如何使用360度旋转获得正确的2D方向

Question

I'm trying to get the nearest direction for an object to spin too or shortest.

Basically the idea is that the object is given a desired direction and must spin towards that direction the shortest way possible.

I have the following code:

rotationChangeAmount = (this.getDirection(getRotation(), mDestinationRotation)) ? -rotationChangeAmount : rotationChangeAmount;

Using the following function:

private boolean getDirection(double targetRotation, double value)
{
    //Max 100 max (360)
    //Target 60
    //Value 30
    //Value - Max > Target - Max

    if(Math.abs(targetRotation - 360.0) > Math.abs(value - 360.0))
    {
        return false;
    }
    return true;
}

Answer 1

Thinking about this logically, if the distance between the value and the target Rotation is greater than 180, clockwise, if it is less, counter clockwise, assuming target < original.

Say I have 270 initially and I want 180. abs (270-180) is 90, so I will rotate counter clockwise, which we know from a cursory look is correct.

If I have 270 initially and I want 45, then (270-45) = 225, so I would rotate clockwise (which we also know is correct) 135 degrees

If I have 45 initially and I want 300, then abs (45 - 300) = 255, so I would rotate counter clockwise (since initial is less than target) 105 degrees.

Finally, if I have 45 initially and I want 90, then abs (45 - 90) = 45 and I would rotate clockwise 45 degrees.

So, to build your function on this logic:

 private double getChange(double target, double original){
      if (target < original){
           if (Math.abs(original - target) > 180)
               return Math.abs((360 - original) + target);
           else
               return (-1 * Math.abs(target - original);
      }
      else{
           if (Math.abs(target - original) > 180)
               return Math.abs( (360 - target) + original);
           else
               return (-1 * Math.abs(original - target);
      }
 }

Answer 2

Done via TDD:

package rotation;

import static org.junit.Assert.*;
import org.junit.Test;

public class RotationTest {
    public enum Direction { RIGHT, LEFT, EITHER }

    public Direction getDirection(double current, double target) {
        validate(current);
        validate(target);
        double alwaysLarger = current < target ? (current + 360) : current;
        double gap = alwaysLarger - target;
        return gap > 180
            ? Direction.RIGHT
            : (gap == 180 ? Direction.EITHER : Direction.LEFT);
    }

    private void validate(double degrees) {
        if (degrees < 0 || degrees > 360) {
            throw new IllegalStateException();
        }
    }

    @Test
    public void test() {
        assertEquals(Direction.LEFT, getDirection(90, 1));
        assertEquals(Direction.LEFT, getDirection(90, 359));
        assertEquals(Direction.LEFT, getDirection(90, 271));
        assertEquals(Direction.EITHER, getDirection(90, 270));
        assertEquals(Direction.RIGHT, getDirection(90, 269));
        assertEquals(Direction.RIGHT, getDirection(90, 180));
    }
}