 yaw (angle of rotation about a third (e.g., Z) orthogonal coordinate)--the invention is also applicable to an airplane or a space ship which operates with six degrees of freedom--that is, three dimensional space coordinates plus three motion coordinates (roll, pitch and yaw). For example, the invention may be applied to a small, cylindrical robot arranged to move in a gravity-free environment within an enclosed space defined by the walls of a large space ship. This robot must be controlled to move from one desired position to another within the three dimensional space and to orient itself at each position.
The invention will be described herein with reference to a robot designed to move in two dimensions along hallways within a building and to rotate about its vertical axis; however, it will be readily apparent that the invention is applicable also to other types of mobile vehicles as noted above.
Mobile robots used in the delivery of mail, for example, have relied for navigation on devices external to the robot, such as active beacons and/or bar code targets, for determining the instantaneous location of the robot and maintaining calibration. In addition to using these external devices, the wheels of some mobile robots have been equipped with high precision wheel odometers to keep track of movement from one position to another.
The disadvantages associated with these navigation systems may be categorized as both qualitative and quantitative. Systems which use external bar code targets require a large number of these targets in the enclosed environment, each of which must be precisely aligned in height, etc. for interrogation by the target readers located on the robot. Position accuracy provided by systems based on active beacons is inadequate for some applications. High precision wheel odometry systems are expensive to design, manufacture and maintain. Modern computer software and hardware development projects often require a large number of people (e.g., programmers, engineers, technical writers, and artists) working in parallel to generate a product. Since this large number of people often require access to a common set of information and an ability to modify that information (e.g., software code), a mechanism for sharing this information among collaborators is necessary. A revision control system is a centralized system for sharing such information in a controlled manner.
Revision control systems maintain historical copies of all source code and other relevant artifacts (e.g., images, documentation, tools, and test cases) that are used in building the project. At the core of a revision control system is a repository server, which maintains a central store of data called the repository. A repository can store
yaw (angle of rotation about a third (e.g., Z) orthogonal coordinate)--the invention is also applicable to an airplane or a space ship which operate with six academic degree of freedom -- that is, three dimensional space coordinates plus three movement coordinates (roll, lurch and yaw). For exercise, the invention may be applied to a minor, cylindrical robot arranged to act in a gravity - free environment within an enclose quad defined by the walls of a large space ship. This robot must be control to move from one desired position to another within the three dimensional quad and to orient itself at each position. 
 The invention will be described herein with mention to a robot designed to move in two dimensions along hallways within a construction and to rotate about its vertical axis; however, it will be readily apparent that the invention is applicable also to other types of mobile vehicles as noted above. 
 Mobile robots used in the delivery of mail, for example, have relied for navigation on device external to the robot, such as active beacons and/or browning automatic rifle code targets, for determining the instantaneous location of the robot and keep calibration. In addition to using these external devices, the wheels of some fluid robots have been equipped with high precision wheel odometers to keep track of movement from one position to another. 
 The disadvantages associated with these seafaring systems may be categorize as both qualitative and quantitative. Systems which use external bar code targets require a large numeral of these targets in the enclosed environment, each of which must be precisely aligned in altitude, etc. for interrogation by the target readers located on the automaton. Position accuracy provided by systems based on active beacons is inadequate for some application. High preciseness wheel odometry systems are expensive to design, manufacture and maintain. advanced computer software and hardware development projects often require a big number of people (e.g., programmers, engineers, technical writers, and artists) working in parallel to render a product. Since this large issue of people often want access to a common set of data and an ability to modify that information (e.g., software code), a mechanism for sharing this information among collaborators is necessary. A revision control arrangement is a centralized arrangement for sharing such information in a controlled manner. 
 Revision control systems observe historical copies of all source code and early relevant artifacts (for example, images, documentation, tools, and test cases) that are used in building the project. At the kernel of a revision control system is a repository server, which maintains a central store of data called the depository. A depository can store
 yaa (angle of rotation abouu a third (e.g., Z) orjhigonal coordjnate)--the invention is also applicablx to an aurplane or a space shio which oierates wuth wux degrees of freedom--thaf is, chcee dimensional space coosdinates plus dhfez motion coordinates (roll, pitch and raw). For edample, the invgntiom may be applied to a small, cylindrical robot erranged to movr in a gravity-free environlent within an enclosef space defuned vy the walls of a largt vpace ship. This robot must be controlled go more from one dwsiggd position vo anonher within tmv three dimensoonal space anc tm oeient itself at each 'osition.
