The GPlates Portal: Cloud-Based Interactive 3D Visualization of Global Geophysical and

17 Pages·2016·14.68 MB·English

RESEARCHARTICLE
The GPlates Portal: Cloud-Based Interactive
3D Visualization of Global Geophysical and
Geological Data in a Web Browser
R.DietmarMüller1*,XiaodongQin1,DavidT.Sandwell2,AdrianaDutkiewicz1,Simon
E.Williams1,NicolasFlament1,StefanMaus3,MariaSeton1
1 EarthByteGroup,SchoolofGeosciences,TheUniversityofSydney,Sydney,NSW2006,Australia,
2 ScrippsInstitutionofOceanography,LaJolla,California,92093,UnitedStatesofAmerica,3 CIRES,
UniversityofColoradoatBoulder,Boulder,Colorado,80309,UnitedStatesofAmerica
*[email protected]
Abstract
Thepaceofscientificdiscoveryisbeingtransformedbytheavailabilityof‘bigdata’and
OPENACCESS openaccess,opensourcesoftwaretools.Theseinnovationsopenupnewavenuesforhow
scientistscommunicateandsharedataandideaswitheachotherandwiththegeneralpub-
Citation:MüllerRD,QinX,SandwellDT,Dutkiewicz
A,WilliamsSE,FlamentN,etal.(2016)TheGPlates lic.Here,wedescribeoureffortstobringtolifeourstudiesoftheEarthsystem,bothatpres-
Portal:Cloud-BasedInteractive3DVisualizationof entdayandthroughdeepgeologicaltime.TheGPlatesPortal(portal.gplates.org)isa
GlobalGeophysicalandGeologicalDatainaWeb
gatewaytoaseriesofvirtualglobesbasedontheCesiumJavascriptlibrary.Theportal
Browser.PLoSONE11(3):e0150883.doi:10.1371/
journal.pone.0150883 allowsfastinteractivevisualizationofglobalgeophysicalandgeologicaldatasets,draped
overdigitalterrainmodels.TheglobesuseWebGLforhardware-acceleratedgraphicsand
Editor:JuanA.Añel,UniversidadedeVigo,SPAIN
arecross-platformandcross-browsercompatiblewithcompletecameracontrol.Theglobes
Received:December6,2015
includeavisualizationofahigh-resolutionglobaldigitalelevationmodelandtheverticalgra-
Accepted:February19,2016 dientoftheglobalgravityfield,highlightingsmall-scaleseafloorfabricsuchasabyssalhills,
Published:March9,2016 fracturezonesandseamountsinunprecedenteddetail.Theportalalsofeaturesglobespor-
trayingseafloorgeologyandaglobaldatasetofmarinemagneticanomalyidentifications.
Copyright:©2016Mülleretal.Thisisanopen
accessarticledistributedunderthetermsofthe TheportalisspecificallydesignedtovisualizemodelsoftheEarththroughgeologicaltime.
CreativeCommonsAttributionLicense,whichpermits Thesespace-timeglobesincludetectonicreconstructionsoftheEarth’sgravityandmag-
unrestricteduse,distribution,andreproductioninany
neticfields,andseveralmodelsoflong-wavelengthsurfacedynamictopographythrough
medium,providedtheoriginalauthorandsourceare
credited. time,includingtheinteractiveplottingofverticalmotionhistoriesatselectedlocations.The
globesputtheon-the-flyvisualizationofmassivedatasetsatthefingertipsofend-usersto
DataAvailabilityStatement:Thedatadisplayedon
thevirtualglobesareallpublishedandfreely stimulateteachingandlearningandnovelavenuesofinquiry.
available,butatanumberofdifferentinternetsites.
