6/29/2015 AutomatedDataCollection(GPSandGIS)Part3

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AutomatedDataCollection(GPSandGIS)Part3

PROJECT2B

TakingDataAlongaPath

Inthisprojectyouwillagainusethereceivertotakefixesandrecordthecoordinatesinthedatalogger.Thedifferencebetweenthisandthepreviousproject(2A)isthatyouwillmovethereceiverantennathroughspaceinordertorecorddatapointsalongatrack.ThiscapabilityallowsyoutogeneratethemoreinterestingfeaturesofaGIS:arcsandpolygons,ratherthansimplypoints.

Youmayselectoneofthreewaystomovetheantenna:byfoot,bicycle,orautomobile.Readthesectionsbelowtodecidehowyouwanttotakedata.(Intheeventthatyoucannottakemovingdata,severaldatafilesareprovidedontheCDROMthataccompaniesthistopic,soyoumayprocessthosefiles.Filesfoundthereincludethosetakenbyautomobile,bicycle,airplane,helicopter,sailplane,cruiseship,andsailboat.Ihavenodatapresentlyfromahotairballoonifyougeneratesome,pleasefeelfreetosenditin.)

Generatingaseriesofpointswhilemovingprovidessomechallenges.

Accuracy.Weindicatedthat180fixesatasinglelocationprovidedareasonableapproximationofthepositionoftheantenna.Incollectingdatawhilemoving,ofcourse,youwillcollectonlyonefixateachlocation,withtheconcomitantlossofaccuracy.

ConstellationVacillation.Whenyousetupthereceiveratasinglepoint,youcantrytooptimizetheviewofthesatellitesbystayingawayfromobstructions.Whilemoving,youhavelittleopportunitytopickthepointsatwhichthereceivercalculatesaposition.Astheantennamovesalongthepathtodifferentpositions,thereceiver,bysimplytryingtopickthebestsetoffoursatellitestocalculatepositions,maychoosedifferentconstellationsoffoursatellites,duetosignalobstructioncausedbytreecanopy,buildings,overpasses,ortunnels.Becauseofthevariouserrors,whicharedifferentfromsatellitetosatellite,apositionfixreportedbythereceiverusinganewconstellationmaybedifferentfromwhereitwouldhavebeenhadthepreviousconstellationbeenretained.Thus,thepositionfixesmaynotfollowacleanline,butmayjumpfromsidetosideofthetruepath.Asecondconsiderationintakingdataalongapathisthateachchangeinconstellationincreasestheamountofmemorynecessarytostoredata.

Multipath.Substantialerrorsmayoccurifagivenradiosignalfollowstwopathstothereceiverantenna.Thiscanhappenifapartofthesignalisbouncedoffanobject,suchasabuilding.Thearrivaloftwoormorepartsofthesignalatdifferenttimescanconfusethereceiverandproduceafalsereading.(Youmayhaveseentheresultsofmultipathonthescreenofatelevisionsetreceivingsignalsfromanantenna[notfromcable]itappearsas"ghosting"adoublingortriplingofanimage.)ManyGPSreceiversareprogrammedtodisregardthesecondsignal.Butaproblemcanoccurifthedirectsignalisblockedbuttherelatedbouncedsignalisseenbytheantennaandrecorded.

TakingDataonFoot

Whilewalking,youneedtobecarefultokeeptheantennahighenoughsothatnopartofyourbodyimpedesthesignal.WiththefirstversionoftheGeoExplorer,thismeansholdingithigh,welloutinfrontofyou,sothattheinternalantennacanhaveaclear"view"ofthesky.WiththeGeoExplorerIIwiththeexternalantenna,itisprobablyalsoagoodideanottowavetheantennaaroundanymorethanisabsolutelynecessary.Apole,withtheunitorantennaaffixedtoit,attachedtoabackpackisanicesolution.

