GPS and GIS

6/29/2015 ExaminingGPSData(GPSandGIS)Part3

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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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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.



{_}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



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.



{__}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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{_}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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