Java:点旋转结果不准确 [英] Java: Point rotation results are not accurate
问题描述
我有以下代码...
public class Point {
private double x;
private double y;
static private final double RADTODEG = 180.0d / Math.PI ;
static private final double DEGTORAD = Math.PI / 180.0d;
/**
* Rotates the point by a specific number of radians about a specific origin point.
* @param origin The origin point about which to rotate the point
* @param degrees The number of radians to rotate the point
*/
public void rotateByRadians(Point origin, double radians) {
double cosVal = Math.cos(radians);
double sinVal = Math.sin(radians);
double ox = x - origin.x;
double oy = y - origin.y;
x = origin.x + ox * cosVal - oy * sinVal;
y = origin.y + ox * sinVal + oy * cosVal;
}
/**
* Rotates the point by a specific number of degrees about a specific origin point.
* @param origin The origin point about which to rotate the point
* @param degrees The number of degrees to rotate the point
*/
public void rotateByDegrees(Point origin, double degrees) {
rotateByRadians(origin, degrees * DEGTORAD);
}
/**
* Rotates the point by the specified number of radians about the axis' origin (0,0). To rotate about a specific origin point, see rotateByRadians(Point, double)
* @param radians Measure of radians to rotate the point
*/
public void rotateByRadians(double radians) {
if(isEmpty()) // Since we're rotating about 0,0, if the point is 0,0, don't do anything
return;
double cosVal = Math.cos(radians);
double sinVal = Math.sin(radians);
double newx = x * cosVal - y * sinVal;
double newy = x * sinVal + y * cosVal;
x = newx;
y = newy;
}
/**
* Rotates the point by the specified number of degrees about to the axis' origin (0,0). To rotate about a specific origin point, see rotateByDegrees(Point, double)
* @param degrees Measure of degrees to rotate the point
*/
public void rotateByDegrees(double degrees) {
rotateByRadians(degrees * DEGTORAD);
}
给定一个点,例如0,200,就会出现问题.将旋转角度(绕轴原点0,0旋转)180度应为(0,-200). x
坐标不应更改.但是,它最终是(-2.4492935982947064E-14,-200).我尝试使用strictfp
,但没有任何区别.仅当旋转的坐标为零时,这才影响结果.非零值可以正常工作.知道为什么这不正确吗?
The problem arises when given a point, say 0,200. Calling the rotation (about axis origin 0,0) for 180 degrees it should be (0, -200). The x
coordinate shouldn't have changed. However, it ends up being (-2.4492935982947064E-14, -200). I tried using strictfp
but it doesn't make a difference. This only affects the result if the coordinate being rotated is zero. Nonzero values work fine. Any ideas why this is not accurate?
代码如下:
Point p = new Point(0.0d, 200.0d);
p.rotateByDegrees(180.0d);
System.out.println(p);
给出输出:
shapelib.Point Object {x: -2.4492935982947064E-14 y: -200.0}
推荐答案
浮点运算不完全准确.在大多数情况下,10 ^ -14幂的误差就足够了.
如果您计算Math.sin(Math.PI)
,您将得到1.2246467991473532E-16
.为什么您的情况下需要精确地得到0?
Float arithmetic is not fully accurate. Error of 10^-14 power is enough in most cases.
If you calculate Math.sin(Math.PI)
you'll get 1.2246467991473532E-16
. Why do you need to get precisely 0 in your case?
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