How to find angle between two points?

[betazold]

Best explanation ever: mathforum.org/library/drmath/view/61081.html

"I'll call the two points (x1,y1)

and (x2,y2).

  x2 = x1 + cos(a * (pi / 180)) * u
  y2 = y1 + sin(a * (pi / 180)) * u

Subtract the starting point coordinates:

  x2 - x1 = cos(a * (pi / 180)) * u
  y2 - y1 = sin(a * (pi / 180)) * u

Divide the second equation by the first:

  (y2-y1)/(x2-x1) = (sin(a*pi/180)*u)/(cos(a*pi/180)*u)

What is sin/cos? It's the tangent.

  (y2-y1)/(x2-x1) = tan(a*pi/180)

We can find the angle by taking the inverse tangent (arctan) of both 
sides:

  a*pi/180 = arctan((y2-y1)/(x2-x1))

  a = 180/pi * arctan((y2-y1)/(x2-x1))"

@темы: Algorithms