Settheintervalbetweenloggedpointsbasedontime,notdistance,althoughyoumightthinkthattakingapointeverysomanyfeetormeterswouldseemlikeagoodidea.Theproblemisthatthereceiverwillrecordalmostallspuriouspointsthatoccur,becauseitissettorecordapointthatismorethan"d"

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6/29/2015 AutomatedDataCollection(GPSandGIS)Part3

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distanceawayfromthelastpoint.If"d"is,say,setto20feet,anderrorscreatesapoint25feetawayfromthelastpoint,thisspuriouspointwillberecorded.(Recallthatthereceiveractuallygeneratespointsatmorethanonepersecond.)If,instead,youarerecordingpoints,say,everyfourseconds,thenthereisabetterchancethataspuriouspointmaybeignored.Youmaycertainlytrythisbothways,butyouwillprobablygetaraggedpathwithmanyspikesinitbyusingdistanceastheloggingintervalwhilewalking.

Abriskwalkingspeedisaboutfivefeetpersecond,soyoucansetthetimeintervalaccordingly,dependingonthepointspacingyouwant.Forthisproject,ifyouarewalking,selectapath,preferablyclosed,ofamileortwo.

CollectingDatabyBicycle

Aneconomicalwaytocollectdataoversignificantdistancesalongalinearpathistouseabicycle.Butthereareanumberofpitfalls,inadditiontothegeneraldangersallbicyclistsface,mostlyfromautomobiles.Theprincipalproblemrelatestothelineofsightrequirement:unlesstheantennaispositionedfarawayfromyourbody,oraboveit,thereceiverwillconsistentlyloseitslockononesatelliteoranother.

Onesolutionnotrecommendedistoattachtheantennatothehighestpointonthe"you+bicycle"combination,butbicyclehelmetsareprettynerdylookingappliancesanywaywhenyouducttapeaGPSantennatothetopofittheeffectis,well,startlingtothepointthatneighborscomeoutwithcamerastocapturetheimage.Onesolutionisto"shootthemoon"asitwere,togiveupanypretenseofselfrespect,andclothetheantennainoneofthose"propellerbeanies."Someothersolutions:

haveaspecialbracketmadeforasurveyingpolewiththeantennaaffixed,

wearabackpackcontainingthereceiverwiththeantennaonapole

rideatandembike(abicyclebuiltfortwo),andattachtheantennatothesecondseat.Theeffectisstillprettyridiculousbutletsfaceit:youarentgoingtocollectGPSdataonabicyclewhilemaintainingasignificantlevelofdignityanyway.

CollectingDatabyAutomobile

Tocollectdatabyautomobileyoushouldideallyusetheremoteantenna,availablefortheGeoExplorerII,withamagneticmount.Placetheantennaontopofthecarandruntheantennaleadthroughawindow,preferablyinareardoor.Somesafetytips:6

Putathinpadofclothbetweenthemagneticmountandthecarrooftopreventscratchingthecarsfinish.

Ifyouwanttorollupthecarswindowbecarefulnottocrimptheantennawirebetweentheglassandtheframethisisespeciallyeasytodowithpowerwindows.

Donotopenthedoorthroughwhichtheantennaleadisthreaded.

Leaveenoughslackintheantennaleadoutsidethewindowsothatwhenyoudoaccidentallyopenthe"antennalead"dooryoudontdragtheantennaacrosstheroof.

Ifyouarenotusingaremoteantenna,placetheGeoExplorerasfarforwardonthedashboard,underthewindshield,asyoucan,sothatmetalofthecarsroofblockssignalsaslittleaspossible.

Oneadvantagetocollectingdatabycaristhatyoucanusethepowersupplyfromthevehicle.However,remembernottostartorstoptheenginewiththereceiverattachedtothecarspowersupply.Theproperorderofeventsis:

1.Startthecarengine,

2.Connecttheplugtothecarsauxiliarypower(cigarettelighter)receptacle,

3.Turnonthereceiver,

4.Whenyouareready,startrecordingdata.

Whenyouarethrough,undothestepsabove,inreverseorder.

Withautomobiledatacollection,youmayuseeithertimeordistanceasthelogginginterval.Whileerrorsmaystillbeaproblem,thedistanceyousetbetweenloggedpointsisgoingtobemuchgreaterwiththecarthanwhilewalking.Thus,thechanceofapointbeinggeneratedbyamultipatheventthatisgreaterthantheloggingintervalisreducedconsiderably.

