CCD stereo vision measurement system theory.docx
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CCD stereo vision measurement system theory.docx
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CCDstereovisionmeasurementsystemtheory
CCDstereovisionmeasurementsystemtheory
Abstract:
UsingtheprinciplesofgeometricalimagingCCDstereovisiontobuildamathematicalmodelofmeasurementsystems,improvetheprecisionofthesystemfromthestart,intheory,focusonsystemparameters,imagerecognitionerrorsandtherelationshipbetweentheprecisionofthesystemhasin-depthanalysisandExploreandexperimentontheconclusionwasverified.Researchontheactualestablishmentofthissystemhasastrongguidingrole.
Keywords:
stereovision;CCD;measurementaccuracy;imagerecognition;systemmeasurements
Introduction
Stereoscopicmeasurementincomputervisiontechnologyisanimportantbranchofcomputervisionhasbeenthefocusofthestudyandthehotspots.Duetoitssimilartothehumanvisualsystemwithhighprecisionandspeed,andhasasimplestructure,easytouse,etc.,theywerewidelyusedinindustrialinspection,objectrecognition,workpiecepositioning,robothoming,andmanyotherfields.Inrecentyearsmanyscholarshavedonealotofresearchwork[1-4].Alotofworkwhichfocusedonthemathematicalmodelofvisionmeasurementsystem,thesystemcalibrationmethod[5-7]andthetargetfeaturepointmatchingalgorithm[8-9],whilethestructuralparametersofthesystem(oftwoCCDdistancebetweentheopticalaxisangle,etc.)arerarelystudied.[10]structureparametersofstereoscopicvisioncorrespondingtheoreticalresearch,butitisviewingobjectsfromthestartofthedepthoffeelingbetweentheCCDandtheobjectdistanceandviewingdistanceofthetwoCCDspacingbetween3parameters,didnotaddressthestructuralparametersofthesystemmeasurementaccuracy.Thepracticeprovedthatthestructureofthesystemparametersinpracticalapplicationsofthesystem'smeasurementaccuracyisessential.Inaddition,fromthestereovisionmeasurementprinciple,wecanseetheerrorimagerecognitionsystemaccuracyisanotherimportantfactorinadirectimpact.Basedontheaboveconsiderations,thestructurefromthetheoreticalparametersofthesystemandimagerecognitionerrorsontheprecisionofthesystemofin-depthanalysisandresearch.Combinationofsystemparametersontheaccuracyofthecameracalibrationgivensetofpracticalapplications,stereovisionmeasurementsystemdesign
1Binocularstereovisionmeasurementprincipleandmathematicalmodel
1.1Cameraimagingmodel
Cameraimagingmodel,thegeometricrelationshipbetweentheopticalimagingsystemofmathematicssaid.Atpresenttheapplicationofcameracalibrationarepinholecameraimagingmodelimagingmodel,two-planemodelandartificialneuralnetworkmodel.Inwhichalargenumberofpinholeimagingmodelisusedinanimagingmodel,whichreflectstherelationshipbetweenanideallinearmapshowninFigure1.One,Ocforthecameraopticalcenter,OcXcYcZcforthecameracoordinatesystem,OXYZtheworldcoordinatesystem,oxyforthecameraimagingplanephysicalcoordinates.
P(X,Y,Z)forthespaceofamaterialpoint,p'(x,y)isitsprojectionpointontheimageplane.Accordingtotheimagingmodel,thespaceobjectpointP(X,Y,Z)andtherelationshipbetweentheimagepointcanbeexpressedas
Whentwoormoreintersectioncameras,youcanget2i(i≥2)consistingofequationsoverdeterminedequations,sotheleastsquaresmethodcanbeusedtosolveequationstodeterminethespatialcoordinatesofobjectpoints.
1.2stereovisionmeasurementsystemmodel
BinocularstereovisionsystemusuallyconsistsoftwoidenticalCCDstructureandpropertiesofthecompositionandplacementofthetwoCCDsymmetry.Basedontheabovecameraimagingmodel,from
(2)canintroducethefollowingoverdetermined
Equations:
Wherer,t,r',t'arethetwocameracoordinatesystemrelativetotheworldcoordinatesystemtranslationandrotationmatrix,canbeobtainedthroughcameracalibration.(X,y),(x',y'),respectively,forthespaceobjectpoint(X,Y,Z)inthetwoCCDimageplaneprojectionofthephysicalcoordinates.
Figure2Simplemodelofbinocularstereovision
Inordertoanalyzestructuralparametersofthesystem,wherethebuildingshowninFigure2stereovisionsystem.Inthisstructure,thecoordinatesysteminthesameplane,whichfortheYaxisperpendiculartothepaper,theworldcoordinatesystemOXYZwiththeleftcameracoordinateorigincoincidesOcXcYcZc,twocameraspacingL,theanglebetweenthetwoaxis2α.Accordingtotheabovestructure,thecameracandeterminethecompositionofthetwoequationsfortheoverdetermined
Byequation(4)yields:
2Imagerecognitionerrorsontheaccuracyofthesystem
Stereovisionsystem,thespaceobjectpointintwocameraimageplanepositionisrepresentedbypixelcoordinates,andpixelareaarrayCCDcamerahasacertainphysicalsize,whichmakesthespaceobjectpointintheimageontherealphysicalcoordinatesNottheexactexpression,afundamentalcauseoftheimagerecognitionerrors.
