Getting the right position in Unity - opencv

Question

In OpenCV, there is a rectangle shown when something is detected.
Imgproc.rectangle (rgbaMat, new Point (rects [i].x, rects [i].y), new Point (rects [i].x + rects [i].width, rects [i].y + rects [i].height), new Scalar (0, 0, 255, 255), 2);
I want to put a 3D object or example a cube in that one corner of the rectangle.
myCube.transform.position = new Vector3(rects[0].x, rects[0].y);
The problem is that the position of the cube isnt in the rectangle but in the transform it shows the correct Vector3(float, float, float).
How can I put my cube in the position where the corner of the rectangle is?

Answer 1

I was having a similar problem. I wanted to place a 3d object in the center of the detected object. I asked on the OpenCV for unity forum and got a reply from the developer.
They provide a package with a solution that worked for me. Overlay a 3D object
In your case, you can change line 68 in DetectFace2DTo3DExample.cs to the positions of your rect.
Matrix4x4 point3DMatrix4x4 = Get2DTo3DMatrix4x4 (new Vector2 (rects [0].x, rects [0].y), gameObject);

Answer 2

After digging a lot (so I don't blame you) I've found the following which I think is what you where looking for in this forum:
There is an OpenCv Object detection example.
The for you most interesting method I guess would be the most bottom one:
/// <summary>
/// Results the rects to result game objects.
/// </summary>
/// <param name="rects">Rects.</param>
/// <param name="color">Color.</param>
/// <param name="zPos">Z position.</param>
private void ResultRectsToResultGameObjects (IList<object> rects, Color color, float zPos)
{
Vector3[] resultPoints = new Vector3[rects.Count];
float textureWidth = GetComponent<Renderer> ().material.mainTexture.width;
float textureHeight = GetComponent<Renderer> ().material.mainTexture.height;
Matrix4x4 transCenterM = Matrix4x4.TRS (new Vector3 (-textureWidth / 2, -textureHeight / 2, 0), Quaternion.identity, new Vector3 (1, 1, 1));
Vector3 translation = new Vector3 (gameObject.transform.localPosition.x, gameObject.transform.localPosition.y, gameObject.transform.localPosition.z);
Quaternion rotation = Quaternion.Euler (gameObject.transform.localEulerAngles.x, gameObject.transform.localEulerAngles.y, gameObject.transform.localEulerAngles.z);
Vector3 scale = new Vector3 (gameObject.transform.localScale.x / textureWidth, gameObject.transform.localScale.y / textureHeight, 1);
Matrix4x4 trans2Dto3DM = Matrix4x4.TRS (translation, rotation, scale);
for (int i = 0; i < resultPoints.Length; i++)
{
IDictionary rect = (IDictionary)rects [i];
//get center of rect.
resultPoints [i] = new Vector3 ((long)rect ["x"] + (long)rect ["width"] / 2, (long)rect ["y"] + (long)rect ["height"] / 2, 0);
//translate origin to center.
resultPoints [i] = transCenterM.MultiplyPoint3x4 (resultPoints [i]);
//transform from 2D to 3D
resultPoints [i] = trans2Dto3DM.MultiplyPoint3x4 (resultPoints [i]);
//Add resultGameObject.
GameObject result = Instantiate (resultPrefab, resultPoints [i], Quaternion.identity) as GameObject;
result.transform.parent = gameObject.transform;
result.transform.localPosition = new Vector3 (result.transform.localPosition.x, result.transform.localPosition.y, zPos);
result.transform.localEulerAngles = new Vector3 (0, 0, 0);
result.transform.localScale = new Vector3 ((long)rect ["width"] / textureWidth, (long)rect ["height"] / textureHeight, 20);
result.GetComponent<Renderer> ().material.color = color;
resultGameObjects.Add (result);
}
}
Ofcourse I didn't test that but it looks like it does what you want: place objects on the rects positions.
And ofcourse you will have to adopt it to your needs but I hope it is a good starting point for you.