Linkstoallrelevantsitescanbefoundontheweb
pagesfortheindividualvirtualglobesontheGPlates
Portalathttp://portal.gplates.org/.Summary:Gravity
grid,http://topex.ucsd.edu/grav_outreach/,Owner:
Introduction
ScrippsInstitutionofOceanography,Contact:David
Sandwell,[email protected];Magneticgrid,http://
Geosciencereliesheavilyonthevisualizationofgeospatialdata,helpingustomakefundamen-
geomag.org/models/emag2.html,Owner:National
talnewinferencesabouttheEartharoundus,andhowithasevolved.Morethan100yearsago,
OceanicandAtmosphericAdministrationoftheU.S.
AlfredWegener[1]proposedthetheoryofcontinentaldriftbyestablishingpreviouslyunrec-
DepartmentofCommerce,Contact:StefanMaus,
[email protected];SRTL15Plus ognisedassociationsbetweengeologicalandfossildatafromwidelydispersedcontinents,and
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Cloud-BasedInteractive3DVisualizationofGeodatainaWebBrowser
topography,http://topex.ucsd.edu/www_html/srtm30_ fittingtogetherthebathymetricoutlinesofthesecontinentsdefinedwithinmapsoftheEarth.
plus.html,Owner:ScrippsInstitutionof Today,scientistshavevastquantitiesofdataattheirdisposaltopursuenewtheoriesofthe
Oceanography,Contact:DavidSandwell, Earthsystem—theEarth’ssurfaceiscontinuouslymonitoredbysatellites,geologicalsampling
[email protected];Seafloorlithologygrid,http://
fromlandandseaisbeingassembledintocommunitydatabases,geophysicalimagingprobes
www.earthbyte.org/seafloor-lithology-of-the-ocean-
basins/,Owner:TheUniversityofSydney,Contact: present-daydeepEarthstructure,andsupercomputingresourcespowerdynamicsimulations
AdrianaDutkiewicz,[email protected]. ofthephysicalprocessesshapingtheworldaroundus,overtimescalesuptohundredsofmil-
au;Platereconstructionsusedtoreconstructthe lionsofyears.Theseadvancesalsocreatenewproblemstosolve—howcanscientistsefficiently
gravityandmagneticgrids,http://www.earthbyte.org/
shareandcommunicatethesedatasetswitheachother,andwithnon-specialists,tomaximise
global-continental-and-ocean-basin-reconstructions-
thepublicbenefitofthelargeeffortsundertakenincreatingthesedatasets?
since-200-ma/,Owner:TheUniversityofSydney,
Virtualglobeshavechangedthewayweinteractwithspatialdata,largelyduetothepopu-
Contact:DietmarMüller,[email protected].
au;Dynamictopographygrids,http://www.earthbyte. larityofGoogleEarth[2]andNASAWorldWind[3].Followingthebroaduptakeofthese
org/a-review-of-observations-and-models-of- technologiesbyscientistsandend-users,alternativetechnologiesforvirtualglobeshavebeen
dynamic-topography-2013/,Owner:TheUniversityof developedthatarefasterfordisplayingofverylargedatasets(e.g.,fordetailed3Dtexturedcity
Sydney,Contact:NicolasFlament,nicolas.
models[4]),workwellonhand-helddevices,andcanfunctionentirelywithinaweb-browser.
[email protected];Magneticanomaly
Thesealternativetechnologiesalsoprovidepowerfuladditionalfunctionality,forinstanceuse
identifications,http://www.soest.hawaii.edu/PT/
GSFML/ML/index.html,Owner:Numerousauthorsof ofcustomimageryandterrainmodelswithgreateruser-controlofverticalexaggeration;aded-
paperslistedonwebsiteabove,Contact:Maria icatedinfrastructurefordisplayingtime-dependentdatasets;andtheabilitytoproducecustom
Seton,[email protected]. user-interfaces,specificallydesignedtoshowcasetheresultsofaparticularstudyorproject.
Funding:Thisprojectwassupportedbythe TheseandotherrequirementshavepromptedthedevelopmentoftheCesiumsoftwarelibrary
AuScopeNationalCollaborativeResearch (cesiumjs.org).
