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6/29/2015 ExaminingGPSData(GPSandGIS)Part3
http://whatwhenhow.com/globalpositioningsystemandgis/examininggpsdatagpsandgispart3/ 1/6
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ExaminingGPSData(GPSandGIS)Part3
ManipulatingFiles
{__}Selectthethreefilesleadingawayfromthevolcanotoprepareforcombiningthemintoasinglefile:Underthemenu"Utilities"select"Combine."Intheresulting"CombineDataFiles"window,press"Browse"tobringupalistoffilesinthefolder.Notethatasyouhighlightafilenameby(single)clickingonit,yougetinformationonthatfile.Pickthethreefilesfromthelist,usingthesameapproachasyoudidwhenyouopenedthemoriginally.(Thelittleinputlineunder"FileName"maynotbelargeenoughtocontainallthenames,butiftheyarehighlightedinthelisttheyaresettobecombined.)Click"Open"tosendthefilenamestothe"CombineDataFiles"window.
{_}Combinethethreefilesintoasinglefilenamed"AWAY.SSF":Press"OutputFile."Navigateto_:\GPS2GIS\HAWAII,sothatthe"Savein"directoryfieldsays"Hawaii."Under"FileName"type"AWAY.SSF."PresstheSavebutton.(Youmayhavenoticedbythistimethatfilenamesarenotcasesensitive.Iusecapshereinthetextforbettercontrastwiththeotherwordsinthesentence.)
Figure34.Combiningmultipledatafiles.
BackintheCombineDataFileswindow,makecertainthatthe"Sort"sectionindicatesthatthefilesshouldbecombinedchronologically(intimeorder)and,
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6/29/2015 ExaminingGPSData(GPSandGIS)Part3
http://whatwhenhow.com/globalpositioningsystemandgis/examininggpsdatagpsandgispart3/ 2/6
aftercheckingalltheparameters,okaythe"CombineDataFiles"window.Reviewtheinformation(itshouldappearasinFigure34)andthenclickOK.IfyouaretoldthefileAWAY.SSFalreadyexists,electtooverwriteit.
{_}Returnto"File~Open"andopenthetwofilesVOLCANO.SSFandAWAY.SSF.Youshouldseethetriparoundthevolcanoandthereturntrip.OpenthePositionPropertieswindowandselectpointsalongeachroutenotingthefilenames.
Thetriptothevolcanowasalongthesametwolaneroadasthetripawayfromit.The"to"tripwasrecordedasB021520B.SSF.12
{__}OpenVOLCANO.SSF,AWAY.SSF,andB021520B.SSF.NotethatitishardtodistinguishbetweenAWAY.SSFandB021520B.SSF.
PathfinderOfficeallowsyoutorepresentdifferentfeaturestypeswithdifferentsymbols.Butitdoesntallowyoutorepresentdifferentfilesofthesamefeaturetypewithdifferentsymbols.Sinceallthreeofthedisplayedfilesareoffeaturetype"NotInFeature,"theyarealldisplayedinthesameway.IwouldlikeyoutoseetheB021520BfileandtheAWAYfilewithdifferentsymbolssothatyoucancontrastthem.Iproposearuse.Usually,differentfeaturetypesaregeneratedwithadatadictionary,ofwhichmorelater.ButthesoftwareallowsthreefeaturetypestobemadefromNotInFeaturedata.TheyarePoint_generic,Line_generic,andArea_generic.TheruseisthatwearegoingtoconverttheB021520BfileintoaLine_genericfilesowecandisplayitdifferently.WewillusetheGroupingUtility,normallyusedtogroupanumberoffilestogether,toconverttheB021520Bfile.
{_}Usethe"Grouping"utilitytotaketheNotInFeaturedataofB021520B.SSFandconvertitintothe"Line_Generic"featuretype:Under"Utilities"select"Grouping."(OryoucouldpresstheGroupingiconontheverticalUtilitybar.)OntheGroupingwindowintheSelectedFilessection,click"Browse,"navigatetoandselecttheB021520Bfile.ClickOpen.ForanOutputFile,navigatetothe_:\GPS2GIS\HAWAIIdirectory.
