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Cranialshapeevaluation573SUPERIMPOSITIONOF3DPHOTOGRAPHSForadequateanalysisevery3Dphotographneededtobepositionedinthesamecoordinate system and therefore rotations and translations needed to be eliminatedToachieve thisall3Dphotographswereimportedinto the3DMDPatientsoftware(3dMDAtlantaGAUSA)Eightanatomicallandmarksweremanuallyidentifiedonthe3Dphotographs(Table1)The3DphotographsandlandmarksweresubsequentlyexportedtothetechnicalcomputingsoftwareMatlab(MATLABv2012b TheMathworksIncNatickMAUSA)InMatlab ahorizontalplane definedbytheexocanthionendocantionandpretragionpointsandaverticalplaneperpendiculartothehorizontalplaneandpositionedthroughthesubnasalpointweregeneratedBasedonthemethoddescribedbyBronsetaltheplaneswereusedtoeliminatetherotations9(Figure1)All3Dphotographsweretranslatedtotheoriginofthereferenceframeusingthecomputedcranialfocalpoint(CCFP)presentedbydeJongetal10 Thisresultedinadatasetof3DstereophotographsinthesamecoordinatesystemwithoutrotationalandtranslationaldifferencesRESAMPLINGANDSCALINGAllthealignedandcorrectlypositioned3Dphotographsconsistedofadifferentnumberofvertices(3Dpoints)Forfurtheranalysisofthe3Dphotographsitwasrequiredtocreatemeshdatawiththesamenumberofverticesandthereforearesampling wasappliedResampling wasdoneusingareferenceshapeconsistingofahemi-icosphereintheformofacranialshapeandaraycastingalgorithm11Atotalof4501rayscastfromtheoriginofthereferenceshapewereusedandthereforeeverycranialshapeconsistedof4501verticesafterresamplingThevolumeofeverycranialshapewascalculatedusingthehorizontalplaneasalowerboundaryFinallyeverycranialshapewasscaledtowardsthesamevolumetoeliminatedifferencesincranialsizeAscalingidenticalineverydirectionwasusedwhichadjustedonlythesizeandpreservedtheshapeofthemodified3DphotographsPRINCIPALCOMPONENTANALYSISPCAisastatisticalmethod whichcandescribealargenumberofhighdimensionaldatawithasmallernumberofrelevantparameters12–143DphotographsofapopulationcanbeanalysedbyPCAtofindandisolatethedifferentvariationsofthe3Dshapesin thispopulationPCAcanbeused toextractonly therelevantandmostprominentvariationssuchasthelengthoftheskullanddisregardminor