InfrastructureandaBigDataKnowledgeDiscovery Here,wedescribenoveldevelopmentsintheuseofCesiumvirtualglobestoenableweb-
project(SIEFprojectRP04-174),Australian
basedvisualizationandknowledgediscoveryforarangeofapplicationsinthegeosciences.We
ResearchCouncilgrantFT130101564(MS),
havecreatedtoolsthatallowend-userstointeractwithdatasetsthatdescribetheEarthasitis
AustralianResearchCouncilgrantFL0992245
now,basedonremotesensingdata,marinegeophysicaldataandanovelapproachofmapping
(RDM),ScienceIndustryEndowmentFundgrantRP
04-174RDM,andanARCLaureateFellowship seafloorlithology.Inaddition,ourvirtualglobesallowtheusertovisualizeEarth’splatetec-
(FL0992245)andtheAuscopeNationalCollaborative tonicevolutionthroughdata-drivenreconstructionsofsupercontinentdispersalandglobal
ResearchInfrastructure.Theauthorsalso numericalmodelsdescribinghowmantleconvectionhasshapedtheEarth’ssurfacethrough
acknowledgesupportbytheNectarCloudandthe
time.Wediscussthetechnicaldetailsrequiredtoimplementthesetools,andillustratehow
AustralianNationalDataService(ANDS).
theycanhelptoincreasepublicengagementwithgeoscience,andpromotecross-disciplinary
CompetingInterests:Theauthorshavedeclared researchbymakinggeospatialdatasetsmoreaccessibletoawideaudiencewithinthescientific
thatnocompetinginterestsexist.
community.
TechnicalBackground
SystemArchitecture
Cesiumisanopen-sourceJavaScriptlibrarybuiltontheWebGraphicsLibrary(WebGL)for
interactivevisualizationof3Dglobesand2Dmapsinawebbrowser.WebGLisawebstan-
dard,designedandmaintainedbytheKhronosGroup(www.khronos.org),forlow-level3D
graphicsApplicationProgrammingInterface(API)basedonOpenGLES2.0–astandardAPI
for2Dand3Dgraphicsonembeddedsystems[5].ThewebbrowsersimplementWebGLAPI
asaDocumentObjectModel(DOM)interfaceinHTML5[6]Canvaselements,whichallows
JavaScriptprogramstoutilizeGraphicsProcessingUnit(GPU)for3Dgraphicshardware
acceleration.WebGLsupportiswidelyavailableinmodernbrowsers,suchasGoogleChrome,
MozillaFirefox,Safari,andothers.Asavirtualglobeandmapengine,Cesiumutilizesa
WebGLAPItoprovidefast,cross-platform,cross-browserandplugin-free3Drenderingfunc-
tionality,whichmakesitidealforthedevelopmentofinteractive3Dglobalgeophysicaland
geologicaldatavisualizationwebapplications.
TheGPlatesPortal(portal.gplates.org)isdesignedwithathree-layeredarchitectureconsist-
ingofpresentation,logicanddatalayers.Thelayerisalogicalconceptofcomponentgroups,
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Fig1.TheGPlatesPortal’smultilayeredarchitecture.Athree-layeredarchitectureconsistsof
presentation,logicanddatalayers.ThepresentationlayerincludestheGraphicalUserInterface(GUI)and
themaincanvasfor3Drendering.ThelogiclayercontainsanumberofwebserviceswritteninPythonand
deployedinDjangoWebFramework[7].Thedatalayerfocusesonthestorageandretrievalofdata.
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whichdividesalargesystemintodifferentareasoffunctionalitysothatthecomplexityofthe
systemcanbeminimizedandeachlayercanbedesignedandimplementedseparatelyandeffi-
ciently.Thismultilayerarchitecturealsoprovidesthehighestlevelofencapsulationandisola-
tion,whichdecouplesthesystemandreducestherippleeffectofchangestothesystem.Fig1
illustratesthemultilayeredsystemarchitectureoftheGPlatesPortal.