Figure3.
Imageplanepixelcoordinatesandphysicalcoordinatesthefollowingrelations:
Where:
(u,v)theimageinpixelscoordinatesystem,dx,dy,respectively,foreachpixelinthex-axisandyaxisonthephysicalsize,(u0,v0)otheoriginofthecoordinatesystemfortheoxyO0uvcoordinatesysteminthecoordinates[3].ShowninFigure4,assumingthattheimagerecognitionaccuracyof0.5pixel.Foraspaceobjectpoint,settheprojectiontotheimageplaneonthei-line,thefirstjcolumnsofpixels,thenthistimethephysicalcoordinatesofthepoint
x=(i-u0)×dx
y=(j-v0)×dy
Aslongasthepointfallswithinthepixel,thecoordinatevalueisaconstant.Ideally,thecoordinatesofwhichshouldbewithinacertainrange,respectively:
(i-u0-0.5)×dx (j-v0-0.5)×dy Integratedonthetype,thentheerrorshouldpointtoImageRecognition ex=0.5-(x-[x]) ey=0.5-(y-[y]) Where: [x],[y],respectively,forx,yrounded.Sincetheexistenceofimagerecognitionerrors,theactualcoordinatesofimagepointcoordinatesandtheidealimagepointhasthefollowingrelationship: x=? ? X+ex,y=? ? Y+ey,(x,y)asthepointofactualphysicalcoordinates,(? ? x,? ? y)astheidealimagepointofphysicalcoordinates.LetthemeasuredobjectpointcoordinatesP=(^X,^Y,^Z),byequation (1)tocalculatetheprojectionofthepointsinthetwocamerastheidealimagepointcoordinates(? ? X,? ? Y)and(? ? x',? ? y'),considertheimagerecognitionerror,accordingtoequation(8)cometotheactualpixelcoordinates(x,y),(x',y'),besubstitutedinto(4),wehavebeenspacecoordinatesofmeasuringpoint(X,Y,Z),themeasurementerrorofthemeasuredobjectpointcanbeexpressedaseX=X-^X,eY=Y-^Y,eZ=Z-^Z(9) 3Systemparametersanalysisandexperimentalresults 3.1 Structuralparametersoftherelationshipwiththeprecisionofthesystemandmathematicalmodelbasedontheabovederivationprocess,cometothesystemstructureandsystemparametersoftherelationshipbetweenmeasurementerrormap.Figure5isaspecificobjectpointmeasurementerrorandthecameraangle2αbetweenthetwodiagrams.Itcanbeseenfromthefigure,eXvolatilityisnotchanging,eY2αincreaseswiththerisingtrendwasslow,eZismoreviolentchange,withtheincreaseof2αincreasedsignificantly. Figure5Themeasurementerrorisaspecificspatialpointtheanglebetweenthetwoaxisgraph Figure6foracertainobjectpointwithinthecoordinateoriginwiththeworldaveragemeasurementerrorandthetwocamerasandtwocameraangle2αbetweenthedistancebetweentheLmap.Itcanbeseen,whenacertaindistancebetweenthetwocameras,theaverageerrorwiththeincreaseof2α,whentheanglebetweenthetwocamerasisfixed,theaverageerrorincreaseswiththedistanceincreasing. Figure6Averageerrorandtheanglebetweentwoaxes,thedistancebetweenthetwocameraschart Overall,structuralparametersandprecisionofthesystemisamorecomplexfunctioncanbesummarizedasfollows: 1)Spacingbetweenthecameraandthemeasurementerrorisdirectlyproportionaltothesmallerdistance,thesmallertheerror;2)Whenthecameraisnotgreaterthantheanglebetweenthe130°,themeasurementerrorissmall,whereaslarger.Hashighcredibility. 3.2Structuralparametersontheaccuracyofcameracalibration Inpractice,theneedtocreatetwolinksbetweenCCDcoordinates,whichneedtobetwo-dimensionalCCDcalibration,inordertoobtaintherotationbetweenthetwoCCDmatrixandtranslationmatrix.Provedtheprecisionofcameracalibrationparametersandsystemstructurealsohasaverycloserelationship.Calibrationmethodusesatemplatebasedonsingle-planecalibrationstrategy,theaccuracywasassessedusinganassessmentbasedonthelengthofthecheckerboardmethod.Themethodalsocanbeusedasmeasurementerrorofthemeasurementmethod.Calibrationtemplateof10to50mmlengthofthecheckerboardwasrepeatedexperimentalresultsshowninTable1. Table1Structureparametersontheaverageerrorofcalibration. AscanbeseenfromTable1,whenthecameraacertaindistance,thecalibrationerrorincreaseswiththeopticalaxisangleincreasingwhentheanglebetweenthefixedaxis,thecameracalibrationerrorwithincreasingdistanceincreases.Experimentalresultsdemonstratethatwhenthedistancebetweenthetwocamerasisnotmorethan500mm,two-axisangleofnotmorethan60°,thecalibrationerrorissmall. 4Conclusion Integratedsystemparametersonthemeasurementaccuracyandprecisionofcalibration,stereovisionsystemintheestabli
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