Whileridingasapassengerintheauto(thedriverissupposedtokeepeyesontheroad)examinethenavigationscreenoccasionally.Youwillnoticethatitgivesthecarsspeedwithinamileperhourorso,andthedirectionaswell.(Youmaysettheunitsofdisplaysoastogetmilesperhourchangingunitswillnotaffectdatacollection,althoughpullingthereceiverbackfromitsplaceatthefrontofthedashmay.)

ActualDataCollection

{_}FillouttheinitialportionsoftheDataCollectionParameterSheet.

{_}Chooseamethodoftransportingtheantenna.

{_}Choosearouteperhapsaclosedloop.

{_}Checkandsettheparametersunder"Configuration~RoverOptions."

{_}Decideonarecordinginterval.

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{_}Startthedatarecordingprocess.

{_}Takeaminimumof200points.

{_}Stoprecordingdata.

{_}CompletetheDataCollectionParameterForm.

{_}Shutoffthereceiver.

PROJECT2C

BackInside

{_}Ifyouhavenotalreadydoneso,finishfillingoutthedatacollectionparametersheet(s)forthePROJECT2A(and2B)datacollectionsession(s).

{_}Comparethememoryusedandthenumberoffixescollected.

Howmanybytesdidtheaveragefixrequire?_.Ifthisismuchlargerthan25thenitmaybethattheunithadtorepeatedlychangeconstellations,andhencestoremoredata,tomaintainthesetoffoursatelliteswiththebestPDOP.Whileanyextendeddatacollectionsessionwillinvolveconstellationchangesafterall,eachsatelliteisonlyvisiblefromagivenpointoftheearthforafewhoursadayyouwillgetthebestdataifyouarecarefulnottoforceconstellationchangesbyobstructingthesignals.

WiththeGeo3youcangetsomeinformationaboutthefilesyoujusttookby:Fn&OPTION~File~OPTION~Fileinfo.Thenselectthefileyouwantinfomationaboutwiththeupanddownarrowkeys.Hereyouaretoldaboutthenumberofpositionsinfiles,butnottheirsize.IfyouwanttoknowthefilesizeyoucanusetheDeletemenuitemratherthanFileinfo.DonthitENTER.Youneedntdeletethefiletohavealookatit.UseCLOSE.

Atthispointyouhaverecordedspatialdata,butitisessentiallylockedawayinthedatalogger.Copyingitfromthedataloggerintoapersonalcomputer(PC)isthenextundertaking.Thisprocessissometimescalleduploadingdata.

{_}Thefirststepintransferringdataistomakeaphysicalconnectionbetweenthereceiver/dataloggerandthePC.Yourinstructorwillhavepavedthewayforthis.Probablyallyouwillhavetodoisconnectthedataloggertoacablewitharoundplug,theotherendofwhichisconnectedtothecomputer.7Itisveryimportantthatyouusecareinconnectingthecable.First,becarefulthatyoumerelyopentherubbergrommetassemblyonthebackoftheGeoExplorerdontpullthewholeassemblyoutoftheunit.Second,thecablewillfitintotheGeoExplorerpluginonlyonewayunlessyouforceit,inwhichcaseyoucanbendthedelicatepinsonthecableplug.Holdtheunitwithyourlefthand,outinfrontofyou,topsideup,withthebackfacingyou.Takethecableinyourrighthandand,withthecordgoingofftoyourright,maketheconnection.Theproperconfigurationiswiththeplugontheleftsideoftheunitandthecablestretchinghorizontallyacrossthebackoftheunit,totheright.

ConnectingtheGeo3toacomputercanbedoneinacoupleofways.ThesimplestistoconnectthecradlethatcamewiththeGeo3toboththecomputerandanACpowersupply.Probablythiswillhavebeendoneforyou.AllthatremainsistoputtheGeo3inthecradleandturniton.