ThepresentationlayerincludestheGraphicalUserInterface(GUI)andthemaincanvasfor
3Drendering.TheGUIisdevelopedwithHTML5,JavaScriptandCascadeStyleSheet(CSS)
andcanbeusedtocontrolthemaincanvasanddisplayadditionalinformation.ThejQuery
JavaScriptlibraryisusedtohelpwiththeclient-sidescriptingandtheCesiumlibraryisusedto
drawthe3DvirtualglobeandmapsonanHTML5Canvas.
ThelogiclayercontainsanumberofwebserviceswritteninPythonanddeployedinDjango
WebFramework[7].TheApacheHTTPServerisusedtohandletheHTTPprotocolbetween
theDjangoWebFrameworkandclients.TheHTTPrequestsaredispatchedtocorresponding
webservicesbytheDjangoWebFrameworkandtheHTTPresponsesaredeliveredbacktocli-
entsthroughthesamestack.
Thedatalayerfocusesonthestorageandretrievalofdata.Asetofdatasourceadaptersis
createdtodecouplethewebservicesfromthedatastoragedetails.Thedatasourceadaptersread
aDataSourceDescription(DSD)fileinJSONformattoretrieveandfeeddatabacktowebser-
vices.Thewebservicesonlyinteractwithanabstractinterfaceofdatasourceadapters,soany
changestothedatastoragearecompletelytransparenttothewebservice.Thisdecoupling
allowsustochangethedatastoragedetailswithoutaffectingthewebservices.Currently,our
datasourcesincludefilesonlocalvolumes,tablesinaPostGIS[8]database,objectsinAmazon
SimpleStorageService(S3)[9]andsomeexternaldatasourceshostedbycollaborators.
Benefitsofthe“SoftwareasaService”model
Easyaccess. Userscanstartusingtheapplicationswithouthavingtogothroughasoftware
installationprocess.Theapplicationscanbeeasilyaccessed,especiallyforuserswhohaveto
facethestrictsoftwareinstallationpolicyoftenimposedbyITdepartmentofsome
corporations.
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Automaticupgradeandmaintenance. Becausethesoftwareapplicationsarecentrally
hosted,theycanbeeasilyupgradedbytheserviceproviders.Allusersusethesameversionofa
software,whichmakescollaborationbetweenuserseasierbecausetherearenoproblemswith
softwareversionmismatches.Bugfixescanbedeliveredquicklyandeasily.Usersdonothave
towaitforthenextreleasetogetthebugsfixed.
Connectivityandresourcessharing. IntheInternetera,itisimportantthatresourcesare
connectedandshared.Theresources,suchascomputation,storageandsoftwarefunctionality,
canbeutilizedmoreefficientlyinaconnectedenvironmentanduserscancollaboratemore
efficientlybecausedataareconnectedandshared.
Platformindependence. UsersonlyneedanInternetconnectionandawebbrowserto
accesstheGPlatesPortal.Thereisnosignificantplatformrestriction.TheCesiumwebapplica-
tionsharnessmoderntechnologytogiveusersaninteractive3Dexperience.Userscanrotate
theglobe,adjusttheangleofview,changetheheightscale,andzoomintotheverydetailsof
highresolutionrasterandterrain.Someportalapplicationsareabletocalculatedataataspeci-
fiedtime/ageaccordingtotheuserinput.
CloudHosting. TheGPlatesPortalishostedinthecloud.Cloudhostingprovidesthefol-
lowingadvantages,comparedwithtraditionalon-premisesinstallation:
1. Scalabilityandflexibility.Thetraffictoourwebservicesishighlyvariable.Spikesinthe
numberofpagerequestscoincidewiththepublicationofdatasetsassociatedwithhigh-
impactjournalarticles,whenthearticlesattractwide-spreadmediaattentionandgeneral
publicinterest.Inlightofthevariableusage,itisimportantforthesystemtoadjustits
capabilityon-demand.TheCloud’sAutoScalingserviceallowsustoscalethesystem’s
capacityupordownautomaticallyaccordingtotheconditions.Thisautoscalingabilityis
importanttoensurethequalityofourwebserviceswithoutincurringasubstantialinfra-
structurecost.
