Abstract. 1. Introduction. Brunel University 1 Anglia Ruskin University 2

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1 A ctcal assessment fo RINE Data fom OS NET fo GPS Accuacy Imovement M. AL Nabhan 1, S. AL Mas 2,W. Balachandan 1,. Hunat 2 m.alnabhan@bunel.ac.u, s.almas@angla.ac.u, w.balachandan@bunel.ac.u, zad.hunat@angla.ac.u Bunel Unvesty 1 Angla Rusn Unvesty 2 Uxbdge, Mddlesex Chelmsfod, Essex UB8 3PH CM1 1SQ U U Abstact In ode to move the GPS ostonng accuacy fo stand alone eceves, n a ost ocessng mode, an exemental wo was conducted based on GPS data obtaned fom Odnance Suvey netwo (OS NET). Data wee collected and stoed n a statonay locaton. Aftewads seveal dffeentally coecton methods wee efomed usng MATLAB. An accuacy aveage of 6 to 7 metes has been acheved. Results wee analyzed and dslayed usng GEO-Meda GIS softwae tool. ey Wods: OS NET, RINE, Geo Meda, DGPS, GPS 1. Intoducton Tunng off the Selectve Avalablty (SA), esults n ostonal accuacy movement usng a sngle eceve. Fo stand alone GPS eceves accuacy wee equal to 5m - 1m, 95% of the tme, comang to (1 m, 95%) wth SA, and the heght accuacy was geneally 15m to 2m 95% of the tme. Usng dffeental GPS (DGPS) coectons has also moved the accuacy hozontally and vetcally. DGPS coectons can be efomed n two modes; eal tme ocessng mode n whch the accuacy needs to be moved at the same tme the ostonng was eceved. The second mode s ost ocessng, n whch data must be collected fom two eceves, one wth a nown locaton (base staton) and the othe one s a ovng eceve. Accodngly, n ode to efom dffeental coecton thee s a need of base statons wee GPS eceves wth nown locatons ae laced [1]. OS NET ovdes a netwo of GPS eceves on nown onts that can be used as base statons fo suveyng wth GPS [2]. Odnance Suvey s the U natonal mang agency [3]; t s a efeence famewo fo all geosatal data n Geat Btan. One of thee concens s to suot the develoment and use of GPS system. Odnance Suvey has establshed a natonal netwo of nealy 1 GPS base statons, whch constantly tansmt GPS-obseved ostonng data fom aound U. Ths netwo s called OS Net. Ths netwo wos by ecevng aw GPS data at the base staton. Data s collected sent n eal tme va a dedcated communcaton channels to the Odnance Suvey. The data s qualty checed and then tansmtted wthn mllseconds to OS NET commecal atnes. Also, Odnance Suvey ovdes ths data fee n Receve Indeendent Exchange Fomat (RINE) to non-commecal uses afte two hous of the obsevaton n ode to be used fo GPS oston coecton n ost ocessng mode [3][4]. Ths ae ams to analyze the usablty of GPS data ovded by OS NET n movng the GPS oston obtaned fom a stand alone GPS eceve n a suveyng feld. The feld of analyss and measuements whee the exements too lace was at Angla Rusn Unvesty (ARU) camus locaton n U, n whch a GIS ma fom Odnance Suvey llustatng that locaton was used. The scale of the ma was 1:1, aste n whch the absolute accuacy of that ma was ±3.5m. Ths ae s oganzed as followng: secton 2 esents the bacgound behnd conductng ths wo, the thd secton exlans the hadwae and softwae comonents used to buld the exemental achtectue. Secton 4 demonstates the wo method and ocedue that has been used at the coecton staton; the esults conducted ae shown and analyzed n secton 5. Fnally, secton 6 concludes ths ae.

