What is the angle of vector conecting two points?

Suppose I have two points P1(x1,y1) and P2(x2,y2). How can I calculate angle of vector connecting the two points?

[TastyPastry]

The angle of the vector and what? The x or y axis?

[K M Ibrahim Khalilullah]

no, for pixels of an image. It is related to the direction...

Answer 1

[KSSV]

Angle means, it shall be anti-clockwise with respect to x -axis... use: theta = atan((y2-y1)/(x2-x1))

[K M Ibrahim Khalilullah]

thanks for reply>>Actually I need directional vector of the line connecting two point.