图示：延长曲线

代码：正值延长负值缩短

      var cl = workPart.Features.CreateCurvelengthBuilder(null);
      cl.CurvelengthData.ExtensionMethod = NXOpen.GeometricUtilities.ExtensionMethod.Incremental;
      cl.CurvelengthData.ExtensionSide = NXOpen.GeometricUtilities.ExtensionSide.StartEnd;
      cl.CurvelengthData.ExtensionDirection = NXOpen.GeometricUtilities.ExtensionDirection.Natural;
      //修改公差会报警
      //cl.DistanceTolerance = 0.01;
      NXOpen.Section section = workPart.Sections.CreateSection(0.00095, 0.001, 0.01);
      section.SetAllowedEntityTypes(NXOpen.Section.AllowTypes.OnlyCurves);
      section.AllowSelfIntersection(true);
      cl.Section = section;


      NXOpen.IBaseCurve[] curves = curve.ToArrayBySingle();
      NXOpen.CurveDumbRule curveDumbRule = workPart.ScRuleFactory.CreateRuleBaseCurveDumb(curves);
      NXOpen.SelectionIntentRule[] rules = curveDumbRule.ToArrayBySingle();
      NXOpen.Point3d helpPoint = position;
      section.AddToSection(rules, curve, null, null, helpPoint, NXOpen.Section.Mode.Create, false);

      cl.CurvelengthData.SetStartDistance("0");
      cl.CurvelengthData.SetEndDistance("0");
      cl.CurvelengthData.SetStartDistance($"{startLength}");
      cl.CurvelengthData.SetEndDistance($"{endLength}");

      var nxObject = cl.Commit();