GPS理論與應(yīng)用03

1、GPS理論與應(yīng)用（3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)）劉瑞華 教授中國(guó)民航大學(xué) 電子信息工程學(xué)院GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)授課內(nèi)容授課內(nèi)容1.GPS定位原理定位原理2.時(shí)鐘誤差問(wèn)題時(shí)鐘誤差問(wèn)題3.GPS的時(shí)間系統(tǒng)的時(shí)間系統(tǒng)4.GPS參考坐標(biāo)系參考坐標(biāo)系5.坐標(biāo)轉(zhuǎn)換坐標(biāo)轉(zhuǎn)換GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)1.GPS定位原理定位原理GPS is a distance (ranging) system. This means that the only thing that the user is tryin

2、g to do is determine how far they are from any given satellite. There is no inherent vector information, which implies azimuth and elevation, in the GPS signal. All that the GPS satellite does is shoot out a signal in all directions, although there is a preferential orientation toward the Earth.GPS理

3、論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)nGPS operates on the principle of trilateration(三邊測(cè)量三邊測(cè)量). The position of an unknown point is determined by measuring the lengths of the sides of a triangle between the unknown point and two or more known points.nThis is

4、 opposed to the more commonly understood triangulation(三角測(cè)量三角測(cè)量), where a position is determined by taking angular bearings from two points a known distance apart and computing the unknown points position from the resultant triangle.GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)nThe satellites do this by t

5、ransmitting a radio signal code that is unique to each satellite. Receivers on the ground passively receive each visible satellites radio signal and measures the time that it takes for the signal to travel to the receiver. GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)nDistance is then a simple matter of c

6、omputing D = V x T .nSince radio waves travel at the speed of light, the velocity is a given. Therefore, the only thing needed by the user to calculate distance from any given satellite is a measurement of the time it took for a radio signal to travel from the satellite to the receiver. GPS理論與應(yīng)用理論與應(yīng)

7、用 Introduction and Background(3)請(qǐng)注意，請(qǐng)注意，GPS是是單向測(cè)距單向測(cè)距系統(tǒng)，與聲納等的系統(tǒng)，與聲納等的雙雙向測(cè)距向測(cè)距系統(tǒng)不同系統(tǒng)不同GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)Single Range To A Single SV KnownnThe GPS Navstar satellite transmits a radio signal unique to each individual satellite. The signal is essentially omnidirectional, although th

8、ere is a preferential orientation toward the Earth since the satellites antennas aimed at the Earth. nIf we know that the range (distance) to a particular satellite is precisely 20,000 kilometers (for example), then the only place in the universe is somewhere on the surface of an imaginary sphere th

9、at has a radius of 20,000 kilometers.nWith only this amount of information there is no way to know where on the sphere we might be located.GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)Two Ranges To Two SVs KnownnWe can narrow down this positional ambiguity consi

10、derably by adding a range to a second satellite. nWe already know that were 20,000 kilometers away from the first satellite ( “A”). If we determine that were also 22,000 kilometers from another, second satellite ( “B”), we find that the only place in the universe which is that distance away from sat

11、ellite “B,” andis still 20,000 kilometers away from satellite “A,” is located somewhere on a circle where the two respective spheres intersect.nWhile this has narrowed down our position considerably, we still dont know where on the sphere-intersection-circle we are.GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Bac

12、kground(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)Three Ranges To Three SVs KnownnIf we add a third satellite with a known range of 21,000 kilometers, well almost be there. nNow, the only place in the universe is at the only two points where all three of the spheres happen to intersect.nWe now know w

13、here we are , at either one of two possible points. The receivers are smart enough to know the right one.nThree satellite ranges have given us our precise location in the universe. GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)2.時(shí)鐘誤差問(wèn)題時(shí)鐘誤差問(wèn)題nWhy, when three satel

14、lites can determine our three-dimensional position so precisely, do we need four satellites? nTo keep very accurate time, each satellite carries four atomic clocks on board, two rubidium and two cesium. These clocks are accurate to within billionths of a second per month. nEach receiver, on the othe

15、r hand, only carries “inexpensive” quartz clocks with much lower accuracy. GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)No Clock Timing Errornwe can look at the problem of clock timing error (clock bias error) as a two-dimensional problem by making several assum

