estimateRigidTransform returns an empty matrix

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Hey all,

I'm trying to use estimateRigidTransform in my program to find the best transformation matrix between two point sets using only translation, rotation & uniform scaling.

My two point sets are of type

MatOfPoint2f mPointSetA;
MatOfPoint2f mPointSetB;

and are both of size 20. (They do have 20 rows) For those who wonder, I get them like this:

LinkedList<Point> listOfPointsA;
// fill list with points...

mPointSetA.fromList(ListOfPointsA);

Now I'm calling:

Mat R = Video.estimateRigidTransform(mPointSetA, mPointSetB, false);

But the R that I get is of size 0x0! Could anybody tell me what I'm missing here?

Thanks in advance for any help! Isa