【正文】 n et al.,2001a). Thus making seamless DGPS positioning available across the world. The advantage is that costly infrastructure is no longer needed, however, the user has to rely on the US Department of Defence (DoD) for GPS data, on a global infrastructure of active GPS reference stations,and on NASA’s JPL for the corrective information. Realtime productsThe Internetbased Global Differential GPS (IGDG) system aims at realtime precise position determination of a single receiver either stationary or mobile, anywhere and anytime. The concept of Precise Point Positioning (PPP) was introduced in the early 1970s, for more details refer to the key article by Zumberge et al. (1997). Precise Point Positioning utilizes fixed precise satellite clock and orbit solutions for single receiver positioning. This is a key to standalone precise geodetic point positioning with cm level precision.Over the past several years the quality of the Rapid IGS satellite clock and orbit products has improved to the cm level. Today the IGS Rapid service provides the satellite clock/orbit solutions within one day, with almost the same precision as the precise final IGS solutions (IGS, 2004).A good agreement between satellite clock error estimates produced by 7 Analysis Centers (AC) contributing to the IGS is reached. These estimates agree within – ns or 3 – 6cm. Currently IGS orbits with a few decimeter precision, can be made available in (near) realtime. Ultrarapid/predicted ephemerides are available twice each day(at 03:00 and 15:00 UT), and cover 48 hours. The first 27 hours are based on observations, the second part gives a predicted orbit. It allows one to obtain high precision positioning results in the field using the IGS products. of corrective informationTraditionally, DGPScorrections are broadcast over a radiolink from reference receiver to rover. With IGDG, corrections are disseminated over the open Internet. The user can access the very modest correction data stream using a (direct and) permanent network connection, or over the public switched telephone network (PSTN), possibly using an Asynchrone Digital Subscriber Line (ADSL). For a moving user access is possible using mobile (data) munication by cellular phone (possibly General Packet Radio Service (GPRS) or the Universal Mobile Telemunication System (UMTS) in future) or satellite phone. For mercial use three Inmarsat geosynchronous munication satellites are utilized to relay the correction messages on their Lband global beams. The three satellites (at 100?W (Americas), 25?E (Africa), 100?E (Asia Pacific)) provide global coverage from latitude ?75?to +75?.2 InternetBased Global Differential GPSIn Spring 2001, the Jet Propulsion Laboratory (JPL) of the National Aeronautics Space Administration (NASA) launched Internetbased Global Differential GPS (IGDG). Compared with traditional Differential GPS (DGPS) services, the position accuracy improves by almost one order of magnitude. An accuracy of 10 cm horizontal and 20 cm vertical is claimed for kinematic applications, anywhere on the globe, and at any time. This level of position accuracy is very promising for precise navigation of vehicles on land, sea vessels and aircraft, and for Geographic Information System (GIS) data collection, for instance with