Rotate image math (C#)

Question

I have an image with two points, aligned something like this:

|----------------|
|                |
|    .           |
|                |
|          .     |
         


        

Answer 1

First find the centre point:

Point p = new Point((x1-x2)/2, (y1-y2)/2)

Then use trigonomentry to solve for the angle. I'm going to assume we have rebased the origin to our central point so I now have a new x3 and y3 to one of the points.

hypotenuse = SqrRt(x3^2 + y3^2)

We are solving for the unknown angle TH

Sin(TH) = opposite / hypotenuse

So to solve for TH we need:

TH = Asin(y3 / hypotenuse)

Rotate by TH.

See Wikipedia for trigonometric functions reference