An Improved Flexible Camera Calibration Technique for Rock Three Dimensional Shape Measurement System

摘要

Withtheseadvantagessuchasnophaseshifterror,measuredfast,portable,highaccuracy,thethree-dimensionalmeasurementsystemwhichisbasedontheheterodyneprincipleanddigitalgratingphase-shifttechnologyhasbeenwidelyusedinrockthree-dimensionalshapemeasurement.Theprecisionofcameracalibrationdeterminesthemeasurementaccuracyofthesystem.Inthispaper,theZhangZhengyouplanarflexiblecalibrationmethodisimprovedandanimprovedflexiblecameracalibrationmeansispresented.Thismethodadoptsalensdistortionmodelbasedonsecond-orderradialdistortionandsecond-ordertangentialdistortionandusesahighprecisionplanarcalibrationtargetprintedwithcirculartargets.First,gettingtheinitialvaluesofcameramodelthroughimagepointsnearthecenter,theinitialvaluescanbeagoodapproximationoftheexactvaluesbecausethedistortionofthesepointsnearthecenterissmall.Then,usingtheentirecalibrationboardimages,allparameterscanbeacquiredbyapplyingmaximumlikelihoodestimation.TheexperimentalresultsshowthatthisapproachissuperiortoZhang’sinprecisionandrobustness.