construction works and maintenance. A subset of some 40 reference stations of NASA’s Global GPS Network (GGN) allows for realtime streaming of data to a processing center, that determines and subsequently disseminates over the open Internet, in realtime, precise satellite orbits and clocks errors, as global differential corrections to the GPS broadcast ephemerides (as contained in the GPS navigation message). An introduction to IGDG can be found in Mullerschonetal. (2001a) and on IGDG (2004). Technical details are given in BarSever et al. (2001) and Mullerschonetal. (2001b).Internetbased users can simply download the lowband with correction data stream into a puter, where it will be bined with raw data from the user’s GPS receiver. The user’s GPS receiver must be a dual frequency engine and be of geodetic quality in order to extract maximum benefit from the accurate correct。 and the processing of the data, also for the global high precision IGStype (International GPS Service) of applications, is moving towards real time execution. As a result the traditional distinction between precise relative positioning with GPS and DGPS diminishes。周老師工作繁忙，但還是給了我很多的幫助，時(shí)刻關(guān)心我的成長(zhǎng)與進(jìn)步！還要感謝雷斌、楊曉明、袁天奇、王鐵生、張冰、黃桂平、馬開鋒、胡青峰、翟燕、孟俊貞等教研室和實(shí)驗(yàn)室的各位老師，在華水的幾年中他們?cè)趯W(xué)習(xí)和生活上都給了我很多的關(guān)心和照顧！值此論文完成之際，謹(jǐn)向他們表示我最衷心的感謝！感謝測(cè)繪2010011班的全體同學(xué)們，感謝他們這四年來的關(guān)心和幫助，是他們讓我對(duì)過去的歲月充滿了留戀。導(dǎo)師嚴(yán)謹(jǐn)?shù)闹螌W(xué)態(tài)度、淵博的學(xué)術(shù)知識(shí)、敏銳的洞察力、活躍的學(xué)術(shù)思想、孜孜不倦的工作作風(fēng)、寬厚的人格給予了我極大的啟迪和鼓勵(lì),必將對(duì)我的人生產(chǎn)生巨大的影響。2003．[14][D].鄭州：解放軍信息工程大學(xué)，2002.致謝本文是在周建業(yè)導(dǎo)師的悉心指導(dǎo)下完成的。GPS測(cè)量的未來也會(huì)更寬廣、更美好。本文研究的GPS工程控制網(wǎng)的布設(shè)是我們將在實(shí)際工作中遇到的問題，希望能為我們以后的工作提供幫助。展望隨著GPS技術(shù)在越來越多的領(lǐng)域中的應(yīng)用，在測(cè)量方面，GPS技術(shù)也是愈加成熟和廣泛，因此我們也應(yīng)該掌握這項(xiàng)技術(shù)技能，GPS在大地測(cè)量、工程測(cè)量、航空攝影測(cè)量、地球動(dòng)力學(xué)、海洋測(cè)繪、地籍測(cè)量、地形測(cè)量等方面已經(jīng)有大量的應(yīng)用。對(duì)GPS 工程網(wǎng)的布設(shè)，提出了三點(diǎn)建議，一是要注意到高精度點(diǎn)的分布；二是注意網(wǎng)的圖形結(jié)構(gòu)：三是當(dāng)進(jìn)行坐標(biāo)系統(tǒng)轉(zhuǎn)換時(shí)，注意重合點(diǎn)的分布和精度。同傳統(tǒng)測(cè)量相比，可極大地降低勞動(dòng)作業(yè)強(qiáng)度，減少工作量，提高作業(yè)效率。GPS 工程網(wǎng)布設(shè)，一般點(diǎn)位選擇靈活性較差，活動(dòng)范圍較小，觀測(cè)時(shí)間較短。結(jié)論GPS 作為一種全新、快捷、可靠的高精度測(cè)量手段，正對(duì)測(cè)量的傳統(tǒng)技術(shù)手段和方法產(chǎn)生重大變革。根據(jù)以上公式，可計(jì)算出方案一的可靠性為:=， =1，e=方案二的可靠性為:=，=1，e=顯然，方案二的可靠性比方案一略好。設(shè)GPS網(wǎng)中點(diǎn)的個(gè)數(shù)為n，用m臺(tái)接收機(jī)進(jìn)行觀測(cè)，則該網(wǎng)的最少觀測(cè)期數(shù)為 如重復(fù)設(shè)站率以R表示，則理論觀測(cè)期數(shù)為(5) 效率比較一個(gè)GPS網(wǎng)中，在測(cè)量點(diǎn)數(shù)、GPS接收機(jī)數(shù)和平均重復(fù)設(shè)站次數(shù)確定后，完成該測(cè)量所需的理論最少觀測(cè)期數(shù)就可以確定。利用相鄰點(diǎn)間弦長(zhǎng)精度計(jì)算公式:式中，GPS基線向量的弦長(zhǎng)中誤差(mm)，亦即等效距離誤差；a GPS接受機(jī)標(biāo)稱精度中的固定誤差(mm)；b GPS接受機(jī)標(biāo)稱精度中的比例誤差系數(shù)(ppm)；d GPS網(wǎng)中相鄰點(diǎn)間的距離(km)。(3) 成本比較成本取決于網(wǎng)點(diǎn)總數(shù)和重復(fù)設(shè)站率，設(shè)一臺(tái)接收機(jī)觀測(cè)一期的平均費(fèi)用為C，則總費(fèi)用為:f=C*S*m由于方案設(shè)站數(shù)多，數(shù)據(jù)處理平差費(fèi)多，方案一比方案二多花費(fèi)大約1萬元。方案一采用點(diǎn)連接和邊連接的混合連接形式，構(gòu)成異步環(huán)和復(fù)測(cè)邊，異步環(huán)具有良好的自檢能力，能有效地發(fā)現(xiàn)觀測(cè)成果的粗差，確保網(wǎng)的可靠性，復(fù)測(cè)邊連接時(shí)幾何強(qiáng)度較高。表42級(jí)別ABCDE閉合環(huán)或附和線路的邊數(shù)≤4≤5≤6≤8≤10圖42圖432)方案設(shè)計(jì)（圖中120為同步環(huán)）圖42 方案設(shè)計(jì)一圖43 方案設(shè)計(jì)二(1) 基本特征值比較根據(jù)R. A sany 提出的公式計(jì)算GPS網(wǎng)的主要特