Question

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

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

I have both X, Y coordinates for both points and I need to rotate the image X degrees so it looks like this instead:

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

Basically so they align next to eachother, what’s the math for this? (A code example in C# would be even better but not required)

Answer 1

It depends on which point you want to use as a ‘center’ for your rotation. Let’s call the point to the up and left pointA and the one to the right and below pointB. If you want to rotate around the point A so that point B aligns with it, calculating the rotation angle in radians would go like this:

double angle = Math.Atan2(pointB.Y - pointA.Y, pointB.X - pointA.X); 

I don’t how you’re handling your image, so the following applies only if you’re using System.Drawing.Graphics:

myImage.TranslateTransform(-pointA.X, -pointA.Y); myImage.RotateTransform((float) angle, MatrixOrder.Append); myImage.TranslateTransform(pointA.X, pointA.Y, MatrixOrder.Append); 

Hope it helps.