GetAngle is a math code snippet to calculate the angle between two coordinats. All it needs is the distance between these two coordinats. The resulting angle will be in the range [0.0, 2.0 * pi], these angles ordered like a clock:


12 o'clock is 0.0 * pi

 3 o'clock is 0.5 * pi

 6 o'clock is 1.0 * pi

 9 o'clock is 1.5 * pi


#include <cassert>

#include <cmath>



//From www.richelbilderbeek.nl/CppGetAngle.htm

double GetAngle(const double dX, const double dY)

{

  //In which quadrant are we?

  if (dX > 0.0)

  {

    if (dY > 0.0)

    {

      //dX > 0.0 && dY > 0.0

      //Quadrant IV

      assert(dX > 0.0 && dY > 0.0);

      const double angle = (1.0 * M_PI) - std::atan(dX / dY);

      assert(angle > 0.5 * M_PI && angle < 1.0 * M_PI);

      return angle;

    }

    else if (dY < 0.0)

    {

      //dX > 0.0 && dY <= 0.0

      //Quadrant I

      assert(dX > 0.0 && dY < 0.0);

      const double angle = (0.0 * M_PI) - std::atan(dX / dY);

      assert(angle > 0.0 * M_PI && angle < 0.5 * M_PI);

      return angle;

    }

    else

    {

      //dX > 0.0 && dY == 0.0

      //On Y-axis, right side

      assert(dX > 0.0 && dY == 0.0);

      const double angle = 0.5 * M_PI;

      return angle;

    }

  }

  else if (dX < 0.0)

  {

    if (dY > 0.0)

    {

      //dX < 0.0 && dY > 0.0

      //Quadrant III

      assert(dX < 0.0 && dY > 0.0);

      const double angle = (1.0 * M_PI) - std::atan(dX / dY);

      assert(angle > 1.0 * M_PI && angle < 1.5 * M_PI);

      return angle;

    }

    else if (dY < 0.0)

    {

      //dX < 0.0 && dY < 0.0

      //Quadrant II

      assert(dX < 0.0 && dY < 0.0);

      const double angle = (2.0 * M_PI) - std::atan(dX / dY);

      assert(angle > 1.5 * M_PI && angle < 2.0 * M_PI);

      return angle;

    }

    else

    {

      //dX < 0.0 && dY == 0.0

      //On X-axis

      assert(dX < 0.0 && dY == 0.0);

      const double angle = 1.5 * M_PI;

      return angle;

    }

  }

  else

  {

    if (dY > 0.0)

    {

      //dX == 0 && dY > 0.0)

      //On Y-axis, right side of origin

      assert(dX==0.0 && dY > 0.0);

      const double angle = 1.0 * M_PI;

      return angle;

    }

    else if (dY < 0.0)

    {

      //dX == 0 && dY < 0.0)

      //On Y-axis, left side of origin

      assert(dX==0.0 && dY < 0.0);

      const double angle = 0.0 * M_PI;

      return angle;

    }

    else

    {

      //dX == 0.0 && dY == 0.0)

      //On origin

      assert(dX==0.0 && dY == 0.0);

      const double angle = 0.0 * M_PI;

      return angle;

    }

  }

}

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(C++) GetAngle