Rejectthesuggestedname"grouped.xxx"anduseTOWARDS.SSFinstead.Thegroupingmethodshouldbe"Onegroupperinputfile"andthefeaturetypeyoucreateshouldbe"Lines."Readthe"Tip"atthebottomofthepage,thenclickOKandtheutilitywillfinish.(Ifitcomplainsthatthefilealreadyexists,selecttheoptionthatletsyouoverwriteit.)PleaseseeFigure35.
{__}OpentheSSFfilesVOLCANO,AWAY,andTOWARDS.UnderView~Layers~Featureschangethe"NotInFeature"linestyletothethinnestgreenline.Changethe"Line_generic"symboltomoderatelythinunconnectedblackdots.Checktheboxessothatallwillbeshownonthemap.Oncetheyaredisplayed,thedotsfromTOWARDSwilloverlaymuchofthelinefromAWAY.Youcanformanideaofthedegreetowhichthesetracksarecongruent.
{_}MakesuretheunitsareMeters.Pickasouthernpartoftheroadtothevolcanoandzoomuponitalot(sothatmaybeonlyfiveorsodotsofTOWARDS.SSFshow).Whatistheapproximatedistancebetweenthedots?__________________
Figure35.Usinggroupingtochangefeaturetype.
6/29/2015 ExaminingGPSData(GPSandGIS)Part3
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{_}Zoomwayuponasingledot(pickonethatstandsawayfromthelineabit)sothatonlyitappearsonthemapwiththegreenline.WhatisthedistancebetweentheTOWARDS.SSFdotandtheAWAY.SSFline?_.Sincethewidthofthistwolaneroadisonlyaboutsixmeters,towhatdoyouattributethedifferenceyoumeasured?_ZoomExtents.
{_}YouveseenthewindowthatwillallowyoutokeepNotInFeaturedatafrombeingdisplayed.Findthatwindowandturnoffthevolcanotrackandthedriveawayfromit.The"BigIsland"hastwomajorcities.UsingamaporatlasortheInternet,determinefromwhichcitytheGPStrackTOWARDthevolcanooriginated.
{_}Finally,fromtheDatamenu,turnoffthePositionPropertieswindow.FromtheViewmenuturnofftheMap.
PROJECT3BRooftop
Inthisexerciseyouwillfindasinglepointin3Dspacethatapproximatesthelocationofanantennathatcollecteddataatafixedlocation.WelookfirstatafileofpointstakenbyaGPSreceiverwhoseantennawasstationaryoveraperiodoftimebeforeselectiveavailability(SA)wasturnedoff.TheseGPSreadingsweretakenfromthetopofaroofofahouseinaKentuckycity.Theideahereisthatwearetryingtolocateasinglegeographicpointasaccuratelyaspossible.Todothatwetakelotsoffixesandaveragethem.Thedatatakenwere"NotInFeature"databutwewillconvertthemtoasinglePointgenericdatumsowecanplotthefixes.ThenwetakealookatthreefilestakenatthesameplaceafterSAwasturnedoff.
{_}StartthePathfinderOfficesoftwareifitisnotalreadyrunning.
{_}MakeanewprojectnamedROOF_yis,where"yis"representsyourinitials.Besurethe"Project"referencesthedirectory__:\GPS2GIS\ROOFTOP.(Youwillbetoldthatthefolderalreadyexistsandaskedifyouwanttocontinueanyway.Youdo.)
{__}PreparetoopenthefileB022721A.SSFwhichyouwillfindinthedirectory__:\GPS2GIS\ROOFTOP.(Therightdirectory,withtherightfilename,shouldcomeupsinceyouractiveprojectisROOF_yisanditreferencestheROOFTOPdirectory.)Writethedayandmonthofthefile,asindicatedbythefilename,(_______)andthenopenitbutdontmapityet.