2 2. Related Wo A GPS accuacy suvey was efomed at the Golden Valley (Landange Sheet 161 SO3141 to SO3927) [5]. In ths suvey RINE data fom OS NET netwo wee used to asses and measue the accuacy of a low cost GPS eceve n that feld of suvey n a ost ocessng mode. The objectve was to be able to detemne sot locaton to an accuacy of 1m o bette n tems of ts Btsh Natonal Gd oston. Also, the object wll then be to use a dffeental GPS technque, oeatng ove a dstance of only a few lometes fom the local efeence staton at that secfc locaton. Smlaly, ths ae esents an exemental wo, measung the ostonng efomance of a low cost stand alone GPS eceve, n dffeent suvey locatons. Usng obsevaton GPS data obtaned fom Odnance Suvey netwo (OS NET) n a ost ocessng mode. The objectve was to move the ostonng accuacy obtaned fo futhe navgaton alcatons that wll be mlemented at the suvey locaton. Ths ost ocessng ocedue deends manly on thee elements; OS NET as a souce of RINE data, MATLAB to ocess and dffeentally coect the eceved GPS data and Geo Meda fo analyzng and lottng the esults and fndngs. Geo Meda Moble softwae was used, whch s an extenson of Geo Meda ofessonal. Ths GIS softwae tool s ovded by Integah Cooaton [6]. It ntegates Global Postonng System (GPS) and Geo Meda technologes. Ths softwae allows uses to access GPS data n eal tme to oent the ostons on a Geo Meda ma. Geo Meda allows uses to catue GPS data and to edt data moe easly and faste. It ovdes table to dgtzng and vecto tansfomaton fo data equng geomety tansfomaton. Automatc vecto beang and concdent geomety dgtzng allow uses to avod tadtonal data catue oblems. In ths wo MATLAB 7.4 was used n ode to ocess and dffeentally coect the eceved GPS data. MATLAB M-fles fom [7] have been used along wth othe MATLAB fles that have been wtten fo the uose of ths wo. 3. Exemental Achtectue and Man Comonents Dung the exements two man fles wee obtaned fom OS NET; obsevaton fle and navgaton fle, both fles ae n RINE fomats. Data collecton, ocessng, and fnally coecton wee efomed n a emote coecton staton whch was mlemented usng a lato equed wth a moble nteface cad to access the ntenet, n ode to acque the RINE fles fom OS NET seve dectly n the fled of study. Also, the lato was connected to a stand alone GPS eceve va Bluetooth connaton to ead the ove GPS data. Fgue 1 below llustates the exemental system man comonents and achtectue. Fgue 1: Exemental wo achtectue As shown n fgue 1, two man softwae tools wee used at the coecton staton Geo Meda ofessonal veson 6 and MATLAB 7.4. In addton, at the coecton staton an Intel Centno Fujstu Semens lato was used, ths lato was equed wth the followng: 1. HOLO BT-321 stand alone GPS eceve connected va Bluetooth. Ths eceve suots data ate of 96/384bs also t acques 32 satelltes. 2. Vodafone 3G data cad was used to establsh an ntenet connecton though Vodafone moble netwo. Ths cad utlzes Hgh Seed Downln Pacet Access (HSDPA) technology. The fled of suvey wee the measuement and analyss too lace was chosen at Angla Rusn Unvesty (ARU) camus, n whch the neaest OS NET staton that was used to obtan RINE fles was called SOHE, whch has an aveage baselne of 2lmotes fom the feld s locaton. GPS data collecton and measuements wee efomed all aound the unvesty camus n dffeent envonments

3 dung a numbe of days. Ths ae esents the measuement and testng esults at a selected fve dffeent laces at the unvesty camus aea. See fgue 2. The eason behnd ths selecton s to measue the effcency of the oosed system n a vety of locatons. Fgue 3: Coecton Sataton Wo Scheme Fgue 2: OS MAP showng the Feld of Exements The fve dffeent laces that have been chosen fo measuements ae sotted n ed colo and numbeed as shown n fgue 2. The exact oston of those fve locatons s nown fom the ovded GIS MAP nfomaton. The fst locaton s outsde the Fedc Chancello buldng man gate, the second one s at the unvesty cente. In sde the west buldng was the thd locaton to test the effcency of the system n an ndoo navgaton, the foth lace of GPS data collecton was at the unvesty ca a. Fnally, an oen sace locaton was chosen at the unvesty lay gound aea. These locatons wee denoted wth numbes 1, 2, 3, 4 and 5 esectvely. 4. Coecton Staton Wong Pocedue In ode to coect the ove s eceve oston and acheve an moved accuate oston at the suvey feld, seveal ocedues wee efomed at the coecton staton, see fgue 3. Afte ecevng the ovng GPS data fom the stand alone GPS eceve, all data wee stoed n a secal memoy buffe n the coecton staton. Then the oston of the ovng eceve was comuted nto Euoean Teestal Refeence System 1989 (ETRS89) GPS coodnates fomat and nto Catesan coodnates, Y, fomat [7][8]. The ETRS89 coodnates was used to select the neaest OS NET efeence staton. The Vodafone moble nteface cad was used to obtan the satellte data n RINE fomat fom the neaest OS NET staton. As mentoned eale, two man fles have been eceved fom OS NET the obsevaton and the navgaton fles, the heade secton n the obsevaton fle contans the exact oston of the efeence staton n Catesan coodnates, Y, fomat. RINE and GPS data fles wee conveted to MATLAB latfom fles n ode to be ocessed. Moeove, the ove eceve s oston was comuted and coected n Catesan coodnate fomat. Followng ae the dffeental coecton methods wee used wthn the coecton staton to coect the collected GPS data n ode to acheve the amed oston accuacy movement [9]: Fstly, the smlest coecton technque (oston coecton) was efomed by calculatng the OS NET staton s eceve oston ( s, Y s, s ) and then the dffeence between the calculated and nown oston (, Y, ) was comuted [8] [5]: = Y = Y S S Y.. (1) = S The comuted oston dffeences ae used to coect the eo n the ove eceve s oston, Y, ) dectly as the followng: (

