# Rotations

## Rotation

Defines a class that can represent geometric rotations.

`quaternion: Quaternion`

The quaternion that this rotation uses.

`constructor(rotation?: (Quaternion | AxisAndAngle | FromToRotation | LookRotation | QuaternionRotation | SequenceRotation | EulerAnglesRotation)): Rotation`

Creates a new rotation using the given parameters.

The **first parameter** is optional and is a (Quaternion | AxisAndAngle | FromToRotation | LookRotation | QuaternionRotation | SequenceRotation | EulerAnglesRotation) and is the information that should be used to construct the rotation.

#### Examples

`const rotation = new Rotation({`

axis: new Vector3(0, 0, 1),

angle: Math.PI / 2

}); // 90 degree rotation around Z axis

`const rotation = new Rotation({`

from: new Vector3(1, 0, 0),

to: new Vector3(0, 1, 0)

}); // Rotation that rotates (1, 0, 0) to (0, 1, 0)

`const rotation = new Rotation({`

direction: new Vector3(1, 0, 0),

upwards: new Vector3(0, 0, 1),

errorHandling: 'nudge'

});

`tags.homeRotation = new Rotation({`

axis: new Vector3(1, 0, 0),

angle: Math.PI / 6 // 30 degrees

});

`axisAndAngle(): AxisAndAngle`

Gets the axis and angle that this rotation rotates around.

`combineWith(other: Rotation): Rotation`

Combines this rotation with the other rotation and returns a new rotation that represents the combination of the two.

The **first parameter** is a Rotation and is the other rotation.

#### Examples

`const first = new Rotation({`

axis: new Vector3(1, 0, 0),

angle: Math.PI / 4

}); // 45 degree rotation around X axis

const second = new Rotation({

axis: new Vector3(1, 0, 0),

angle: Math.PI / 4

}); // 45 degree rotation around X axis

const third = first.combineWith(second); // 90 degree rotation around X

os.toast(third);

`invert(): Rotation`

Calculates the inverse rotation of this rotation and returns a new rotation with the result.

#### Examples

`const first = new Rotation({`

axis: new Vector3(1, 0, 0),

angle: Math.PI / 4

}); // 45 degree rotation around X axis

const inverse = first.inverse();

const result = first.combineWith(inverse);

os.toast(result);

`rotateVector2(vector: Vector2): Vector3`

Rotates the given `Vector2`

by this quaternion and returns a new vector containing the result.
Note that rotations around any other axis than (0, 0, 1) or (0, 0, -1) can produce results that contain a Z component.

The **first parameter** is a Vector2 and is the 2D vector that should be rotated.

#### Examples

`const rotation = new Rotation({`

axis: new Vector3(1, 0, 0),

angle: Math.PI / 4

}); // 45 degree rotation around X axis

const point = new Vector2(1, 2);

const rotated = rotation.rotateVector2(point);

os.toast(rotated);

`rotateVector3(vector: Vector3): Vector3`

Rotates the given `Vector3`

by this quaternion and returns a new vector containing the result.

The **first parameter** is a Vector3 and is the 3D vector that should be rotated.

#### Examples

`const rotation = new Rotation({`

axis: new Vector3(1, 0, 0),

angle: Math.PI / 4

}); // 45 degree rotation around X axis

const point = new Vector3(1, 2, 0);

const rotated = rotation.rotateVector3(point);

os.toast(rotated);

`toString(): string`

Converts this rotation to a human-readable string representation.

#### Examples

`const myRotation = new Rotation({`

axis: new Vector3(1, 0, 0),

angle: Math.PI / 4

}); // 45 degree rotation around X axis

const rotationString = myRotation.toString();

os.toast('My Rotation: ' + rotationString);

`static interpolate(first: Rotation, second: Rotation, amount: number): Rotation`

Constructs a new rotation that is the spherical linear interpolation between the given first and second rotations. The degree that the result is interpolated is determined by the given amount parameter.

The **first parameter** is a Rotation and is the first rotation.

The **second parameter** is a Rotation and is the second rotation.

The **third parameter** is a number and is the amount that the resulting rotation should be interpolated between the first and second rotations. Values near 0 indicate rotations close to the first and values near 1 indicate rotations close to the second.

`static quaternionFromAxisAndAngle(axisAndAngle: AxisAndAngle): Quaternion`

Constructs a new Quaternion from the given axis and angle.

The **first parameter** is a AxisAndAngle and is the object that contains the axis and angle values.

`static quaternionFromTo(fromToRotation: FromToRotation): Quaternion`

Constructs a new Quaternion from the given from/to rotation. This is equivalent to calculating the cross product and angle between the two vectors and constructing an axis/angle quaternion.

The **first parameter** is a FromToRotation and is the object that contains the from and to values.