{__}ChangethecoordinatesystemtoUniversalTransverseMercator.SettheUTMzoneto16North.13ChangethedatumtotheNorthAmericanDatumof1927(NAD1927)(ConusmeansContinentalUS,CoterminousUS,thelower48states).Makecertaintheunitsaremeters.Setthetimezonecorrectlybasedonthefiledate.(ThecityisintheEasterntimezone.DaylightsavingstimerunsfromthefirstSundayinApriltothelastSundayofOctober.)
Figure36.Thetimespanoftherooftopfile.
{_}Under"View"select"TimeLine."Notetheappearanceofawindowshowingthestartandendtimesofdatacollection.Stretchitouthorizontally.ZoomtoExtents.(SeeFigure36.)Usethe"F1"keytogetcontextsensitivehelp.Readaboutthetimeline.Itwillbealotmoreinterestinglaterwhenwecollectattributedatawiththepositiondata.Examinealsothetableofcontentsofthehelpwindow.Whendone,dismissthehelpwindow.
{__}Whatwastheweatherliketheafternoonthedataweretaken?
{_}Select"Map"under"View."Youwillgetamapboxbutmaynotgetamap.Whynot?__________.Ifyoudontknow,theresahintinthisfootnotethoughyoucanprobablyfigurethisoutwithoutit.
{_}UnderView~Layers~Features,makesurethereisacheckmarksoPathfinderOfficewillshowNotInFeaturedatauseathinredlinewiththepointsjoined.ApplyZoomExtentstoboththemap(aftermakingitactive)andtheTimeLine(aftermakingitactive).
{__}Nowthatyoucanseeallthefixesthathavebeentaken,whatistheapproximatedistancebetweenthefixesfarthestapart?
{__}Forthemostpart,thetimeadjacentpointsyouseehereareclosetogetherintermsoflocation.TheGPStrackmeandersaroundthespacesortofcasually.Butnotethattowardthemiddleofthewindowsomejaggedspikesappear.Zoomuponthem.Withtheselectiontool,selectapointattheendofoneofthespikes.
{__}OpenthePositionPropertieswindowandselecttheDOPstab.Usethemousedrivenselectiontoolandthe>andand
6/29/2015 ExaminingGPSData(GPSandGIS)Part3
http://whatwhenhow.com/globalpositioningsystemandgis/examininggpsdatagpsandgispart3/ 4/6
memoryforrecordingthesatellitesinthenewconstellation.
{__}InPositionPropertiesclicktheSummarytab.Howmanypointsarethere?_________.Overwhatperiodoftimewasthefilecollected?(ClickFirstandLastalsoseetheTimeLine.)______________.WhatUTMZonecontainsthepoints?(CheckunderOptions,CoordinateSystem,presumingyousetitcorrectly.)__________.Whatcitycontainsthepoints?(Youmighthavetochangethecoordinatesystemtolatitudeandlongitudeandthengotoanatlasoraworldwidewebsite__________.)
Makeasinglepointthatrepresentsthefixes
WepreviouslyusedtheGroupingutilitytoconvertraw(positionsonly)GPSfixesintoaLine_genericfeaturerecallconvertingtheGPStracktowardthevolcanoinProject3A.ThistimewewillconvertasetofrawGPSfixesintoasinglepoint,offeaturetypePoint_generic.Ingeneral,Groupingallowsyoutouseoneormoreinputfilestocreateoutputfile(s)withfeatures.Wewilluseittoaverageasetofpointsinafile(thatis,makeasinglepointsuchthatthexcoordinateisthearithmeticmeanofallthexvalues,samefory,sameforaltitude[z]).ThefeaturetypePointgenericallowsustopickasymbolformappingthepoint.