2. Lowercostandpayasyougo.Usingcloudhostingkeepsthecostofhardwarepurchase
andmaintenancetoaminimum.Furthermore,unneededvirtualmachinesintheCloud
canbeterminatedatanytime,thuseliminatingtheissuesrelatedtodisposalofcomputer
hardware.
3. Launchvirtualmachineatdesignatedlocations.Thereisanobviouspatterninthedistribu-
tionofuserlocations,whicharemostlywithinAustralasia,EuropeandtheUSA.TheCloud
allowsustolaunchvirtualmachinesinthesedesignatedregionstoimprovethespeedof
networkaccess.
FreeSoftwareforGlobeDesign
Oneofthebasicprinciplesofthescientificmethodisthatresearchresultsshouldbereproduc-
ibleandindependentlyverifiable[10]andoneofthekeycomponentsofreproducibilityis
opensoftware.FreesoftwareisusedinthedevelopmentoftheGPlatesPortal,whichgives
readerseasyaccesstothetoolsrequiredtorepeatthemethoddescribedinthispaper.The3D
renderingengine,CesiumVersion1.7.1(http://cesiumjs.org/downloads.html),isreleased
undertheApache2.0license.Thereconstructionengine,GPlates/PyGPlatesVersion1.5
(http://gplates.org/download.html),isreleasedunderGPLv2.TheauxiliaryPythonprograms
inS1ArchivearereleasedunderGPLv2inaccordancewithGPlates.ThematplotlibPython
libraryversion1.5.1(http://matplotlib.org/1.5.1/index.html)isreleasedunderthePythonSoft-
wareFoundation(PSF)license.
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Fig2.Workflowfordesigningavirtualglobe.ThedetailsinvolvedinthisworkflowaresummarizedinS1Text.
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VirtualGlobeDesignandConstruction
Introduction
Virtualglobedesignandconstructionconsistsof4majorsteps(Fig2):(1)preparingimagery
tiles,(2)preparingterraintiles,(3)servingimageryandterraintilesovertheinternet,and(4)
buildingtheapplication.Thedetailedmethodologyinvolvedindesignandconstruction,
includingpythonscripts,isavailableinS1Textandsupplementarypythonscriptsarearchived
inS1Archive.
Designandfunctionalityofindividualvirtualglobes
Inthefollowingsectionswedescribeaseriesofvirtualglobesthatwehavecreatedaspartof
theGPlatesPortal.Eachglobeisacompaniontoapublishedscientificresearcharticle.Indeed,
eachglobecanberegardedasapowerfulsupplementaryresourcetothesestudies,allowing
anyonewithawebbrowsertovisualizeandinteractwithlargedatasets,reconstructions,and
geodynamicsimulationoutputthatcanonlybepartlyrepresentedwithinthelimitationsofa
journalarticle.
High-resolutiontopographyandbathymetry
TherearemanyEarthprocessesthatcanonlybeunderstoodbymappingthetopographyofthe
deepoceansathighresolution.Theseincludesmall-scalefeaturessuchasabyssalhills,small
seamounts(<1kmtall),fracturesthatformontheouterwallsofdeepoceantrenches,andthe
erosionalincisionsontheseawardslopesofthecontinentalmargins.Anewglobalgridofland
topographyandoceanbathymetrycalledSRTM15_PLUS(15arcsecondresolution)was
recentlydeveloped[11]followingthemethodsoftheSRTM30_PLUSgrid[12].Thelandtopog-
raphyisbasedontheSRTM3mappingbythespaceshuttlein2000[13].Thisisaugmentedby
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high-latitudedatafromASTERstereotopographyandacombinationofCryoSAT-2andIce-
SATaltimetrydatafortheicecapsofGreenlandandAntarctica.Thenewaspectofthegridis
theglobalbathymetrywhichisbasedonpublicallyavailabledepthsoundingsfromawidearray
ofsourcescombinedwiththelatestglobalbathymetricpredictionfromtheglobalmarinegrav-
itygriddiscussedabove[14].Inparticular,high-resolution(100–200m)multibeamecho
sounderdatafromoceanographicinstitutionsaroundtheworld[e.g.,Lamont,Scripps,Woods
Hole,JAMSTEC,GEOMAR,IFREMER,etc.]coverabout11%oftheareaoftheoceansat15
arcsecondresolution(~500m).Theoldersingle-beamsoundingsfromaglobalcompilation
maintainedattheUSNationalGeophysicalDataCenterprovide1kmspatialresolutionoveran
additional6%oftheseafloor.Depthsontheremaining83%oftheseafloorareinterpolated
fromtheglobalgravitygrid[15].Thiswidevarietyofdatawasassembledusingtheremove/
restoremethodtobootstrapfromtheSRTM15_PLUScompilation.Theassemblymadeexten-
siveuseofGenericMappingTools[16]forgriddingaswellasmaskingland/oceanareas.The
SRTM15_PLUSgridwillformthebasisforthenextversionofGoogleEarthandispublicly
availableatftp://topex.ucsd.edu/pub/srtm15_plus/.
