4、)ontheionosphericdelayofpositioningaccuracy.Wecandrawapositiveconclusionthatinthearea at latitudemorethan57.5°,KlobucharmodeladoptedbyGPShave a negative effectin most cases,butbetterthanBDS.Nequickmodelperformsworsethanmiddleandlowlatitudes,itscorrectioneffectismos