{_}MakeanSSFfilethatconsistsofasinglepointthatrepresentsthecentroid(thethreeaverages)ofallthepointsinthefile:UnderUtilitiesselectGrouping(orpickitofftheUtilitiesToolbar).Fortheinputwewilluseonlythe900pointfileB022721A.SSFintheGPS2GIS\ROOFTOPdirectory.PuttheoutputintotheROOF_yisProjectdirectory__:\GPS2GIS\ROOFTOP.Thesoftwareproposesthatyoucalltheoutputfile"GROUPED"butyoushouldmakeitinstead"ROOFMEAN.SSF."UnderCreateFeatureType,selectPoints.ClickOK.TheGroupingutilitywillcreateaPoint_genericfilenamedROOFMEAN.SSFconsistingofasinglepoint.ThefileB022721A.SSFwillremainasa900pointNotInFeaturefile.
{_}DisplayROOFMEAN.SSFinred,usingaroundsymbol:OpenbothB022721A.SSFandROOFMEAN.SSF.SelectPoint_genericfromtheView~Layers~Featureswindow,thenselecttheSymbolyouwant.AlsosetthingsupsoyouwilldisplayB022721A.SSFwithathin,lightcyanline.Drawthemapwithbothfilesrepresented.
{__}UsethepointertoselectthepointthatrepresentsROOFMEAN.SSF.(Whenitisselectedaboxwillappeararoundit.)SincetheROOFMEAN.SSFfileconsistsofasinglepoint,whatyouhavehereisagraphicalrepresentationofthe3Dcentroidthethreemeans(averages)ofthe900Cartesianpoints,thoughofcourseyoucannotseethealtitudedimension.UsePositionPropertiestoassessthealtitude.Whatisit?
ROOFMEAN.SSFrepresentsthebestapproximationyoucanmakeoftheactuallocationoftheantenna,ifallyouhavetogoonarethedatainB022721A.SSF.
WhenSAwentawaythingsgotbetteralotbetter.
NowthatSAhasbeenturnedoff,individualfixesarealmostalwaysclosertothetruepositionoftheantenna.Todemonstratethis,youwillsimultaneouslyopenthreefilestakeninthesameplaceastheoriginal,butwithouttheintentionalperturbationofSA.ThenyouwillaveragethefixesinthesefilesandlookathowtheycomparewithROOFMEAN.SSF.
{_}OpenthefilesA090214A,B,andCtogetheranddisplaythem.Measurethedistancebetweenthefixesfurthestapart.ComparethiswiththedistanceyoumeasuredbeforeforB022721A.SSF.Agreatimprovement,no?SointermsofrawfixescollectedbyaGPSreceiver,thevariancehasbeenimprovedbyaboutanorderofmagnitude(afactorof10).
{__}UsetheHelpmenutoreadabouttheCombinecommand(youuseditbefore)thatletsyouconcatenate16GPSfilessothattheyformasinglefile.ThencombineA090214A,B,andCtogethertoformROOF_NOSA.SSF.
{__}UsetheGroupingutilitytoproduceasinglepointfromthefixesofROOF_NOSA.SSFtoproduceROOFMEAN_NOSA.SSF.OpenROOFMEAN.SSFandROOFMEAN_NOSA.SSFandviewthem.Howfarapartaretheyhorizontally?
Acoupleofthingsareinterestinghere:Firstisthatthetwopointsaresoclosetogetherhorizontally,despitethelargespreadofthefixesofthefiles.Thoughwedontknowtheactualtruepointwecaninferthataveragingworks!Secondly,thealtitudesaremuchworsethanthehorizontaldistances.ThatissimplyacharacteristicofGPSthoughusuallytheerrorsarenotthisgreat.Bearinmindthatwehavenotyetappliedthecorrectionmechanismthatwehavewaitinginthewings.
PROJECT3CNewCircleRoad
Hereyouwillexamineanotherfiletakenwhilemovingtheantennaalongapath.Youwilllookatusingthe"Pan"and"AutopantoSelection"features.Additionallyyouwillgetanideaofhowdifferentialcorrectioncanimprovedataaccuracydramatically.