Whileallofthesourcedataarepubliclyavailableandhavebeenanalyzed,theglobalassem-
blyprovidesanewperspectiveonseveraltypesofoceanfeatures.First,thespatialvariationsin
abyssalhillfabric,notwellresolvedat30arcseconds,arenowvisiblealongmostoftheseafloor
spreadingridgeaxesaswellassomewellsurveyedareaswiththinsedimentcover.Theampli-
tudeandorientationofthisabyssalfabricprovidesawindowintothepastspreadingrateand
direction.SignificantnewmultibeamcoveragefromJAMSTECintheWesternPacificprovides
remarkableresolutionoftheIzu-BoninandMarianatrenches,PhilippineSeaandPareceVela
Basin(Fig3).ArecentcompilationofmultibeambathymetryfromGeoscienceAustralia
(http://www.ga.gov.au/scientific-topics/marine/bathymetry)providesvastlyimproved
Fig3.SRTM15PLUSCesiumglobenorthwardviewoftheregionaroundtheMarianaArcandTrench.Recentlyaddedmultibeambathymetrydata
havesubstantiallyincreasedresolutionofsmall-scalefeaturesinthisregion.
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resolutionofthecontinentalmarginsandcontinentalrisearoundAustralia.Newmultibeam-
basedgridsfromGEOMARrevealthedetailedstructureoftheCentralChileTrenchandouter
trenchwall.
Seafloorlithology
Theworld’soceanfloorisdrapedbyavastblanketofsediments,whichformsthelargestgeo-
logicaldepositandthelargestcarbonsinkonEarth(Fig4).Thecompositionofthesesedi-
mentsishighlyvariableandincludesremainsofplanktonthathavesettledthroughtheocean
column,terrigenousparticlesderivedfromcontinentsandchemicalprecipitatesthathave
formedinsituontheseafloor.Thedistributionofthesesedimentsiscriticalforunderstanding
howEarthhasrespondedandcontinuestorespondtoenvironmentalchanges,thebehaviorof
oceancurrents,theoccurrenceofmetaldepositsandtheassessmentofgeohazards.Therecent
publicationofthefirstdigitalmapofseafloorsedimentsbasedontheanalysisandclassification
ofnearly15,000surfacesedimentsamples[17],providesalongoverdueupdateonahighly
generalizedhand-drawnmapofglobalseafloorsedimentsthatdatesbackto1974[18]andfea-
turesinvirtuallyeverytextbookofmarinegeologyandoceanography.Thedigitalmapwascre-
atedusingabespokemachine-learningalgorithm[17]andallowsthejointanalysisofthese
categoricaldatawithoceanographicdatathatarefreelyavailable,forinstance,throughthe
NationalOceanicandAtmosphericAdministration(NOAA)(www.nodc.noaa.gov/OC5/
WOD/pr_wod.html).Beingopen-access,thedigitalmapisavaluableresearchresourcefor
Fig4.Cesiumglobeviewofseafloorsedimenttypesdrapedoveradigitalelevationmodelwithanoverlayofmajorrivers(bluelines).Several
featuresofinterestarehighlighted.
