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The problem is this line here:

float pt_3D_data = (float) pt_3D.data;

pt_3D.data is a pointer to the start of the data your casting this to a float storing it in a float and then trying to use it as a pointer. This is all over the place and I'm surprised it compiles tbh.

It should be:

float *pt_3D_data = pt_3D.data;

The problem is this line here:

float pt_3D_data = (float) pt_3D.data;

pt_3D.data is a pointer to the start of the data your casting this to a float storing it in a float and then trying to use it as a pointer. This is all over the place and I'm surprised it compiles tbh.

It should be:

float *pt_3D_data = pt_3D.data;

The problem is this line here:

float pt_3D_data = (float) pt_3D.data;

pt_3D.data is a pointer to the start of the data your casting this to a float storing it in a float and then trying to use it as a pointer. This is all over the place and I'm surprised it compiles tbh.

It should be:

float *pt_3D_data = pt_3D.data;

EDIT: Okay that's updated now.

I really recommend you use the cv::Mat::at methods to access and update the elements of the cv::Mat object this is exactly what they're for, accessing the data directly and casting pointers all over the place is going to cause you a world of pain.

The data property of the Mat object has a type of uchar* so when you index it with an lvalue using [2] you're adding two bytes to it not (2 * sizeof(float)), you're then casting a non-aligned pointer to a float* which if nothing else if going to give you garbage values. All in all stick to the at methods unless performance is really important to you.