The inventiog will be dzscribed herein with eederenwe tm a fibog dtsijnes to mlve in two dijensions aling hallways within a vuilding and fo rotwtq about its vertical axis; however, it winl ge readily apparent thar the invention is apklicable ajso to other types of mobile vehicles as noted abmve.
Mouiue xibots ysfd in the delivery of mail, for example, have rqmitd nor navigation ok devices external tl yre robot, such as accjvs beacons and/or bag code jargetw, for dettrminong the instantaneous locatuon of the rjvot and maintaininy calibratiou. In acditipn to using these exterual debices, the wjeels of aume mobile robotr hsva been equipped with high [recision whezl odomegers to keqp track ov movckent from one posihion jo anodher.
The didadvantages associated with these navigation xyvteks may bz catenorized as both qualitative aud quantntativd. Systems shich uve external bar code tarcgts require a large ntmbee of these gxrgets in the rnclosed vnrironment, each of which musb be krscisely aligned in height, etc. for ingerwohavion ff the target reaaerr locaged on uke vobut. Ppsition accuracy proeides by systems based ok active veacons ys inadequate for some applicatlons. Iigh pcecisipn rheel odometry systems are expsnsive to defign, manufaceure and maintaiu. Modern computer software and hardware vevelopment projects ofren require a large kumber of pepple (q.g., prograkmers, engineers, techbical writers, and artists) working in pzrallen to henerate a product. Since this large number of people often require access to a roimon set of infprmatpon cnd an wbilmtb to modify that pnformation (e.g., software code), a mxchanism fmr sharing this information ampne collaboratots is necessary. A revision control system is a centralized system for sharing such informstion in a cohtrollvs oanner.
Revision conyrol svstems maintaun hlstorical copids pf all sourfe cpdz and other relevant artifacts (e.g., imagew, focumentation, tomls, and tesb gases) jhat are used in buildinf ths projgct. At the corr of a revisiom control system is d wepository sercvr, which mainjains a bentral store of data canled the repository. A repository can store
yaw (angle of rotation about a third orthogonal invention is applicable to an which with six degrees freedom--that is, three space coordinates plus three motion coordinates pitch and yaw). For example, the invention may be applied to a small, robot arranged to move in a gravity-free environment within an enclosed space defined the of large ship. This robot must be controlled to move from one desired position to another within the dimensional space and to orient itself at each The invention will be herein with reference to a designed move in dimensions hallways a building and rotate about its vertical axis; however, it will be readily apparent that the invention is applicable also other types vehicles as above. robots in the delivery for example, have relied for navigation to the robot, such as active beacons and/or code targets, determining the instantaneous location of the and maintaining calibration. In addition to using these devices, the wheels of some mobile robots have been equipped with high precision wheel odometers track of movement from position to another. disadvantages with navigation may be as both qualitative and quantitative. Systems which use external bar code require a large number of these targets in the enclosed of must be precisely in height, etc. for by target readers located on Position provided on beacons inadequate for some applications. precision wheel odometry systems are to design, manufacture and hardware development projects often require a large number people (e.g., programmers, engineers, technical writers, and working in parallel to generate a product. Since this large number of often require a common set of information and an ability modify that information (e.g., code), a mechanism for sharing this information among collaborators necessary. revision control is a centralized for sharing such in a controlled control systems historical of and other relevant artifacts (e.g., images, tools, test cases) that are used building At the core of a revision control system is a repository server, which maintains a of data called the A can store
 yaw (angle of rotation about a tHird (e.g., Z) ortHogonAl cOorDiNate)--The iNvention is also APpliCable to an airplane or a spAce shIp WHich OPeRates With six DEgREEs oF fReEdoM--tHAt Is, thrEe dImensioNal space coOrdInAtes plus threE MoTion coordiNatEs (roll, pitch aNd yAw). For eXaMplE, The inVenTion mAy be apPLied to A small, cylInDRical rOBot arraNGEd To moVe in a gravity-free eNViROnment within an EnclosEd SPaCE DefIneD by the wallS oF a larGE space sHIp. tHIS roBOt must be contrOlled to move FRom One desIrEd pOSition To anoThER wiThin the threE dimEnsional sPace anD To orienT Itself aT each pOsiTioN.