4 ' = Y ' = Y ' = Y...(2) ( ', Y ', Whee ') eesents the coected ove eceve oston The second dffeental coecton method s seudo-ange coecton, n whch the exact oston of the efeence staton s nown, the dffeence between calculated seudo-ange and the nown one s consdeed to comute the amount of eo. These dffeences ae efeed to as seudo-ange coecton and denoted as P. The seudo-anges eos ae due to satellte obt eos, cloc eos and atmoshec delay. Theefoe, these dffeences ae used to calculate the eo n the ove eceve s seudo-anges wthn the same eoch of tme. Two dffeencng technques whee used; sngle and double dffeencng; fo sngle dffeencng the ove eceve s denoted as and the efeence eceve s denoted as j. Both eceves shae the same satellte. The dffeences n seudo-ange fo both eceves ae calculated as followng [9]: P = + c( dt dt ) + T + I + e...( 3) P j = c( dt dt ) T j I j e j j...( 4) Whee, P = Pseudo-ange measuement fom satellte to eceve = Geometcal ange between satellte and eceve c = Seed of lght dt = Satellte cloc offset T = Tooshee delay I = Ionoshee delay e = Eo n seudo-ange Then the dffeence n seudo-ange wll be P, ( ) T j = = e j β + cdt j + e j.( 5) Whee Y Y ( e T j ) = the unt s vecto wth decton fom satellte to eceve and β s the baselne whch equals to [, Y, ]. Afte lnea-zng the dffeence equaton (5) wll esult n: P + c( dt dt ) + T + I + e Y = j + j, j +, Y Y Y Y j, Y j + c( dt j dt ) T j I j e j... j, j (6) The efeence oston s nown and the onoshec, tooshec and mscellaneous eos ae emoved. Theefoe, the fnal equaton wll be: P = j + j, j + j, j + c( dt j dt ) + T j + j Y I Y j, Y j +...( 7) Afte sngle dffeencng, method atmoshec eos wll be elmnated. Stll thee wll be othe souces of eo such as the eceve and satellte cloc offsets. The cloc eos can be emoved by usng double dffeences. In double dffeence two satelltes ae used whch ae vewed by both efeence and ove GPS eceves. Detals concenng double dffeencng can be found n [9] [1]. All evously mentoned coecton methods wee mlemented usng MATLAB M-fles and wee used smultaneously n the coecton staton n ode to coect all collected GPS data. Fnally, the coected ove s eceve oston along wth the measued eceved oston and the exact nown ones wee lotted and comaed on a GIS MAP eesentng the feld of suvey usng Geo Meda GIS tool. 5. Results and Analyss GPS data collecton and measuement whee efomed fo seveal days and dung dffeent eods of day; monng, aftenoon and evenng. Afte obtanng all equed data, the ocessng and coecton ste as desced eale needs less than 1 mnute to be comleted. The eason why the testng wee efomed n a ost ocessng mode not n eal

5 tme, s that the RINE data needs one hou to be avalable though OS NET, theefoe all measuements should tae lace afte ecevng the RINE fles. Ths ae esents one samle of data measuement and ocessng conducted dung ea hous, between 2m to 5m, n a secfc wong day at Angla Rusn Unvesty camus aea. Fgues 4 though 6 eesents a comason between the values of the ovng eceve calculated, coected and exact oston coodnates at the selected fve laces. As mentoned befoe, that the ove eceve s ostons wll be conveted to Catesan coodnates (, Y, and ) n ode to be ocessed and coected. Fgue 4b below, shows that the values of the coected coodnate n the selected fve locatons wee becomng moe smla to the exact values of comang to measued coodnates, see fgue 4a; ths means that the coodnate values ae becomng moe accuate afte efomng the dffeental coecton though the oosed coecton achtectue. Fo all fgues fom 4 to 6 the axes eesent the locaton numbe (1, 2, 3, 4 and 5) whee measuement too lace. And the Y axes esent the coodnate value n metes V a l u e s ( M e t e ) Locaton Numbe Measued Values Exact Values Fgue 4a: Values Comason (Exact and Measued) V a lu e s ( M e t e s ) Locaton Numbe Coected Values Exact Values Fgue 4b: Values Comason (Exact and Coected) Smla to fgue 4b, fgue 5b esents an movement n the values of the Y coodnates afte the coecton ocess at all locatons. In the othe hand, fgue 5a shows that the dffeence between the obtaned Y coodnates and the exact Y coodnates changes deendng on the locaton of measuements. Fo examle thee was a lage dffeence value at locatons 2 and 3 the eason was because the GPS sgnal s affected by the unvesty buldngs and nfastuctue at these two onts. V alu es (M etees) Locaton Numbe Coected Y values Exact Y values Fgue 5a: Y values Comason (Exact and Measued)