16、ptions: First, that the clocks onboard the satellites are absolutely, exactly right on. Another assumption is that the receiver clock and the satellite clocks are in perfect synchronization. nIn the two-dimensional diagram we know that, we can only be at the two possible points where the two circles

17、 intersect. GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)Receiver Time One Second FastnThe fact is that the satellite and receiver clocks are never perfectly synchronized, and any error must be because of receiver clock(why?).nAssume that the receiver clock is f

18、ast by one second. This means that, it appears that the signal took one second longer than it really did(“seems” that much farther away than it really is ).nWith only two satellites, the receiver doesnt “see” a problem. Instead it calculates what it believes to be an accurate position based on the i

19、ncorrectly measured time/distance signals. GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)nAddition Of Another SV Time/RangenThe problem becomes apparent to the receiver when an additional satellite is included in the calculations. There is no place where the thre

20、e radii intersect.nAs soon as the receiver recognizes this, it knows that the problem is with its own internal clock and so it “skews” its clock setting slightly forward and backward until all three ranges intersect. GPS理論與應(yīng)用理論與應(yīng)用 Introduction and Background(3)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)

21、n接收機(jī)時(shí)鐘誤差對(duì)每次測(cè)量均是相同的，屬接收機(jī)時(shí)鐘誤差對(duì)每次測(cè)量均是相同的，屬于于公共時(shí)鐘偏差公共時(shí)鐘偏差。 這種偏差能夠通過(guò)求解方這種偏差能夠通過(guò)求解方程被消除或補(bǔ)償?shù)簦瘫幌蜓a(bǔ)償?shù)簦?測(cè)距圓便會(huì)交于一點(diǎn)。測(cè)距圓便會(huì)交于一點(diǎn)。n在實(shí)際應(yīng)用中，由于大氣效應(yīng)、各種干擾使在實(shí)際應(yīng)用中，由于大氣效應(yīng)、各種干擾使信號(hào)傳播受到影響，會(huì)導(dǎo)致測(cè)量值不準(zhǔn)確。信號(hào)傳播受到影響，會(huì)導(dǎo)致測(cè)量值不準(zhǔn)確。這些誤差稱為這些誤差稱為獨(dú)立測(cè)量誤差獨(dú)立測(cè)量誤差，很難消除。，很難消除。n在獨(dú)立測(cè)量誤差存在的情況下，三個(gè)測(cè)距圓在獨(dú)立測(cè)量誤差存在的情況下，三個(gè)測(cè)距圓不相交于一點(diǎn)，而是一個(gè)三角區(qū)域，即存在不相交于一點(diǎn)，而是一個(gè)三角

22、區(qū)域，即存在定位誤差定位誤差。 GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)GPS測(cè)距定位原理測(cè)距定位原理 利用利用4顆衛(wèi)星顆衛(wèi)星的測(cè)的測(cè)量值，估計(jì)接收量值，估計(jì)接收機(jī)機(jī)時(shí)鐘誤差時(shí)鐘誤差，并，并對(duì)星對(duì)星-站距離值進(jìn)站距離值進(jìn)行補(bǔ)償，通過(guò)求行補(bǔ)償，通過(guò)求解方程確定用戶解方程確定用戶接收機(jī)接收機(jī)位置位置。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)Levels Of GPS ServiceTwo levels of navigation and positioning are offered by the GPS: The Sta

23、ndard Positioning Service (SPS) and the Precise Positioning Service (PPS). nPPS is a highly accurate positioning, velocity and timing service that is designed primarily for the military and other authorized users.nSPS offers a base-line accuracy that is much lower than the PPS, but is available to a

24、ll users with even the most inexpensive receivers. There are various techniques available to increase the SPS accuracy.GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)nPublished specifications for the Precise Positioning Service are:17.8 meter horizontal accuracy27.7 me

25、ter vertical accuracy100 nanosecond time accuracynPublished specifications for the Standard Positioning Service are:100 meter horizontal accuracy156 meter vertical accuracy167 nanoseconds time accuracyGPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)3.GPS的時(shí)間系統(tǒng)的時(shí)間系統(tǒng)GPS disseminates a realization of coordinated

