How do I cast Point2f to Point2d?

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Thanks: I will give that a try just to check what's going on. Treating the vector as a Mat worked for me, I wasn't able to answer my own question though.

 cv::Mat(vector1).convertTo(vector2, cv::Mat(vector2).type())

Why would you want to do this? This is a giant overhead of parsing each vector into a new mat format? ...

Just checked: your version does work! Agreed: the Mat way is terribly inefficient. Still not sure why considering the whole Point2f doesn't work but casting individual elements works.

It is possible that casting for OpenCV specific types is not enabled ... @LBerger, you did nothing special or extra to get that to work? Should dig deeper in this.

My results : [10, 0; 5, 1; 3.333333333333334, 2] [10, 0; 5, 1; 3.3333333, 2] [10, 0; 5, 1; 3.3333333, 2]

with this program so

    vector<Point2d> vd;
    vector<Point2f> vf;
    for (int i=0;i<3;i++)
        vd.push_back(Point2d(10.0/(i+1),i));
    for (int i = 0; i < vd.size(); i++)
    {
        Point2f p=vd[i];
        vf.push_back(vd[i]);
    }
       cout<<vd<<"\n";
       cout<<vf<<"\n";
std::vector<cv::Point2f> vector2(vd.begin(), vd.end());
cout << vector2 << "\n";

May be I miss something (VS2013 windows 10 64bits)

Oh thats implicit type conversion, by forcing one type into the other. That is different than explicit typecasting like he suggested, which does not work --> (cv::Point2d)vector1[i])

I have made this test too and it's OK

for (int i = 0; i < vd.size(); i++)
{
    Point2f p=vd[i];
    vf.push_back((cv::Point2f)vd[i]);
}

in debug mode I can see this call opencv2\core\types.hpp line 1089 and for this test too :

for (int i = 0; i < vd.size(); i++)
{
    Point2f p=vd[i];
    vf.push_back(vd[i]);
}

That only works because you have the line Point2f p=vd[i];. Basically OpenCV uses smart pointers and there you redefine the pointer interface to the item in question. Then ofcourse the pushing will work. Could you test if

for (int i = 0; i < vd.size(); i++)
{
    vf.push_back((Point2f)vd[i]);
}

works. I am guessing it does not.

My test is now

vector<Point2d> vd;
vector<Point2f> vf;
for (int i=0;i<3;i++)
    vd.push_back(Point2d(10.0/(i+1),i));
for (int i = 0; i < vd.size(); i++)
{
    vf.push_back(vd[i]);
}
cout<<"vd ="<<vd<<"\n";
cout<<"vf = "<<vf<<"\n";
std::vector<cv::Point2f> vector2(vd.begin(), vd.end());
cout <<"vector 2="<< vector2 << "\n";

Results :

vd =[10, 0;
 5, 1;
 3.333333333333334, 2]
vf = [10, 0;
 5, 1;
 3.3333333, 2]
vector 2=[10, 0;
 5, 1;
 3.3333333, 2]