[英]Move points in the opposite direction
I am working on a project in Java. 我正在用Java开发一个项目。 I am trying to move the points
p2
, p3
, p4
just outside the circumference of the circle in the opposite direction to the point p1. 我试图将点
p2
, p3
, p4
沿与点p1相反的方向移动到圆的圆周之外。 Below is the image, which describes the problem, I am trying to solve. 下图是描述我要解决的问题的图像。
//given two points, calculates the angle
public static double calcAngle(Point2D.Double p1, Point2D.Double p2) {
double deltaX = p2.x - p1.x;
double deltaY = p2.y - p1.y;
return (Math.atan2(deltaY, deltaX) * 180 / Math.PI);
}
//calculates a point on a circle given the angle, center of the circle and the radius
public static Point2D.Double pointOnCircle(Point2D.Double point, double radius , double angle) {
double x = Math.abs(point.x + (radius * Math.cos(angle * Math.PI / 180F)));
double y = Math.abs(point.y + (radius * Math.sin(angle * Math.PI / 180F)));
return new Point2D.Double(x,y);
}
How do I calculate the angle in Java coordinate system and destination co-ordinates for each of the points p2
, p3
, p4
? 如何在Java坐标系和目标坐标中为每个点
p2
, p3
, p4
计算角度?
I am yet to try the code above and would like to know if my approach is right before proceeding, since it is a part of the bigger project. 我尚未尝试上面的代码,并且想知道我的方法在继续之前是否正确,因为它是较大项目的一部分。 Thanks in advance!
提前致谢!
Your general idea seems workable but overly complicated. 您的总体思路似乎可行,但过于复杂。 There is no need to convert from x/y-vector to angle and then back.
无需先将x / y矢量转换为角度再转换为角度。 SImply scaling vectors will be enough.
简单地缩放向量就足够了。
Point2D p = p2; // likewise for p3, p4
double factor = radius / p.distance(p1);
p.setLocation(p1.getX() + (p.getX() - p1.getX())*factor,
p1.getY() + (p.getY() - p1.getY())*factor);
This takes the vector (p - p1)
, ie the vector pointing from p1
towards p
, scales it by factor
and adds it to the position of p1
. 这将采用向量
(p - p1)
,即从p1
指向p
的向量,按factor
对其进行缩放并将其添加到p1
的位置。 The factor
is chosen such that the new distance is equal to radius
. 选择该
factor
,以使新距离等于radius
。
All of this will fail if p1
and p
are the same, since in this case you'll have a division by zero. 如果
p1
和p
相同,所有这些将失败,因为在这种情况下,您将被零除。 If this can be a problem for you, you might want to ensure that factor
is a finite number, eg using Double.isFinite(double)
. 如果这对您来说可能是个问题,则可能需要确保
factor
是有限的,例如使用Double.isFinite(double)
。
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