Distance from point to line intersection and included angle of line

1、 The distance between a point and a line

        P The straight line AB Distance of .

//P For a little off the line ,AB Two endpoints for the segment 
float getDist_P2L(CvPoint pointP, CvPoint pointA, CvPoint pointB)
{
    // Find the linear equation 
    int A = 0, B = 0, C = 0;
    A = pointA.y - pointB.y;
    B = pointB.x - pointA.x;
    C = pointA.x*pointB.y - pointA.y*pointB.x;
    // Substitute the formula of the distance from the point to the straight line 
    float distance = 0;
    distance = ((float)abs(A*pointP.x + B*pointP.y + C)) / ((float)sqrtf(A*A + B*B));
    return distance;
}

2、 The intersection of lines

         Using point oblique expression to express straight line , Then solve the equations composed of two straight lines .

         Solution ：

x0 = (b2 - b1) / (k1 - k2 + 1e-4) 
y0 = k1 * x0 + b1

3、 The included angle of the straight line

         We know straight lines l1：y=k1x+b1,l2：y=k2x+b2, Find the angle between these two lines .

Conclusion ：

　　l1 To l2 The steering angle of is θ, be tanθ=(k2- k1）/(1+ k1*k2）

　　l1 And l2 An Angle of θ, be tanθ=∣(k2- k1)/(1+ k1*k2)∣

　　 Be careful ： The included angle of two straight lines refers to the angle formed by two straight lines less than 90° Acute angle of , Obviously, in the included angle formula “ horn ” It's not always the angle between two straight lines .