6 Values ( M e t e s ) Locaton Numbe Coected Y values Exact Y values Accodngly, fgues 4 to 6 esent the actual movements n all ove eceve s coodnates, Y and. these movements has contbuted n the ecson of the ovng oston obtaned fom the HOLO GPS eceve n a ost ocessng mode. The coecton ocess efomance was vayng deendng on the selected locaton. Fgue 7, below llustates a vew of the aveage of the measued and coected ostons comang them wth the exact nown ostons at all selected locatons. Fgue 5b: Y values Comason (Exact and Coected) The movements n coodnate values ae also esented n fgue 6b below. Moeove, fgue 6a, llustates how the measued values of coodnates dffe fom the exact ones n dffeent locatons V a l u e s ( M ete ) Measued Values Exact Values Locaton Numbe Fgue 6a: values Comason (Exact and Measued) V a l u e s ( M ete s) Locaton Numbe Coected Values Exact values Fgue 6b: values Comason (Exact and Coected) Fgue 7: Geo Meda sceen shot showng aveage of (measued, coected and exact) ostons fo the selected locatons Fgue 7, s a sna shot taen fom Geo Meda softwae dung the coecton ocess, whee Chelmsfod cty ma has been used, to esent ARU camus locaton. The ed onts eesent the exact oston of each locaton, blue stas llustates the aveage of coected ostons at each locaton and the geen onts s the aveage of the measued ostons at each locaton. Fnally, afte comutng the aveage of movements n the ovng oston at all selected locatons, t was concluded that usng an OS NET RINE data wthn the exemental achtectue

7 oosed at the suveyed locaton esults n an accuacy movement equals to an aveage between 6 to 7 metes n a ost ocessng mode. 6. Concluson and Futue Wo Ths wo demonstates an exemental wo measung the ostonng efomance of a low cost stand alone GPS eceve n a secfed locaton. Afte data collecton and stong a set of coecton methods wee efomed on the ove eceve s oston usng RINE fles fom OS NET. Also the exements wee based on Geo meda softwae tool and on a GIS ma ovded fom Integah Cooaton. The conducted esults have oven the effcency of usng OS NET data n movng the ovng GPS oston accuacy obtaned fom stand alone eceve n dffeent locatons at the feld of suvey. Fo futue wo, dffeent navgaton alcatons such as blnd edestan alcaton usng a stand alone GPS eceve wll be mlemented n the same feld whee the ost ocessng coecton mode was efomed. [8]. Ponomayov I, Nno L, Olesy B, Donnadeu B, 2. Inceasng DGPS accuacy by use of alman flteng. The Intenatonal Socety fo Otcal Engneeng. [9]. Gou: 84, Insttute of Electonc Systems, Aalbog Unvesty, 24. Pefomance Analyss and Imlementaton of Conventonal and EGNOSbased DGPS setus. [1]. Faell J and Gvags T, 2. Dffeental GPS Refeence Staton Algothm Desgn and Analyss. IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, VOL. 8, NO. 3. Refeences [1]. Monteo L., Mooe T., Hll Ch., 25, what s the accuacy of DGPS? Jounal of Navgaton, Cambdge Unvesty, 58, Issue, [2]. Thess A., Davd C., Yuan C., 25, Global Postonng Systems: an analyss of alcatons, cuent develoment and futue mlementatons, Comute Standads & Intefaces, 27 (2), [3]. Acoyd N, Cuddace P, ''Geodetc OS Net Postonng accuacy at the heat of Geat Btan'', Odnance Suvey. [4]. Gutne W, 26. RINE: The Receve Indeendent Exchange Fomat Veson. Astonomcal Insttute, Unvesty of Bene [5]. Odnance Suvey, A gude to coodnate systems n Geat Btan. [6]. Integah Inc: (htt:// [7]. Boe, 23. The Easy Sute - Matlab code fo the GPS newcome, Techncal ae ublshed n: GPS Solutons, Volume 7, Numbe 1, 23, And MATLAB code ublshed n: (htt://