ExecutethePathfinderOfficeSoftware

{_}StartthePathfinderOfficeSoftware:ImassumingthatyouhaveapassingfamiliaritywithWindows95,Windows98,WindowsNT,Windows2000,ortheirsuccessors.Ifnot,acrashcourseorsometutoringisinorder.YourinstructorwillhavegivenyousomedirectionsonhowtologontothecomputeryouwilluseandtoinvokePathfinderOffice.Followthosedirectionsnow.

{_}IfaSelectProjectwindowcameupwhenPathfinderOfficestarted,dismissit(byclickingthe"X"intheupperrightofthatwindow).TheresultsshouldlooksomethinglikeFigure210,perhapsmissingatoolbarortwowellfixthat.IfthePathfinderOfficewindowdoesnotoccupythefullscreen,doubleclickonitstitlebar.

"Project"isoneofthoseannoyingEnglishwordsthatsubsumetwodistinctlydifferentpronunciationsandmeaningsunderasinglespelling.8Asaverb,itcanmean,forexample,shinelightthroughfilmontoascreen,or"project"apieceoftheEarthssurfacetomakeamapthatis,makeageographic"projection."But"project,"asanoun,canmeanafocusofactivity,time,data,money,andsoon,soastoaccomplishsomegoal,asinto"launchaproject."

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Figure210.ThemainwindowofGPSPathfinderOffice.

InthecaseofPathfinderOffice,itmeansthelatter,although,sincethesubjectingeneralisgeographicdata,noonecouldcomplainhadyouguessedotherwise.Inanyevent,thefunctionofthe"Project"istoserveasaclosetforthefilesyouwillworkwith.

AProjectinPathfinderOfficehasseveralcomponents.FirstistheProjectName.Thisnamepointstoaprimaryfolder(preferablywiththesamename,butthatisnotrequired).Theprimaryfolderusuallycontainsdatafilesplusthreesubfolders,namedbackup,base,andexport.

{_}MakeanewProjectwithitsassociatedfolders:IntheFilemenuclickProjects.(FromnowonImayindicateasequenceofactionslikethisbyFile~Projects.)Click"New"intheSelectProjectwindow.

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Figure211.SettinguptheProjectanditsfolders.

A"ProjectFolders"windowwillappear.YouwillmakeaprojectwiththenameDATA_yis,where"yis"indicatesYourInitialS(incapitalletters,uptothree).Forexample:DATA_MK.

IfyouclickOKthewindowwilldisappearandtheSelectProjectwindowwillagainbecomeactive.

{__}ExaminetheSelectProjectwindow.ItshouldlookaboutlikeFigure212.Ifitdoes,okaythewindow.YouhavenowsetupPathfinderOfficesoitwillinstallyourfilesintheproperplaces.

Figure212.SelectingaProject.

Youhaveestablishedamainfolderforyourdata,andthreesubfoldersunderitforfunctionsthatwillbeexplainedlater.

{_}SelectOptions~Toolbarstomakesurethatchecksappearnexttoalltoolbarselections:Standard,Project,Mouse,andUtility.AlsomakesureacheckappearsnexttotheStatusBarmenuitem.

{_}CheckthattheProjectnameappearsontheProjecttoolbar.

Alsoonthistoolbarwillbetheamountofdiskspaceremainingontheassociateddiskdrive.Youshouldalsoseeafoldericon.Clickonit.Youwillseethecontentsofthefolderfortheproject.Itwillcontainthreefolders:backup,base,andexport.Dismisstheprojectfolder.

Totransferdatafromonedevicetoanother,theyhavetospeakinthesamedialect,asitwere.Thismeansthecommunicationparametersoneachdevicemustbesettothesamevalues.AcommonprotocoliscalledXMODEM.Acommonlyusedrateoftransferis9600bitspersecond(called"baud"10)whichresultsinabout1200bytes,orcharacterspersecond.11ParametersofParity,

CommPortA

1.ProtocolXMDM

2.Baud9600

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3.ParityNone

4.DataBits8

5.StopBits1

DataBits,andStopBitsrelatetotheconfigurationofbitsineachbytesent.

