Autodesk ObjectARX

[#1]

I can't find any good method to insert a point on a spline, please see the code below.  I want to insert a point on an existing spline, and after insertion ,the shape of the spline shoud not change much. 

AcDbObjectId idSpline;
        if (!Acad_Selection:elEnt(idSpline,_T("spline")))
        {
            return;
        }
        AcDbSplinePointer pSpline(idSpline,AcDb::kForWrite);
        if (Acad::eOk != pSpline.openStatus()) return;

        ads_point pt;
        if (acedGetPoint(NULL,_T("\nclick:"),pt) != RTNORM)
        {
            return;
        }

        AcGePoint3d pt3d;
        pSpline->getClosestPointTo(asPnt3d(pt),pt3d);
        double dParam = -1;
        pSpline->getParamAtPoint(pt3d,dParam);// here , the value of dParam is not what I want.
        
        acutPrintf(_T("\n%g,round:%d,floor:%d,ceil:%d"),dParam,int(dParam+0.5),floor(dParam),ceil(dParam));

        pSpline->insertFitPointAt(floor(dParam),pt3d);

[#2]

What is your overall goal, and what exactly is the problem with the code you posted?

[#3]

my purpose is to insert a fit point to the spline. I get get closest point P1 on the spline for the point I click on the screen.

but  through the method getParamatPoint, the param I got of P1 has nothing to do with the fit point. I want to use insertFitPointAt. and insertFitPointAt requires the number of fit point.  is there an existing method that can return which two fit points P1 is between.

[#4]

There is no existing method to do that directly. You did not describe your overall goal, so I can't offer any alternative solutions.

[#5]

oh, if so , I have to calculate the "param" for each fit point, then compare these params with the insert point and determine which fit point is the right one for "insertFitPointAt".

still,thanks a lot.