四次PythagoreanHodograph速端曲线的构造的综述报告PythagoreanHodographcurves(PHcurves)areafamilyofplanarcurvesthathavebeenwidelystudiedoverthepastfewdecadesduetotheirinterestingandusefulproperties.Inthisreport,wewilldiscusstheconstructionofPHcurvesandfocusonthefourmostwell-knowntypesofPHcurves:theClothoid,EulerSpiral,CornuSpiral,andGeronoLemniscate.PHcurvesarecurveswhosecurvatureandtorsionarebothproportionaltothearclength.Thispropertymakesthesecurvesidealformanyapplications,includingmotionplanning,robotics,andcomputergraphics.Inaddition,PHcurveshaveseveralotherusefulandinterestingproperties,suchastheirabilitytoconnecttwopointswithasmoothtransitioninbothpositionandorientation.TheconstructionofPHcurvesinvolvessolvingasystemofdifferentialequations.Thesystemisderivedfromthefundamentaltheoremofalgebrathatstatesthatapolynomialofdegreenhasnroots.InthecaseofPHcurves,thepolynomialinquestionisthethird-degreepolynomialthatdescribesthecurvatureofthecurve.ThefirsttypeofPHcurvewewilldiscussistheClothoid,alsoknownastheEulerSpiral.Thiscurvehasaconstantrateofchangeofcurvatureandisusedinhighwayengineeringtodesigncurvesthatprovideasmoothtransitionfordrivers.Thecurveisdefinedbythedifferentialequation:y''(s)=k(s)x'(s)wherek(s)isthecurvatureofthecurveatarclengths.Thesolutiontothisequationisgivenby:x(s)=cos(θ(s))y(s)=sin(θ(s))whereθ(s)=1/2∫0^sk(t)dt.ThesecondtypeofPHcurveistheEulerSpiral.Thiscurvehasaconstantrateofchangeofcurvatureandisusedinroboticsandanimationtocreatesmoothmotions.Thecurveisdefinedbythedifferentialequation:y''(s)+k^2(s)y(s)=0wherek(s)isthecurvatureofthecurveatarclengths.Thesolutiontothisequationisgivenby:x(s)=∫0^scos(∫0^tk(τ)dτ)dty(s)=∫0^ssin(∫0^tk(τ)dτ)dtThethirdtypeofPHcurveistheCornuSpiral,alsoknownastheFresnelIntegralCurve.Thiscurveisusedinopticstodescribethediffractionpatterngeneratedbyaslit.Thecurveisdefinedbythedifferentialequation:y''(s)+x''(s)=0wherex(s)andy(s)arethecoordinatesofthecurveatarclengths.ThesolutiontothisequationisgivenbytheFresnelintegrals:x(s)=∫