Unity: Particle System start rotation completely incorrect when set via C# script

Question

I am trying to set the starting rotation of a particle system via c# script so that the particles orientate with another object in the scene. My particle system 3d rotation is set as follows:

void UpdateParticleSystemRotation(Quaternion rotation)
    {
        if(this.gameObject.GetComponent<ParticleSystem>() != null)
        {
            var particleSystemMainModule = gameObject.GetComponent<ParticleSystem>().main;
            particleSystemMainModule.startRotationX = new ParticleSystem.MinMaxCurve(rotation.eulerAngles.x);
            particleSystemMainModule.startRotationY = new ParticleSystem.MinMaxCurve(rotation.eulerAngles.y);
            particleSystemMainModule.startRotationZ = new ParticleSystem.MinMaxCurve(rotation.eulerAngles.z);
        }
        else
        {
            Debug.LogError("There was an error");
        }
    }

The rotation.eulerAngles.x/y/z values are coming through correctly, and by debugging in VS I can see that the values have been correctly assigned, as below:

However I observe that the particle system is not at all orientated with this X value, and the particle system is showing a completely different value:

You can see from the screenshots above that a value of 74.5f becomes 4274.2f by the time it hits the particle system.

I have double checked that the type expected by the ParticleSystem.MinMaxCurve constructor is a float. I cannot understand why this is happening.

I would be very grateful if someone would be able to provide some clarification on this.

Many thanks in advance.

---

I should add, rotation seems completely random for any given input value, it doesn't follow any obvious rhyme or rhythm.

I am using Unity 2017.2.0f3

Answer 1

When in doubt, don't forget to read the docs:

public ParticleSystem.MinMaxCurve startRotationX;

The initial rotation of particles around the X axis when emitted.

Note that the value should be given in radians

So 74.5 radians converted to degrees for display in the editor is:

74.5 • 180° / π = 4268.5°

Which looks on par with what you're seeing in the inspector.

Dropping the scale of all your code-provided angles to a few multiples of π should make things behave much more sensibly.

Also remember that order matters when composing rotations, like the x, y, and z angles in Euler form, so take this into account when planning the angles you use to avoid surprises.