26、 universal time (UTC，世界協(xié)調(diào)時(shí)世界協(xié)調(diào)時(shí)) that provides the capability for time synchronization of users worldwide. Applications range from data time tagging to communications system packet switching synchronization.GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)1）UTC （世界協(xié)調(diào)時(shí)（世界協(xié)調(diào)時(shí)) nUTC is a composite time scale. Th

27、at is, UTC is comprised of inputs from a time scale derived from atomic clocks and information regarding the Earths rotation rate.nThe time scale based on atomic standards is called International Atomic Time (TAI). nTAI is a uniform time scale based on the atomic second, which is defined as the fund

28、amental unit of time in the International System of Units.GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)The other time scale used to form UTC is called Universal Time 1 (世界時(shí)，世界時(shí)，UT1). UT1 is a measure of the Earths rotation angle with respect to the Sun. It is one component of the Earth orientation paramet

29、ers that define the actual orientation of the ECEF coordinate system with respect to space and celestial bodies and is treated as a time scale in celestial navigationGPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)UT1 remains a nonuniform time scale due to variations in the Earths rotation. Also, UT1 drifts

30、with respect to atomic time. This is on the order of several milliseconds per day and can accumulate to 1 second in a 1-year period.The International Earth Rotation and Reference System Service (IERS) is responsible for definitively determining UT1. GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)UTC is a ti

31、me scale with these characteristics（TAI和和UT1）. The IERS determines when to add or subtract leap seconds to UTC such that the difference between UTC and UT1 does not exceed 0.9 second. Thus, UTC is synchronized with solar time at the level of approximately 1 second.GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、

32、坐標(biāo)系統(tǒng)2).GPS system timenGPS system time is referenced to UTC.nGPS system time is also “a paper time scale”; it is based on statistically processed readings from the atomic clocks in the satellites and at various ground control segment components. nGPS system time is a continuous time scale that is no

33、t adjusted for leap seconds. nGPS system time and UTC (USNO) were coincident at 0h January 6, 1980. GPS system time led UTC by 13 seconds(2006).GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)nThe GPS control segment is required to steer GPS system time within 1 s of UTC (modulo 1 second), but the difference

34、 is typically within 50 ns (modulo 1 second). nAn epoch in GPS system time is distinguished by the number of seconds that have elapsed since Saturday/Sunday midnight and the GPS week number.nGPS weeks are numbered sequentially and originate with week 0, which began at 0h January 6, 1980.GPS理論與應(yīng)用理論與應(yīng)

35、用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)3).接收機(jī)對(duì)接收機(jī)對(duì)UTC的計(jì)算的計(jì)算n在計(jì)算用戶在計(jì)算用戶PVT時(shí)確定其與時(shí)確定其與GPS系統(tǒng)時(shí)系統(tǒng)時(shí)的偏差的偏差tu，將這個(gè)偏差加到接收機(jī)時(shí)鐘，將這個(gè)偏差加到接收機(jī)時(shí)鐘的時(shí)間的時(shí)間trcv上便計(jì)算出上便計(jì)算出GPS系統(tǒng)時(shí)系統(tǒng)時(shí)。n在在GPS系統(tǒng)時(shí)與系統(tǒng)時(shí)與UTC之間的整數(shù)之間的整數(shù)閏秒值閏秒值tn由導(dǎo)航電文提供。由導(dǎo)航電文提供。n從而可以得到從而可以得到UTC時(shí)間：時(shí)間：tUTC=Trcv+tu+tn GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)4.GPS參考坐標(biāo)系參考坐標(biāo)系在在GPS應(yīng)用中，接收機(jī)雖

