How to rotate an image based on two points

Question

I have some images I manipulate, and in these images I always have two points (x1, y1) and (x2, y2). like this:

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

I need to code an algorythm to align the image like this

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

I already read this question but the angle obtained by

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

Is not working when I use this rotation code in java:

public static BufferedImage tilt(BufferedImage image, double angle) {
    double sin = Math.abs(Math.sin(angle)), cos = Math.abs(Math.cos(angle));
    int w = image.getWidth(), h = image.getHeight();
    int neww = (int) Math.floor(w * cos + h * sin), newh = (int) Math
            .floor(h * cos + w * sin);
    GraphicsConfiguration gc = getDefaultConfiguration();
    BufferedImage result = gc.createCompatibleImage(neww, newh,
            Transparency.OPAQUE);
    Graphics2D g = result.createGraphics();

    g.setColor(Color.white);
    g.setBackground(Color.white);
    g.fillRect(0, 0, neww, newh);

    g.translate((neww - w) / 2, (newh - h) / 2);

    g.rotate(angle, w / 2, h / 2);
    g.drawRenderedImage(image, null);
    g.dispose();
    return result;
}

In the post mentioned before they use the c# code like

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

Is there anybody that could help with a java implementation for this case?

When you say not working, what exactly is going on. I use the exact same code (forgot where it came from) which much success. — user489041, Apr 07 '11 at 14:39
I mean, the rotation does not align the image correctly. One of my images needs a rotation of 19 degrees but the Math.Atan2(pointB.Y - pointA.Y, pointB.X - pointA.X); returns somehting like 2 — Ademir Constantino, Apr 07 '11 at 14:52

score 1 · Accepted Answer · answered Apr 12 '11 at 23:11

1

Ok... to solve the problem I just converted the radians value returned by Math.atan2 to degrees and the rotation worked well.

Thanx everybody

answered Apr 12 '11 at 23:11

Ademir Constantino

171
10

score 0 · Answer 2 · answered May 28 '13 at 06:40

0

for me the below worked to align OMR sheet markings where pointA is TopLeft Corner mark, pointB is BottomLeft corner mark

double angle = Math.Atan2(pointB.x - pointA.x, pointB.y - pointA.y);

answered May 28 '13 at 06:40

Venkat

1

score 0 · Answer 3 · answered Apr 07 '11 at 14:45

0

If the left point in your example is A, and the right point in your example is B, imagine drawing a point C (A.X, B.Y) that has a 90 degree angle to complete the triangle. IF you use geometry calculation to calculate the angle of corner A, you know by how much to rotate.

answered Apr 07 '11 at 14:45

NKCSS

2,716
1
22
38

Sorry but, how can I calculate the corner? – Ademir Constantino Apr 11 '11 at 21:02

How to rotate an image based on two points

3 Answers3