# Rotation around negative y axis

I want to compute a rotation around the negative y-axis. I am aware that a rotation around the y-axis can be expressed in the following way (angle value is known):

```
tf.transformations.quaternion_axis(
tf.transformations.quaternion_about_euler(0.0, angle, 0.0))
```

But how can I transform this rotation appropriately such that it describes a rotation around the negative y-axis?

HI,

I'm not sure what you mean with "negative y-axis" but when you perform a rotation around an axis is around a defined direction, without considering its sign.

If you can give an example of what are you willing to do, I can help you

Hi ! What I mean is this: if I want a rotation around the y axis (pitch angle) then it is pretty straightforward. I rotate around the [0 1 0] axis. Now, what I want to do is perform a rotation around the [0 -1 0] axis. This is what I am asking.

Basically, It's the same thing: when you rotates around the y axis you're rotating your system around a direction, not around a direction + sign, ok? It doesn't matter if it is the positive or the negative one

Well, doesnâ€™t it matter regarding the positive or negative rotation ? A positive rotation around y axis should be a negative around minus y, right ?