36、然處于地球附近，應(yīng)用中，接收機(jī)雖然處于地球附近，其位置隨同地球的自轉(zhuǎn)而運(yùn)動(dòng)，但其觀其位置隨同地球的自轉(zhuǎn)而運(yùn)動(dòng)，但其觀測(cè)目標(biāo)卻是受地球引力而繞地球運(yùn)動(dòng)的測(cè)目標(biāo)卻是受地球引力而繞地球運(yùn)動(dòng)的人造地球衛(wèi)星。人造地球衛(wèi)星。為了描述衛(wèi)星的運(yùn)動(dòng)情況，并正確處理衛(wèi)為了描述衛(wèi)星的運(yùn)動(dòng)情況，并正確處理衛(wèi)星的觀測(cè)數(shù)據(jù)，需要采用星的觀測(cè)數(shù)據(jù)，需要采用兩種類型的坐兩種類型的坐標(biāo)系標(biāo)系并實(shí)現(xiàn)坐標(biāo)系之間的相互轉(zhuǎn)換。并實(shí)現(xiàn)坐標(biāo)系之間的相互轉(zhuǎn)換。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)一類是在一類是在空間固定空間固定的坐標(biāo)系，該坐標(biāo)系與的坐標(biāo)系，該坐標(biāo)系與地球自轉(zhuǎn)無(wú)關(guān)，對(duì)描述地球自轉(zhuǎn)無(wú)關(guān)，

37、對(duì)描述衛(wèi)星衛(wèi)星的運(yùn)行位置的運(yùn)行位置和狀態(tài)極其方便。和狀態(tài)極其方便。另一類是另一類是與地球體相固聯(lián)與地球體相固聯(lián)的坐標(biāo)系統(tǒng)，該的坐標(biāo)系統(tǒng)，該系統(tǒng)對(duì)表達(dá)系統(tǒng)對(duì)表達(dá)地面地面觀測(cè)站的位置和處理觀測(cè)站的位置和處理GPS觀測(cè)數(shù)據(jù)尤為方便。觀測(cè)數(shù)據(jù)尤為方便?？梢酝ㄟ^(guò)坐標(biāo)可以通過(guò)坐標(biāo)平移平移、旋轉(zhuǎn)旋轉(zhuǎn)和和尺度變換尺度變換，將，將點(diǎn)的位置由一個(gè)坐標(biāo)系變換到另一個(gè)坐點(diǎn)的位置由一個(gè)坐標(biāo)系變換到另一個(gè)坐標(biāo)系。標(biāo)系。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)坐標(biāo)系統(tǒng)是由坐標(biāo)坐標(biāo)系統(tǒng)是由坐標(biāo)原點(diǎn)位置原點(diǎn)位置、坐標(biāo)軸指向坐標(biāo)軸指向和和尺尺度度所定義的。所定義的。在在GPS定位中，坐標(biāo)系原

38、點(diǎn)一般取定位中，坐標(biāo)系原點(diǎn)一般取地球質(zhì)心地球質(zhì)心，而坐標(biāo)軸的指向具有一定的選擇性，為了使而坐標(biāo)軸的指向具有一定的選擇性，為了使用上的方便，國(guó)際上都通過(guò)協(xié)議來(lái)確定某些用上的方便，國(guó)際上都通過(guò)協(xié)議來(lái)確定某些全球性坐標(biāo)系統(tǒng)的坐標(biāo)軸指向，這種共同確全球性坐標(biāo)系統(tǒng)的坐標(biāo)軸指向，這種共同確認(rèn)的坐標(biāo)系稱為認(rèn)的坐標(biāo)系稱為協(xié)議坐標(biāo)系協(xié)議坐標(biāo)系。協(xié)議天球坐標(biāo)系和協(xié)議地球坐標(biāo)系是兩種常見(jiàn)協(xié)議天球坐標(biāo)系和協(xié)議地球坐標(biāo)系是兩種常見(jiàn)的協(xié)議坐標(biāo)系。的協(xié)議坐標(biāo)系。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)1).協(xié)議天球坐標(biāo)系協(xié)議天球坐標(biāo)系 天球天球：以地球質(zhì)心為球心，半徑為無(wú)限大的假：以地

39、球質(zhì)心為球心，半徑為無(wú)限大的假想球體。想球體。 天極天極：地球自轉(zhuǎn)軸與天球面的交點(diǎn)，有北天極：地球自轉(zhuǎn)軸與天球面的交點(diǎn)，有北天極和南天極這兩個(gè)天極。和南天極這兩個(gè)天極。 天球赤道面天球赤道面：通過(guò)地球質(zhì)心與天軸垂直的平面。：通過(guò)地球質(zhì)心與天軸垂直的平面。 黃道黃道：地球公轉(zhuǎn)軌道面與天球相交的大圓。即：地球公轉(zhuǎn)軌道面與天球相交的大圓。即地球上的觀測(cè)者所見(jiàn)到的太陽(yáng)在天球上的運(yùn)動(dòng)地球上的觀測(cè)者所見(jiàn)到的太陽(yáng)在天球上的運(yùn)動(dòng)軌跡。黃道面與赤道面的夾角稱為黃赤交角，軌跡。黃道面與赤道面的夾角稱為黃赤交角，約約23.50。 春分點(diǎn)春分點(diǎn)：當(dāng)太陽(yáng)在黃道上從天球南半球向北半當(dāng)太陽(yáng)在黃道上從天球南半球向北半球運(yùn)行時(shí)

