Math.Atan2产生奇怪的结果？

问题描述

首先，我的数学不强！但我计算某点的角度从原点（0,0）到（1，-1）。

这角度为225°或5π/ 4。

• 在5π/ 4 = 3.9269908169872415480783042290994
• Math.Atan2（-1，-1）= -2.3561944901923448

也许我的 Math.Atan2 的理解是不正确，但我认为这是为了回报给出了一圈，其原产地是两个点的角度（0度， 0）。我认为这里发生的是，从 ATAN2 是翻转的结果，因为它是在X轴的负方...有人可以确认并提供适当的办法做到这一点？

这是我的测试，它失败：

  Assert.AreEqual（（5 * Math.PI）/ 4，Math.Atan2（-1，-1））;
 

这是我的 PointD 类，它包含点X和Y：

 公共双ToRadians（）
{
    双弧度= Math.Atan2（this.Y，this.X）;

    返回弧度;
}
 

解决方案

你的假设是正确的。 ATAN2 给出的结果范围在-pi到+ PI。如果你想要一个数字范围为0到二皮音乐，只是如果加上二皮其结果是小于0

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注意：断言对浮点值相等像这通常不是个好主意......

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*为方便日后参考，这类细节通常是明确的文档中给出​​。例如：http://msdn.microsoft.com/en-us/library/system.math.atan2.aspx.

First, my math is not strong! But I was calculating the angle of a point from the origin (0, 0) to (-1, -1).

This angle is 225° or 5π/4.

• 5π/4 = 3.9269908169872415480783042290994
• Math.Atan2(-1, -1) = -2.3561944901923448

Perhaps my understanding of Math.Atan2 is incorrect but I thought it was meant to return the degree of an angle given two points on a circle whose origin is (0, 0). What I assume is happening here is that the result from Atan2 is "flipped" since it is on the negative side of the X axis...can someone confirm and provide the proper way to do this?

This is my test, which fails:

Assert.AreEqual((5 * Math.PI) / 4, Math.Atan2(-1, -1));

And here's my PointD class which holds points X and Y:

public double ToRadians()
{
    double radians = Math.Atan2(this.Y, this.X);

    return radians;
}

解决方案

Your assumption is correct. Atan2 gives a result in the range -pi to +pi. If you want a number in the range 0 to 2pi, just add 2pi if the result is less than 0.

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Note: Asserting for equality on floating-point values like this is usually not a good idea...

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