Iphone 6 camera calibration for OpenCV

Question

Im developing an iOS Augmented Reality application using OpenCV. I\'m having issues creating the camera projection matrix to allow the OpenGL overlay to map directly on top of t

Answer 1

In my non-OpenCV AR application I am using field of view (FOV) of the iPhone's camera to construct the camera projection matrix. It works alright for displaying the Sun path overlaid on top of the camera view. I don't know how much accuracy you need. It could be that knowing only FOV would not be enough you.

iOS API provides a way to get field of view of the camera. I get it as so:

AVCaptureDevice  * camera = ...
AVCaptureDeviceFormat * format = camera.activeFormat;
float fieldOfView = format.videoFieldOfView;

After getting the FOV I compute the projection matrix:

typedef double mat4f_t[16]; // 4x4 matrix in column major order    

mat4f_t projection;
createProjectionMatrix(projection,
                       GRAD_TO_RAD(fieldOfView),
                       viewSize.width/viewSize.height,
                       5.0f,
                       1000.0f);

where

void createProjectionMatrix(
        mat4f_t mout, 
        float fovy,
        float aspect, 
        float zNear,
        float zFar)
{
    float f = 1.0f / tanf(fovy/2.0f);

    mout[0] = f / aspect;
    mout[1] = 0.0f;
    mout[2] = 0.0f;
    mout[3] = 0.0f;

    mout[4] = 0.0f;
    mout[5] = f;
    mout[6] = 0.0f;
    mout[7] = 0.0f;

    mout[8] = 0.0f;
    mout[9] = 0.0f;
    mout[10] = (zFar+zNear) / (zNear-zFar);
    mout[11] = -1.0f;

    mout[12] = 0.0f;
    mout[13] = 0.0f;
    mout[14] = 2 * zFar * zNear /  (zNear-zFar);
    mout[15] = 0.0f;
}