multiple paths). The effect is similar to a ghost or double image on a TV set.（當(dāng)這種情況發(fā)生時(shí)，接收機(jī)接收直線路徑來的信號(hào)，也【as well as】接收延遲路線（

38、多路徑）來的信號(hào)。其效果與電視的重影【ghost】或重像類似）（How to Reduce GPS Errors（如何減小 GPS 的誤差）Youve probably heard people talk about getting 2 to 5 meters accuracy with a GPSreceiver, or even centimeter or millimeter accuracy.（你可能聽說過有人說 GPS 接收機(jī)可以達(dá)到 2 到 5 米的準(zhǔn)確度，甚至是厘米或毫米級(jí)精度）Is there a way to cancel out the errors and get sat

39、isfied accuracy?（ 有 方 法 低 償 【cancelout】誤差并獲得滿意的精度嗎？）The answer is yes, but the level of accuracy depends on the type of equipment you areusing.（回答是肯定的，但是準(zhǔn)確度的級(jí)別依賴于你使用的裝備的類型）The following discussion describes a technique used to achieve 2 to 5 meters accuracyusing mapping (resource) grade receivers.（下

40、面的討論描述了一種用于繪圖（資源）級(jí)【grade】接收機(jī)的技術(shù)，能夠獲得 2 到 5 米的準(zhǔn)確度）Some mapping grade receivers are even capable of sub-meter accuracy, but the increasedaccuracy comes at a price.（一些繪圖級(jí)的接收機(jī)甚至能夠達(dá)亞米級(jí)精度，但是精度的提高是以很高代價(jià)帶來的【at a price 以很高代價(jià) adv.】Survey grade receivers are the most accurate, capable of centimeter or even mil

41、limeteraccuracy, depending on the equipment, but they use more advanced techniques to achievethis level of accuracy and, naturally, are more expensive.（ 測(cè) 地 級(jí) 接 收 機(jī) 最 精 確 ， 憑【depend on】裝備能夠達(dá)到厘米甚至是毫米級(jí)精度，但是它們是使用更先進(jìn)的技術(shù)才得到這樣的精度水平，自然地，就更昂貴。）Recreational grade receivers usually can receive real-time diffe

42、rential corrections, but theycannot store a file that can be differentially corrected using post-processing methods.（休閑【Recreational 娛樂的、休閑的】級(jí)的接收機(jī)通?？梢越邮諏?shí)時(shí)差分改正，但是它們不能存儲(chǔ)文件，【that 從句修飾 file】以便可以用后處理【post-processing 后處理】方法差分【differentially】改正。）Differential Correction（差分改正）Differential correction is a met

43、hod used to reduce the effects of selective available (SA)and other sources of GPS positioning error (differential correction cannot correct formultipath or receiver error; it counteracts only the errors that are common to bothreference and roving receivers).（差分改正是一種用來減小 選擇可用性政策(SA)影響和其它 GPS 定位誤差源 的

44、方法（差分改正不能修正多路徑效應(yīng)或接收機(jī)誤差；它只能抵消【counteract 抵消】基準(zhǔn)接收機(jī)【reference receiver】和流動(dòng)接收機(jī)【roving receiver】所共有的誤差）It requires, in addition to your “roving” GPS receiver, a GPS receiver on the ground in aknown location to act as a static reference point.（這需要除了【in addition to 除之外】你的“流動(dòng)”GPS 接收機(jī)之外 一個(gè) GPS 接收機(jī)在地面上一個(gè)已知的位置

45、擔(dān)當(dāng)【act as】靜態(tài)【static】參考點(diǎn)）【如果要直譯的話，可以兩邊加破折號(hào)把中間的句子夾起來】This type of setup is often called a GPS base station. Since the base station “knows” whereit is, it can compute the errors in its position calculations (in reality, it computes timingerrors) and apply them to any number of roving receivers in the s

46、ame general area.（這種設(shè)備經(jīng)常被稱為 GPS 基準(zhǔn)站。由于基準(zhǔn)站“知道”在哪兒，它就可以計(jì)算它自己的位置誤差（實(shí)際上，它是計(jì)算 定時(shí)誤差【timing error】），并將它們應(yīng)用于【apply to將應(yīng)用于】許多【any number of 許多】同一區(qū)域的流動(dòng)接收機(jī)）This requires that the base and rover receivers “see” the same set of satellites at the sametime.（這需要基準(zhǔn)接收機(jī)和流動(dòng)接收機(jī)同時(shí)“看到”【鎖定】相同一批衛(wèi)星）The base station, dependin