40、，黃道與天球赤道的交點(diǎn)球運(yùn)行時(shí)，黃道與天球赤道的交點(diǎn)。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng) 在天文學(xué)和衛(wèi)在天文學(xué)和衛(wèi)星大地測(cè)量學(xué)星大地測(cè)量學(xué)中，中，春分點(diǎn)和春分點(diǎn)和天球赤道面是天球赤道面是建立參考系的建立參考系的重要基準(zhǔn)點(diǎn)和重要基準(zhǔn)點(diǎn)和基準(zhǔn)面基準(zhǔn)面。天球示意圖天球示意圖GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)天球坐標(biāo)系天球坐標(biāo)系 在天球坐標(biāo)系中，任一天體的位置可用天球空在天球坐標(biāo)系中，任一天體的位置可用天球空間直角坐標(biāo)系和天球球面坐標(biāo)系來(lái)描述。間直角坐標(biāo)系和天球球面坐標(biāo)系來(lái)描述。天球空間直角坐標(biāo)系天球空間直角坐標(biāo)系

41、的定義：原點(diǎn)位于地球的的定義：原點(diǎn)位于地球的質(zhì)心，質(zhì)心，z軸指向天球的北極軸指向天球的北極Pn，x軸指向春分軸指向春分點(diǎn)點(diǎn) ，y軸與軸與x、z軸構(gòu)成右手坐標(biāo)系。軸構(gòu)成右手坐標(biāo)系。天球球面坐標(biāo)系天球球面坐標(biāo)系的定義：原點(diǎn)位于地球的質(zhì)心，的定義：原點(diǎn)位于地球的質(zhì)心，赤經(jīng)赤經(jīng) 為含天軸和春分點(diǎn)的天球子午面與經(jīng)過(guò)為含天軸和春分點(diǎn)的天球子午面與經(jīng)過(guò)天體天體s的天球子午面之間的交角，赤緯的天球子午面之間的交角，赤緯 為原為原點(diǎn)至天體的連線與天球赤道面的夾角，向徑點(diǎn)至天體的連線與天球赤道面的夾角，向徑r為原點(diǎn)至天體的距離。為原點(diǎn)至天體的距離。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)

42、間、坐標(biāo)系統(tǒng) 天球空間天球空間直角坐標(biāo)直角坐標(biāo)系與天球系與天球球面坐標(biāo)球面坐標(biāo)系的系的定義定義GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)2).地心慣性（地心慣性（ECI）坐標(biāo)系）坐標(biāo)系For the purposes of measuring and determining the orbits of the GPS satellites, it is convenient to use an Earth-centered inertial (ECI) coordinate system. A GPS satellite obeys Newtons laws

43、 of motion and gravitation in an ECI coordinate system.定義定義：原點(diǎn)：原點(diǎn)-地球質(zhì)心；地球質(zhì)心；X軸軸-由地心指向春分由地心指向春分點(diǎn)；點(diǎn)；Z軸軸-由地心指向北極；由地心指向北極；Y軸：軸：XY平面與平面與赤道面重合，構(gòu)成右手坐標(biāo)系。赤道面重合，構(gòu)成右手坐標(biāo)系。GPS理論與應(yīng)用理論與應(yīng)用3.工作原理與時(shí)間、坐標(biāo)系統(tǒng)工作原理與時(shí)間、坐標(biāo)系統(tǒng)3).地心地球固連（地心地球固連（ECEF）坐標(biāo)系）坐標(biāo)系For the purpose of computing the position of a GPS receiver, it is more convenient to use a coordinate system that rotates with the Earth, known as an Earth-centered Earth-fixed (ECEF) system. In ECEF system, it is easier to compute the latitude, longitude, and height p