{_}SetthecommunicationparametersintheGeoExplorer:TurnontheGeoExplorerReceiver/Datalogger.Pick"Configuration~Communication~PortA."Thescreenwillprobablyappearasshownbelow.Ifnot,changetheparameterssoitdoes,unlessyourinstructorhasindicatedotherwise.

ProbablyyourPChasbeenconfiguredtoacceptdatainthisform.Thelocalconventionmaybedifferent,however.Ifthingsdontseemtobeworking,checkwithyourinstructor.

{__}Fromthemainmenuonthereceiver,select"7.DataTransfer."Thereceivershouldtellyouthat"CommisIdle."

TosetthecommunicationparametersontheGeo3,pickuptheunitfromthecradleandsimply:Fn&OPTION~Setup~Configurations~COMMS~Enter.ForDatatransferchoose"Supportmodule."SkipoverRCTMinputandNMEAoutput.SetthePortsettingstothoseshownabovefortheGeoExplorer.PressCLOSEacoupleoftimes.ReturntheGeo3tothecradle.

{__}PreparetoshipthefilesyoucollectedtothePC:InPathfinderOfficeselectUtilities,thenDataTransfer.12ShortlyaDataTransferwindowshouldappear,asinFigure213.

TheDevicefieldintheupperleftshouldconfirmthatyouareconnectedtoaGISdataloggertheportnameshouldbegiven.Ontherightsideofthewindowitwillindicatethetypeofdevice,e.g.GeoExplorerorGeo3.TheReceiveandSendbuttonsrefertotheprimarydirectionofdataflow.InthiscaseyouwantthePCtoreceivedata.

Figure213.ConnectiontoGeoExplorerpriortofiletransfer.

IfyoupresstheSettingsbuttonyoucan(1)saywhetheryoushouldbetoldifyouareabouttooverwriteafilealreadyonthecomputer(youshould),(2)whetheryouwantbackupcopiesofthefilesmadeonthePC(yes),and(3)whetherthefilesonyourGeoExplorerorGeo3shouldbedeletedaftertheyaretransferred(notagoodidea).

{__}Pressthe"Add"buttonandpickDataFile.An"Open"windowwillappearwithinityouwillseethelistofdatafilesthatresidewithinthedatalogger.PleaseseeFigure214.Moveyourmousecursoroverthebuttonsontheupperrightofthewindow.Presstheonethatsays"Details."Dependingonthedataloggeryouwillgetdifferentamountsofinformation.

{__}Select,byclickingwiththemouseonthefilename,oneofthefilesyouwanttoaddtotheDataTransferwindow.Ifyouwantmorethanonefileadded,holddowntheShiftkeyandclickontheotherfilenames.(Ifyouneedtostartoverinselectingfiles,clickinablankareaofthewindow.)Examinethe

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Destinationfieldtomakecertainthefilesaregoingwhereyouwantthemto.ClickOpen.The"Open"windowwilldisappearandthefilesyouselectedwillappearintheDataTransferwindow.

Figure214.TransferringfilesfromtheGeoExplorertothePC.

{__}Pickupthedatalogger[unlessitisaGeo3inthecradle]andholditsothatyoucanseebothitandthePCscreen.Pressthe"TransferAll"buttonandobserve.Thedataloggerwillindicatethatitissendingafile(thebargraphwilldecrease)thePCwillshowawindow(Receiving)indicatingthatafileisbeingreceived(itsbargraphwillincrease).Thismayallgobyprettyfastforsmallfiles.(Iftheprocessshouldstopbecauseofacommunicationerror,justpresstheTransferAllbuttonagain.Thetransfershouldproceedfromwhereithalted.)

{__}AfterthetransferstopsyoucanaskforMoreDetails.Read,thendismissthatwindow.ClickCloseontheTransferCompletedwindow.

{__}WhiletheDataTransferwindowisstillopen,repeattheprocess.Notethewarningyougetaboutoverwritingfiles.Youcandothisasmanytimesasyouwanttogetthefeelforhowtotransferdata.)Whenthrough,clickCloseontheDataTransferwindow.

{_}OntheProjectToolbarisafoldericonwithabluegreenlogo.

