Three-dimensionelectronicchartdisplayinformationsystem(ECDIS)isoneofthenewdevelopingdirectionsofelectronicnavigationchart,anditsreal-timequalityisoneoftheimportantrequirements.Inthispaperthealgorithmofsimplifyingtrianglesurfaceusingedgecontraction,whichcanensurethereal-timedisplayofobjectsinseabedenvironment,wasputforward.TheoptimumcontractionpointwasdeterminedbytheLagrangematrix,sothatthealgorithmensuresthatthecontractionpointlocatesontheoriginalmodel,meanwhilemeetsthedemandsofleastdeviation.Thisalgorithmcanimprovetheplottingspeed,andpreservetheboundarycharacterbyusingthefewertrianglestosimulateobjects.