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geologists,oceanographersandclimatologists,andithasbyfarthehighestviewingrateofthe
portal’svirtualglobesatanaverageof~500viewsperdaysinceAugust2015.Inits3Dvisuali-
zationformatthatalsofeaturesanoptionaloverlayofworld’smajorrivers,itisapowerfuland
excitingteachingtoolforalllevels.Asseafloorlithologyisdrapedoveradigitalterrainmap,
theglobeallowstheviewertoexplorehowthedistributionofdifferentsedimenttypesvaries
betweenoceanbasinsandwithlatitude,formingthebasisformakingconnectionswithavari-
etyofprocessesthatgovernthedistributionofeitherbiogenicorlithogenoussediments.For
instance,theglobecanbeusedtoexplorehowthetypeofseafloorsedimentdependsonprox-
imitytomid-oceanridges,volcanicplateaus,differenttypesofcontinentalmargins(tectoni-
callypassiveoractive),majorrivermouthsanddifferentclimaticzones.
Verticalgravitygradient
Gravitymodelsarepowerfultoolsformappingthestructureoftheoceanfloor,especiallyinthe
deepoceanbasinswherethetopographyremainsunmappedbyshipsorisburiedbythicksedi-
ments.Arecentlypublishedglobalmarinegravitymodel[14],whichistwiceasaccurateaspre-
viousmodels,hasherebeencombinedwiththecontinentalgravitymodelEGM2008[19]to
produceaglobalmodelforthefree-airgravityfield.Thedigitalfree-airgravitymodelwasused
tocomputetheverticalgravitygradient,whichenhancessmall-scalegravityanomalies,related
totectonicstructuressuchassmallseamountsandfaults,horstandgrabenstructuresatthesea-
bedorburiedunderneaththeseafloor.Theverticalgravitygradientisparticularlyusefulfor
visualizingdeepstructuresassociatedwithcontinentalmarginsandsedimentarybasins,where
seismicimagingdataaresparseandexpensivetoobtain.Theverticalgravitygradientdataset
wasusedtocreatethefirstoftheGPlatesPortalvirtualCesiumglobesinOctober2014;ithas
sincebeenviewednearly100,000times(31stJanuary2016).Whilethousandsofmetersofwater
obscureourviewofthearrayofgeologicalfeaturescharacterizingtheseabedandburiedsub-
seafloorgeology,themarineportionofthisgloberevealsmanypreviouslyunknownseafloor
andsub-seafloorstructures,includinganextinctmid-oceanridgefromtheJurassicPeriodin
theGulfofMexico(nowburiedbyupto8kmofsediments)andahugeancientriftscarinthe
SouthAtlanticOceanformedbyadeep-seated“hotspot”leadingtoacrackingoftheoceanfloor
[14].Byprovidingaseamlessviewofthecombinedmarineandcontinentalgravityfield,this
Cesiumglobeallowstheusertofollowstructuresfromthedeepoceanbasinstocontinental
slopesandshelvestothecontinentsthemselves.Suchstructuresmayincludeoceanicfracture
zones,manyofwhichhaveanoriginintectoniclineamentsinthecontinentalcrustwhich
existedbeforecontinentalbreakup[20],aswellasmeteoriteimpactstructures(Fig5).
Globalmagneticanomalies
Ferrousmineralsinthecrustanduppermantlegiverisetomagneticanomalies.Thestrength
andshapeoftheseanomaliesreflectsthemineralogyandthicknessofgeologicalformations.
Sincemineralsbecomenon-magneticabovetheirCurietemperature,magnetizationhasalim-
iteddepthextent,whichdependsonthelocaltemperaturegradientofthelithosphere.Mag-
neticanomaliesthereforeprovideinsightintosubsurfacestructure,compositionandheatflow
intheEarth'scrust.Anomaliestrendingparalleltotheisochrons(linesofequalage)inthe
oceansrevealtheformation(seafloorspreading)anddestruction(subductionzones)ofoceanic
crust,theformationofcontinentalcrustbyaccretionofvariousterranestocratonicareasand
large-scalevolcanismoncontinentsandintheoceans.