Lexington,Kentuckyiscircumscribedbya(mostly)limitedaccessringnamedNewCircleRoad.Unlikemanycities,Lexingtonsstreetpatternresemblesabicyclewheelspokesandrimratherthanagrid.Acarproceededfromthesouth,enteredthecircleroadheadingwest,andproceededaroundthecity,exitingateverymajorspoke,makinga"U"turn,andreenteringthecircle.TheprimaryresultsofthisoperationwereaGPSfilenamed
NEWCIRCLE.SSFandapolicewarningregardingillegal"U"turns.
{_}SetupLayersinViewsothatNotInFeaturefilesaredisplayedwithathingrayline.MaketheDistanceunitsMiles.
OpenNEWCIRCLE.SSFwhichyouwillfindin_:\GPS2GIS\CIRCLERD.TheplotshouldlooksomethinglikeFigure37.
{__}ZoomupsothatthesouthernmostareaoftheGPStrace,includingtheentirenorthsouthsegment,fillsthewindow.
{_}Movetheimageonthescreenusing"Pan":SelectPanfromtheViewmenuortheMouseBaricon.Placethecrosshairsonapointontheimage(somewhereotherthanthecenterofthewindow)andclick.Notethattheimageshiftssothatthepointselectedmovestothecenterofthewindow.Ifyoulosetheimagecompletely,usethe"ZoomtoExtents"tooltorecovertheentireimage.Thenzoomupagain.
{__}Aswithzoom,youcanalsousedragwithPanactive.SelectapointontheGPStrackanddragittoanydesirednewposition.Ifyoulosetheimagecompletely,usethe"ZoomtoExtents"tooltorecovertheentireimage.Thenzoomupagain.
6/29/2015 ExaminingGPSData(GPSandGIS)Part3
http://whatwhenhow.com/globalpositioningsystemandgis/examininggpsdatagpsandgispart3/ 5/6
{__}Usethe"Pan"tooltoslidetheimagenorthwardfromthesouthernmostpoint,thenwestwardaroundNewCircleRoadtothenextexit.Youcanseethetrackgoinguptherightsideofthearterialgoingnorthnortheast,andagainintherightsidecomingbackafterthe"U"turn.Youcanalsoimaginetheexitandentrancerampsleadingfromandreturningtothetrackofthelimitedaccessroad.Continuetopanaroundtheimageuntilyoufeelproficientwiththepanningtool.NowZoomtoExtentsand,withPositionProperties,selectthefirstpoint.
{_}Explore"AutoPantoSelection":IntheViewmenu,withtheMapwindowactive,putacheckbesideAutoPantoSelection,orclicktheAutoPanicontoturnthisfeatureon.UsePositionPropertiestoselectLasttoplaceamarkeronthelastpointoftheGPStrack.NowclickonFirst(theyareinaboutthesamelocationitwasacompletecircuit).ZoomIntightlyontheselectedpointagain.NowbeginchangingtheselectedpointwiththeNextbutton(">").Noticethatwhentheselectionwouldaddressapointthatisoutsidethewindow,theselectedpointismovedbacktothecenterofthewindow.Panpartwayaroundthecircleinthismanner,perhapswithdifferentlevelsofzoom.Notethatyoucantlosetheimage.Notealsothatitisprettyjaggedinspots.
{_}Addanewfiletothedisplayonethatmimicsthepreviousone,butwhosepositionshavebeencorrected:11OpenthefilesNEWCIRCLE.CORandNEWCIRCLE.SSFbyclickingontheminthatorder(withtheCtrlkeyhelddowntoselectthesecondone).SetupLayersinViewsothatLine_genericfeaturesareshownwithathinredline.(Notethatthefileselectedfirstislistedlastinthestringoffilenamestobeopened.)
Figure37.GPStrackaroundNewCircleRoad.