`static quaternionLook(look: LookRotation): Quaternion`

Constructs a new Quaternion from the given look rotation.

The **first parameter** is a LookRotation and is the object that contains the look rotation values.

## Quaternion

Defines a class that represents a Quaternion. That is, a representation of a 3D rotation.

Quaternions are a mathematical representation of 3D transformations and are commonly used to calculate and apply rotations to 3D points.
They work by defining a quaterion such that q = w + x*i + y*j + z*k, where w, x, y, and z are real numbers and i, j, and k are imaginary numbers.
The basics of this is that x, y, and z define a vector that represents the rotation axis, and w defines an angle around which the rotation occurs.
However, because i, j, and k are included we can keep x, y, and z from incorrectly interacting with each other and so avoid common pitfalls like Gimbal lock.

One little known feature of quaternions is that they can also represent reflections and also scale. This is because there are two different ways to apply a quaternion to a 3D point:

- quaterion * point * inverse(quaterion)

This formula rotates and scales the point quaternion. The rotation occurs around the axis specified by the quaternion X, Y, and Z values. Additionally, the point will be scaled by the length of the quaternion. (i.e. sqrt( x^2 + y^2 + z^2 + w^2 )) This is why quaternions that are used to represent only rotations must be normalized.

- quaternion * point * quaternion

This formula reflects scales the point by the quaternion. The reflection occurs across the axis specified by the quaternion X, Y, and Z values. Additionally, the point will be scaled by the length of the quaternion. (i.e. sqrt( x^2 + y^2 + z^2 + w^2 ))

`w: number`

The W value of the quaternion.

`x: number`

The X value of the quaternion.

`y: number`

The Y value of the quaternion.

`z: number`

The Z value of the quaternion.

`constructor(x: number, y: number, z: number, w: number): Quaternion`

Creates a new Quaternion with the given values.

The **first parameter** is a number and is the X value.

The **second parameter** is a number and is the Y value.

The **third parameter** is a number and is the Z value.

The **fourth parameter** is a number and is the W value.

`equals(other: Quaternion): boolean`

Determines if this quaternion equals the other quaternion.

The **first parameter** is a Quaternion and is the other quaternion to apply.

`invert(): Quaternion`

Calculates the conjugate of this quaternion and returns the result. The conjugate (or inverse) of a quaternion is similar to negating a number. When you multiply a quaternion by its conjugate, the result is the identity quaternion.

`length(): number`

Gets the length of this vector. That is, the pathagorean theorem applied to X, Y, Z, and W.

`multiply(other: Quaternion): Quaternion`

Multiplies this quaternion by the other quaternion and returns the result. In quaternion math, multiplication can be used to combine quaternions together, however unlike regular multiplication quaternion multiplication is order dependent.

Which frame of reference you want to use depends on which order you use. For example, q2.multiply(q1) starts with the identity, applies q1 to it, and then applies q2 to that. Whereas, q1.multiply(q2) starts with the identity, applies q2 to it, and then applies q1 to that.

The **first parameter** is a Quaternion and is the other quaternion.

`normalize(): Quaternion`

Calculates the normalized version of this quaternion and returns it. A normalized quaternion is a quaternion whose length equals 1.

Normalizing a quaternion preserves its rotation/reflection while making the length (i.e. scale) of it 1.

`squareLength(): number`

Calculates the square length of this quaternion and returns the result. This is equivalent to length^2, but it is faster to calculate than length because it doesn't require calculating a square root.

`toString(): string`

## AxisAndAngle

## FromToRotation

## SequenceRotation

## QuaternionRotation

Defines an interface that represents a rotation constructed from a Quaternion.

`quaternion: object`

## LookRotation

Defines an interface that represents a rotation transforms (0, 1, 0) and (0, 0, 1) to look along the given direction and upwards axes.

`errorHandling: ("error" | "nudge")`

How errors with the direction and upwards vectors should be handled. If the direction and upwards vectors are parallel or perpendicular, then it is not possible to create a rotation that looks along the direction and uses the upwards vector. The upwards vector is essentially useless in this scenario and as a result there are an infinite number of possible valid rotations that look along direction vector.

This parameter provides two ways to handle this situation:

- "error" indicates that an error should be thrown when this situation arises.
- "nudge" indicates that the direction vector should be nudged by a miniscule amount in an arbitrary direction. This causes the upwards and direction vectors to no longer be parallel, but it can also cause rotation bugs when the direction and upwards are the same.

`upwards: Vector3`

The direction that the upward axis should be pointing along after the rotation is applied. If the direction and upwards vectors are not perpendicular, then the direction will be prioritized and the angle between upwards and the resulting upwards vector will be minimized.

If direction and upwards are perpendicular, then applying the rotation to (0, 0, 1) will give the upwards vector.