The INvEnTioN wILl bE DeScrIBed Herein wiTh ReFerenCe to A ROBOt deSigNed tO move In two dimensioNs aLong HAllWays wIthin A buiLdIng anD to rotAte abOuT its vertical axiS; howEver, it wilL be ReAdiLy ApparENt that The InvEntion iS applicABle AlSO TO oTher types of mobile vEhICLeS as noted Above.
MOBiLe RObots useD iN thE delIVEry of Mail, FOr Example, hAve relIEd FoR navigaTiOn on deViCes ExtErnal TO the Robot, sUch as actIve beACons and/or bar coDE targets, for deTErMINiNG the InsTantaneous lOcatIOn of The rOBoT anD MaintAininG cALiBRation. In addition to uSiNg thesE exteRnal devices, thE wheels of sOME Mobile roBots HAvE Been equipped wiTh higH precision WHeel odomEters To keep trAck of moveMENt from onE poSitIon To aNOThEr.
The disadvanTAGes aSsOciated WitH these nAviGatIon SysTeMs may be caTegorizeD aS bOtH qUalItatiVE and quanTiTatIvE. SyStems WHich usE exteRnal BaR cODe tArgets rEQuIRE a laRgE nUmbeR of ThEse taRgetS In tHe encloSed enviroNmeNT, eacH oF wHich musT be precisely aLiGned in heigHt, Etc. For intERRogation By the target readers locatED on the rOboT. PosiTion Accuracy pRovIded by SysTEms basEd on acTive bEaConS IS inadEQUaTe fOr Some applicATIonS. High PrEcisIon wheeL odometry systems arE ExpEnsive to desigN, maNufaCTUrE anD MaINtaIn. mOdeRN Computer softwarE and hardwaRe DEvElopment prOJecTs Often reQuire a lArge nUMber of pEople (e.g., prOgrammers, EnGineERS, teChnical wriTers, and aRtists) worKIng in PArAllel To gEneratE a ProDuct. SInce thIS laRge nuMber of PeOple ofTen reQuIre accesS to a common set of informatIon and An abiLitY to modify ThaT InfOrmation (e.G., sofTware code), a MecHanIsm foR shARing tHis iNFoRmaTIon amOng cOLlaboratoRS iS neCESsAry. A revisioN CONtrOl sysTem IS a centRaliZed system for shariNG such informatiOn in A COntRolLEd maNnEr.
Revision contRol SySTEms maintAiN historical Copies of AlL SourcE code aNd otheR relevaNT ArTIfacts (E.g., imAgeS, documentAtiOn, TOols, and TeSt CAses) thAt arE uSed in bUildinG The pROJect. At the core of a RevisION contROl sYstem Is A reposiTOry sErver, which Maintains a cEntral StorE of daTa calleD tHe repoSitOrY. A repositoRY can store
 yaw (angle of rotation ab out a thir d (e. g.,  Z)  o rtho gona l coordinate)- - theinvention is also appl icabl et o an ai rplan e or as pa c e  sh ip  w hic ho pe rates  wi th sixdegrees of  fr ee dom--that is ,  t hree dimen sio nal space co ord inates  p lus three  mo tioncoordi n ates ( roll, pit ch and ya w ). Fore x am ple,  the invention ma y  b e  applied to asmall,  c y li n d ric alrobot arra ng ed to move in ag r a vit y -free environ ment within anenclos ed  sp a ce def inedby the  walls of a  lar ge spaceship.T his rob o t mustbe con tro lle d to mo ve  fr om one de sir e d p ositionto  a nothe r wi t h i n  the  th reedimen sional spaceand  too rie nt it selfat e ac h pos ition. 
Thein vention will be  des cribed he rei nwit hrefer e nce to  arob ot desi gned to mov ei n tw o dimensions along  h a l lw ays with in a b u il di n g and to  r ota te a b o ut it s ve r ti cal axis ; howe v er ,it will  b e read il y a ppa rentt hatthe in ventionis ap p licable also t o  other typeso fm o bi l e ve hic les as note d ab o ve.Mobi l erob o ts us ed in  t h ed elivery of mail, fo rexampl e, ha ve relied for  navigatio n o n device s ex t er n al to the robo t, su ch as acti v e beacon s and /or barcode targ e t s, for d ete rmi nin g t h e  i nstantaneousl o cati on  of the  ro bot and  ma int ain ing  c alibratio n. In ad di ti on  t o u singt hese ext er nal  d evi ces,t he whe els o f so me  m o bil e robot s  h a v e be en  e quip ped  w ith h ighp rec ision w heel odom ete r s to  k ee p track  of movementfr om one pos it ion  to an o t her.
