Question

I am trying to rotate a 2D Point in java around another with a specified degree value, in this case simply around Point (0, 0) at 90 degrees.

Method:

public void rotateAround(Point center, double angle) {
    x = center.x + (Math.cos(Math.toRadians(angle)) * (x - center.x) - Math.sin(Math.toRadians(angle)) * (y - center.y));
    y = center.y + (Math.sin(Math.toRadians(angle)) * (x - center.x) + Math.cos(Math.toRadians(angle)) * (y - center.y));
}

Expected for (3, 0): X = 0, Y = -3

Returned for (3, 0): X = 1.8369701987210297E-16, Y = 1.8369701987210297E-16

Expected for (0, -10): X = -10, Y = 0

Returned for (0, -10): X = 10.0, Y = 10.0

Is something wrong with the method itself? I ported the function from (Rotating A Point In 2D In Lua – GPWiki) to Java.

EDIT:

Did some performance tests. I wouldn’t have thought so, but the vector solution won, so I’ll use this one.

Answer 1

If you have access to java.awt, this is just

double[] pt = {x, y};
AffineTransform.getRotateInstance(Math.toRadians(angle), center.x, center.y)
  .transform(pt, 0, pt, 0, 1); // specifying to use this double[] to hold coords
double newX = pt[0];
double newY = pt[1];