Calculating aspect ratio of Perspective Transform destination image

Question

I\'ve recently implemented Perspective Transform in OpenCV to my app in Android. Almost everything works without issues but one aspect nee

Answer 1

Thanks to y300 and this post https://stackoverflow.com/a/1222855/8746860 I got it implemented in Java. I'll leave this here in case someone has the same problems I had converting it to Java...

public float getRealAspectRatio(int imageWidth, int imageHeight) {

    double u0 = imageWidth/2;
    double v0 = imageHeight/2;
    double m1x = mTopLeft.x - u0;
    double m1y = mTopLeft.y - v0;
    double m2x = mTopRight.x - u0;
    double m2y = mTopRight.y - v0;
    double m3x = mBottomLeft.x - u0;
    double m3y = mBottomLeft.y - v0;
    double m4x = mBottomRight.x - u0;
    double m4y = mBottomRight.y - v0;

    double k2 = ((m1y - m4y)*m3x - (m1x - m4x)*m3y + m1x*m4y - m1y*m4x) /
            ((m2y - m4y)*m3x - (m2x - m4x)*m3y + m2x*m4y - m2y*m4x) ;

    double k3 = ((m1y - m4y)*m2x - (m1x - m4x)*m2y + m1x*m4y - m1y*m4x) /
            ((m3y - m4y)*m2x - (m3x - m4x)*m2y + m3x*m4y - m3y*m4x) ;

    double f_squared =
            -((k3*m3y - m1y)*(k2*m2y - m1y) + (k3*m3x - m1x)*(k2*m2x - m1x)) /
                    ((k3 - 1)*(k2 - 1)) ;

    double whRatio = Math.sqrt(
            (Math.pow((k2 - 1),2) + Math.pow((k2*m2y - m1y),2)/f_squared + Math.pow((k2*m2x - m1x),2)/f_squared) /
                    (Math.pow((k3 - 1),2) + Math.pow((k3*m3y - m1y),2)/f_squared + Math.pow((k3*m3x - m1x),2)/f_squared)
    ) ;

    if (k2==1 && k3==1 ) {
        whRatio = Math.sqrt(
                (Math.pow((m2y-m1y),2) + Math.pow((m2x-m1x),2)) /
                        (Math.pow((m3y-m1y),2) + Math.pow((m3x-m1x),2)));
    }

    return (float)(whRatio);
}