Method angle

src/frameworks/UBGeometryUtils.cpp:423–441

* @brief Return the angle in degrees between three points */

 * @brief Return the angle in degrees between three points
 */
qreal UBGeometryUtils::angle(const QPointF& p1, const QPointF& p2, const QPointF& p3)
{
    // Angle between three points, using the law of cosines:
    // The angle at B equals arccos((a^2-b^2+c^2)/(2*a*c)), where a, b and c are the sides of the triangle
    // opposite A, B and C, respectively

    qreal a, b, c, beta;
    a = qSqrt(qPow(p2.x() - p3.x(), 2) + qPow(p2.y() - p3.y(), 2));
    b = qSqrt(qPow(p1.x() - p3.x(), 2) + qPow(p1.y() - p3.y(), 2));
    c = qSqrt(qPow(p1.x() - p2.x(), 2) + qPow(p1.y() - p2.y(), 2));

    if (a == 0 || c == 0)
        beta = 3.14159;
    else
        beta = qAcos(std::max(-1.0, std::min(1.0, (a*a - b*b + c*c)/(2*a*c))));


    return 180.* beta/3.14159;
}