Whenyoupressit,upwillcomeawindowwiththemainprojectfolder:_:\GPS2GIS\DATA_yis.Notethatyourfiles,withtheextension"SSF"13meaningstandardstorageformatarelocatedinthatfolder.Thereisalsoa"Log"filegivingthedetailsofthetransfer.Notealsothethreesubdirectoriesorfoldersin_:\GPS2GIS\DATA_yis.Boththeexportandthebasefolderswillbeempty,butifyoudoubleclickthebackupfolderyouwillseethatitcontainsnotonlycopiesoftheSSFfilesyoujusttransferred,butalsoRAW(rawdata)filesthatconstituteintermediatestepsintheconstructionoftheSSFfiles.Youmayneverneedthesefiles,butthenagainyoumightlongafterthedatahavebeenclearedoutofthereceiver.Dismissthewindow.ExitPathfinderOffice.

{__}BeforeyoudisconnecttheGeoExplorerfromthePC,doExercise21.

ExerciseTransfertheAlmanac

Exercise2.1:ANAVSTARalmanacprovidesadescriptionofapproximatelywherethesatellitesareatanygivenmomentintime.CollectedbyandretainedintheGPSreceiver,thealmanactellsthereceiverwhichsatellitesitwillbeabletoseeduringadatacollectionsession.Thatis,thealmanachelpsintheinitialphasesofoutdoordatacollection.Sothereceiverautomaticallycollectsanalmanaceverytimeitisturnedon,ifitcan.Tocollectanalmanac,thereceiverneedstobepickingupthesignalfromatleastonesatelliteforabout15minutes.Almanacsareavailablefromthesatellites,allday,everyday,andusuallyhavevalidityforuptothreemonths.Ofcourse,ifanewsatelliteisputup,ortheexistingonesarerearrangedintheirorbits,thealmanacbecomeslessusefulimmediately.

ThealmanacmaybecopiedfromthereceivertothePCusingPathfinderOffice.HavinganalmanaconthePCisnotnecessaryinordertousethedatayouhavecollected,butlateryouwillseethatitisusefulforplanningadatacollectionsession.Forexample,whenusedwithaPathfinderOfficemodulecalledQuickPlan,itcantellyouhowmanysatellitesareavailableatanytimeduringtheday,andwhatDOPvaluesyoucanexpect.Furthermore,copyinganalmanactothePCisillustrativeofthecommunicationprocess,sowedoitforpractice.

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{__}WiththeGeoExplorerstillconnected,restartPathfinderOffice.Usingtheknowledgeyougainedfromtransferringfiles,setupPathfinderOfficetotransferthealmanactoyourPC.Youwillusethedatatype"Almanac."ThepathandOutputFilewillappearbydefaultas

C:\ProgramFiles\CommonFiles\TrimbIe\Almanacs\Almanac.ssf.14

ChangetheAlmanacnametoAlmanac_yisandstoreitin__:\GPS2GIS\DATA_yis.(YoucanstorethealmanaconthePCbyanynameandinanyplace.However,unlesstoldotherwise,QuickPlanwilllookforthelatestalmanacwiththename"Almanac"inthedefaultlocation.)WhenyoupressTransferAlltheGeoExplorerandPathfinderOfficewillbothcorrectlyclaimthatthealmanacisbeingtransferred.

{__}Whenthetransferisdone,closetheDataTransferwindowandexitPathfinderOffice.TurnofftheGeoExplorer,disconnectitfromthebatteryorotherpowersource,andcarefullydisconnecttheuploadcable.

Youhavecompleteduploadingyourdatafilesandthecurrentalmanac.(Youwereaskedtoputthealmanacinyourownfoldersinceothersmightwanttousethe"official"almanacin

C:\ProgramFiles\CommonFiles\Trimble\Almanacs\Almanac.ssf,whichmighthavebeencollectedatalatertime.)InthenexttopicyoulookatseveralsampledatafileswithPathfinderoffice,andthenatyourownfiles.

Nextpost:ExaminingGPSData(GPSandGIS)Part1

Previouspost:AutomatedDataCollection(GPSandGIS)Part2

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