Magneticanomalydatahavebeencollectedbyships,aircraft,andlow-orbitingsatellitesfor
morethanhalfacentury,providingglobalcoverageoftheEarth.TheEarthMagneticAnomaly
Gridin2arcminuteresolution(EMAG2)istheresultofaninternationalcollaborationbased
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Fig5.CesiumglobesoutheastwardviewoftheGulfofMexicoandtheYucatanPeninsulawheretheverticalgravitygradientgrid,overlainbya
digitalelevationmodel,revealstheburiedcircularstructurerelatedtotheChicxulubImpactCrater(CIC)thatledtotheextinctionofthedinosaurs
andmanyotherspecies,straddlingthecoastlineoftheYucatanPeninsula[21].Impact-generatedmulti-ringgravityanomaliescanbeusedtocompute
theimpact’ssizeandothercharacteristics[21].TheimagealsorevealstheburiedextinctJurassicmid-oceanridge(MOR)oftheGulfofMexico[14].
doi:10.1371/journal.pone.0150883.g005
oncontributionsfromoveronehundreddataprovidersworldwide[22].Theinputdatacon-
sistedofboth2Dgridsand1Dprofiledatafromshipandairbornemeasurements.Thesewere
processed,linelevelledandmergedat4kmaltitudeusingleastsquarescollocation.Twover-
sionsoftheEMAG2gridwereproduced.Onewithconventionalisotropicgriddingandone
withanisotropic(directional)griddingovertheoceans,inwhichtheanomalieswere“stretched
out”inthedirectionofthelocalisochronsasgivenbytheoceaniccrustalagemodel[23].A
comparisonofEMAG2withandwithoutdirectionalgriddingisshowninFig6.Finally,contri-
butionswithspatialwavelengthslargerthan330kmwerereplacedwiththeCHAMPsatellite
magneticanomalymodelMF6[24].
Globalmagneticanomalyidentifications
Marinemagneticanomalyidentificationsareoneoftheprimarybuilding-blocksofglobalplate
reconstructions,usedtodeterminetheageoftheoceaniccrustandtounderstandpastsea-
floor-spreadingprocesses.Thesemagneticanomalyidentifications,oftencalled“magnetic
picks”,areaspatio-temporalrepresentationofinterpretedmarinemagneticanomalies
describedaboveagainstageomagneticreversaltimescale.Inthepast,mostglobalandregional
compilationshavebeenpresentedasaseriesofmapswithnoaccompanyingdigitaldata.An
open-source,community-driveninfrastructurecontainingover96,000publishedmagnetic
anomalyidentificationswasrecentlyestablished[25].Therepositorycontainsconsistently
describedandwell-documenteddatapointsthathaveundergoneinternalquality-control.
Whileallthedatahavebeenmadeaccessibletothepublicviaadedicatedwebsite(www.soest.
hawaii.edu/PT/GSFML),therepositorylacksavisualizationtoolforexpertandnon-expert
userstoviewandinterrogatethedata.ThesedatacanbevisualizedintheCesiumglobeatthe
PLOSONE|DOI:10.1371/journal.pone.0150883 March9,2016 9/17
Cloud-BasedInteractive3DVisualizationofGeodatainaWebBrowser
Fig6.IdenticalviewillustratingthedifferencebetweentheEMAG2versionwithdirectionalgridding
(top)andwithisotropicgridding(bottom).TheobserverlocationissouthofNewZealandlooking
westwardattheSouthernOcean,withAntarcticaonthesouthernsideandAustraliaonnorthernsideineach
image.
doi:10.1371/journal.pone.0150883.g006
PLOSONE|DOI:10.1371/journal.pone.0150883 March9,2016 10/17