Butitisinstructiveforyoutoseetheresults,especiallysincethedatayoutookinProject2Bmayturnouttobedisappointing.
{__}ZoomupagainonthesouthernareaandusePositionPropertiestoselectthe"First"point.BesurethatAutoPanison.Beginmovingalongthetraceasbefore.Toseetheimprovementcreatedbycorrectingthedata,notetheunevennessofthegrayline,comparedtotheredone,alongthefirstpartofthepath.AlsonoticethelittledetourthegraylinetakesjustpriortothepointwherethecarentersNewCircleRoad.
{__}UndertheFilemenuclickClose.Themapwindowwillbecomeblank.
PROJECT3DSAGoesAwayBackgroundFilesHelpYouSeeItOn1May2000theWhiteHousesuddenlyannouncedthatselectiveavailability(SA)wouldbeturnedoff.ThetransitiontookplacejustaftermidnightEasternDaylightTimeonTuesday2May2000.Closertohome,afilewascreatedusingaGeo3,withtheantennaatafixedlocation,fromabout11:30P.M.on1Mayuntilabout12:30A.M.on2May.ThefilesBEFORE.SSFandAFTER.SSFwerecreatedbydividingthatfilewiththeRecordEditoraPathfinderOfficeUtilityProgramthatwillbedescribedshortly.ThepointofdivisionwasthetimeatwhichSAwasturnedoff.
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6/29/2015 ExaminingGPSData(GPSandGIS)Part3
http://whatwhenhow.com/globalpositioningsystemandgis/examininggpsdatagpsandgispart3/ 6/6
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{_}MakeaProjectnamedByeByeSA_yis.Haveitreferto_:\GPS2GIS\ByeByeSA.
{__}SettheTimeZonetoEasternDaylight.
{_}StartingwithFile~Open,examinethecontentsofthefolderByeByeSAin__:\GPS2GIS.OpenBEFORE.SSF.Note,byclickingonFirstandLastinthePositionPropertieswindow,thatthisfileconsistsoffixestakenonMay1st,approximatelybetween11:30P.M.andmidnight.Measurethespreadoffixes.Whatdistanceistherebetweenthefarthestapartpoints?
YouwouldliketocontrastBEFORE.SSFwithAFTER.SSF.WecouldopenthesetwofilestogetherbutsincetheyarebothNotInFeaturefilesitwouldbehardtoseethemdistinctlyasseparate.Wewouldliketoseethemwithdifferentsymbolizationsowecouldcomparethem.Asbefore,wecouldmakeoneaLine_Genericfile,butletsexamineanotherway.PathfinderOfficeallowsyoutodisplayafileinthe"background"thatis,thevisualaspectsofthefileappearsintheMapwindow,butnofeaturesinthefileareselectable.Wewillusethis"background"abilitytodisplaythefileAFTER.SSF.
{_}UsingtheUnitsandCoordinateSystemchoicesundertheOptionsmenu,setuptheproperparametersforthisproject:SettheOptionstoU.S.StatePlane1983coordinatesystem,KentuckyNorthZone(1601).ThedatumisNAD1983(Conus).TheDistanceunitsandCoordinateunitsareSurveyFeet.TheTimeZoneremainsEasternDaylight.
{_}UsingView~Layers~FeaturesmakeNotInFeaturedataappearasathinredline.
{_}UsingFile~Background,checktoseeifanyfilesareinthelistofbackgroundfilestoload.HighlightanysuchfileidentifiersandclickRemovetoemptythewindow.Nowclick"Add"andnavigateto__:\GPS2GIS\ByeByeSA\AFTER.SSFandpounceonit.OkaytheLoadBackgroundFileswindow.UnderView~Layers~Background,chooseamoderatelythingreenlinetorepresentNotInFeaturedata.Onceitloadsyoushouldseeagreenblobsurroundedbyredlines.Zoomuponthegreenareaandmeasurethespreadoffixes._.Quiteanimprovement!
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