# [Interest] Plane rotations

Mike Chinander chinander at gmail.com
Wed Apr 5 15:00:28 CEST 2017

```The following is equivalent to your equation:

float cosAngle = QVector3D::dotProduct(v1.normalized(), v2.normalized());

Your numerator is the dot product and the denominator does the
normalization (makes them unit vectors).

On Wed, Apr 5, 2017 at 7:50 AM, Igor Mironchik <igor.mironchik at gmail.com>
wrote:

> Hi,
>
>
> 05.04.2017 15:13, Sean Harmer пишет:
>
>> Yes, just use the dot product.
>>
>
> You want to say, that QVector3D::dotProduct() will give me an angle?
>
>
>> Sean
>>
>> On Wednesday 05 April 2017 14:59:48 Igor Mironchik wrote:
>>
>>> Hi,
>>>
>>> I Googled it and found:
>>>
>>> The cos of angle between vectors is:
>>> |(ax*bx + ay*by + az*bz)
>>>
>>> -------------------------------------------------------- sqrt(ax*ax +
>>> ay*ay + az*az) * sqrt(bx*bx + by*by + bz*bz)|
>>>
>>> 05.04.2017 14:52, Igor Mironchik пишет:
>>>
>>>> 05.04.2017 14:45, Igor Mironchik пишет:
>>>>
>>>>> Hi,
>>>>>
>>>>> 05.04.2017 14:29, Paolo Angelelli пишет:
>>>>>
>>>>>> Just cross N and M to get the vector around which to rotate.
>>>>>>
>>>>>> Then use a QQuaternion to set the rotation in the
>>>>>> Qt3DCore::QTransform,
>>>>>> and construct it with fromAxisAndAngle(const QVector3D &axis, float
>>>>>> angle)
>>>>>>
>>>>> Ok, I can rotate around the right axis. But what angle should I rotate?
>>>>>
>>>> This is my question.
>>>>
>>>> And how can I calculate new normal to the rotated plane?
>>>>>
>>>> I already know it...
>>>>
>>>> I just need to know what angle should I rotate.
>>>>
>>>> On Wed, 5 Apr 2017 14:18:56 +0300
>>>>>>
>>>>>> Igor Mironchik <igor.mironchik at gmail.com> wrote:
>>>>>>
>>>>>>> Hello,
>>>>>>>
>>>>>>> Let's say I have two vectors - N (normal vector to plane P1) and M
>>>>>>> (normal vector to plane P2).
>>>>>>>
>>>>>>> How to calculate x, y, z axis rotations angles for plane P2 to make
>>>>>>> plane P2 parallel to P1?
>>>>>>>
>>>>>>> How to calculate x, y, z axis rotations angles for plane P2 to
>>>>>>> rotate it
>>>>>>> around vector N?
>>>>>>>
>>>>>>> Thank you.
>>>>>>>
>>>>>>> And what is the measurement of angle in rotationX() of
>>>>>>> Qt3DCore::QTransform?
>>>>>>>
>>>>>>> I need to calculate angles in this units.
>>>>>>>
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>>>>>
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