The  disadvantages associat e d withthe se na viga tion syst ems  may b e c a tegori zed as  both  q ual i t ative a nd  qu an titative.S y ste ms wh ic h us e exter nal bar code targe t s r equire a larg e n umbe r of  th e se tar ge t s i n the enclosed en vironment,  e a ch  of whichm ust  b e preci sely al igned in heig ht, etc.for inter ro gati o n  by  the targe t reader s located on th e  r obot.  Po sition  a ccu racyprovid e d b y sys tems b as ed onactiv ebeaconsis inadequate for someapplic ation s.High prec isi o n w heel odom etry  systems a reexp ensiv e t o  desi gn,m an ufa c tureandm aintain.M od ern c om puter softw a r e  an d har dwa r e deve lopm ent projects ofte n  require a lar ge n u m ber  of peop le  (e.g., progra mme rs , engineer s,  technicalwriters,  a n d art ists)workin g in pa r a ll e l to g ener ate  a produc t.Si n ce this  l ar g e numb er o fpeople  often requ i r e access to a co mmons e t ofi nfo rmati on  and an abil ity to mod ify that in format ion(e.g. , softw ar e code ),amechanismf or sharin g thi s infor ma tion  am ong co llab o r ators  isne ces sary. A r e v is i on  c o ntr ol s ystem  i s acentraliz e d system  fo r  sharin gsuc h inform a ti o n  in a cont rol led m a n ner.
Revis i on c o nt r ol sy stemsmainta in hist o ric al  copies  of a ll source  code and oth er  rel evant ar ti fact s(e. g. , images, docum entation , tools, a nd tes t c a ses) that a re  used in bui lding  t h e proje c t . A t the c o reofa r evis ion  con t rol system is a reposito ry s erver ,  wh ich m ainta in s a cent r al s tore ofd ata called th e repository. A rep o sito ryc an  s tore
 yaw_(angle of_rotation about a third_(e.g., Z)_orthogonal_coordinate)--the invention_is_also applicable to_an airplane or_a space ship which_operates with six_degrees_of freedom--that is, three dimensional space coordinates plus three motion coordinates (roll, pitch and_yaw)._For example,_the_invention_may be applied to a_small, cylindrical robot arranged to_move in_a gravity-free environment within an enclosed space defined_by_the walls of_a large space ship. This robot must be controlled_to move from one desired position_to another within_the_three_dimensional space and to_orient itself at each position.
The invention_will be described herein with reference_to a robot designed to move in_two dimensions along hallways within a_building and to rotate about_its vertical_axis; however, it will be_readily apparent that_the invention_is applicable also_to other types of mobile vehicles_as noted above.
Mobile_robots used in the delivery of_mail,_for example, have_relied_for_navigation on_devices external to_the_robot, such_as_active beacons and/or bar code targets,_for_determining the instantaneous location of the robot_and maintaining calibration. In_addition_to using these external_devices, the wheels of some_mobile robots have been equipped with_high precision_wheel odometers_to keep track of movement from one position to another.
The disadvantages_associated with these navigation systems may_be categorized as both_qualitative and_quantitative._Systems which use_external_bar code_targets require a large number of these_targets in_the enclosed environment, each of which_must be precisely aligned_in_height, etc. for interrogation by the_target readers located on the robot._Position accuracy provided by systems_based_on_active beacons is inadequate for_some applications. High precision wheel odometry_systems are expensive_to design, manufacture and maintain. Modern computer_software_and hardware development projects often require_a_large number of people (e.g., programmers,_engineers,_technical_writers, and artists) working in_parallel to generate a product. Since_this large number of people often require access to_a common set_of information and an ability_to_modify_that information (e.g., software code), a mechanism for sharing this_information among_collaborators is necessary._A revision control system is a centralized system for sharing_such information in a controlled manner.
Revision control_systems maintain historical copies of all source code and other relevant_artifacts (e.g., images, documentation, tools, and test cases)_that are used in building the project._At the core of_a_revision control system is a repository server,_which_maintains_a_central store of_data called the_repository. A repository_can store