47、g upon how it is configured, can correct roving GPS receiverdata in one (or both) of two ways.（基準(zhǔn)站，依照如何配置【configure】，可以用兩種中的一種方法（或同時(shí)用兩種）對(duì) GPS 流動(dòng)接收機(jī)的數(shù)據(jù)進(jìn)行修正）in the first method, called real-time differential correction or real-time differential GPS(DGPS), the base station transmits (usually via radio

48、link) error correction messages toother GPS receivers in the local area.（第一種方法，稱為實(shí)時(shí)差分改正或?qū)崟r(shí)差分 GPS（DGPS），基準(zhǔn)站發(fā)射（通常經(jīng)由【via 經(jīng)由、通過】無線電聯(lián)系）誤差改正信息到其它當(dāng)?shù)氐?GPS 接收機(jī)）In this case, the positions you read on your GPS receiver while you are out collecting dataare the corrected positions.（這樣，當(dāng)你外出收集數(shù)據(jù)時(shí)在你的 GPS 接收機(jī)上讀出的位置

49、就是改正后的位置。） the second method, called post-processed differential correction, is performed on acomputer after the roving receiver data are collected.（第二種方法，稱為后處理差分改正，在流動(dòng)站數(shù)據(jù)收集完后經(jīng)由計(jì)算機(jī)完成的【perform 執(zhí)行、完成】）While you are out in the field collecting data, the positions you read on your roving GPSreceiver are

50、 uncorrected.（當(dāng)你在野外收集數(shù)據(jù)時(shí)，你在 GPS 流動(dòng)接收機(jī)上讀出的位置是未經(jīng)修正的【uncorrected】）It is not until you take the rover files back to the office and process them using differentialcorrection software and data from the base station file, that you get corrected positions.（直到你把流動(dòng)站文件帶回辦公室并利用差分改正軟件和基準(zhǔn)站的文件數(shù)據(jù)進(jìn)行處理，你才能得到改后位置）The

51、base station file contains information about the timing errors.（基準(zhǔn)站文件包括同步誤差信息）This information allows the differential correction software to apply error corrections tothe roving receiver file during processing.（這種信息可以在處理時(shí)使差分改正軟件把誤差改正施于流動(dòng)接收機(jī)文件上。）【apply to 把施于】Since the base and rover receivers have

52、to “see” the same set of satellites at the same time,the base file has to start before the rover file starts, and end after the rover file ends (a basestation is normally set up to track all satellites in view, insuring that it will “see” at leastthe four satellites that the roving receiver is using

53、 to compute positions).（由于基準(zhǔn)站接收機(jī)和流動(dòng)站接收機(jī)必需同時(shí) “看到 ”同一組衛(wèi)星，基準(zhǔn)站文件必需開始于流動(dòng)站文件之前，結(jié)束于流動(dòng)站文件之后（基準(zhǔn)站通常設(shè)置為跟蹤所有視野內(nèi)的衛(wèi)星，以保證至少“看到”流動(dòng)站接收機(jī)用來計(jì)算位置的 4 顆衛(wèi)星）Post-processed differential correction, then, requires both base and rover receivers that arecapable of collecting and storing files.（后處理差分改正，要求基準(zhǔn)站接收機(jī)和流動(dòng)接收機(jī)都能收集和存儲(chǔ)文件。）M

54、ost recreational grade receivers cannot collect and store files that can be differentiallycorrected.（多數(shù)休閑級(jí)接收機(jī)不能收集和存儲(chǔ)可以用來差分改正的文件）How Accurate Is GPS?（GPS 準(zhǔn)確度如何？）The accuracy that can be achieved using GPS depends on the type of equipment used, thetime of observation, the positions of the satellites b

55、eing used to compute positions, themodel and the software you used.（使用 GPS 可以達(dá)到的準(zhǔn)確度依賴于使用裝置的類型、觀測(cè)時(shí)間、用來計(jì)算位置的衛(wèi)星的位置、你所使用的模式和軟件）In general, recreational and mapping grade receivers using C/A code without differentialcorrection are accurate to between 30 and 100 meters.（大體上講【In general】，使用 C/A碼沒有差分改正的休閑和繪圖級(jí)接收機(jī)精度在 30 到 100 米之間。）Many people using recreational grade receivers dont realize they cannot get highlyaccurate readings using them autonomousl