Oolite JavaScript Reference: Quaternion - Revision history

Norby: link to Quaternion calculator

2014-06-20T10:05:00Z

link to Quaternion calculator

2013-01-14T18:19:49Z

‎Constructor: note bug

2013-01-10T23:14:23Z

‎Quaternions for Rotations

2013-01-10T23:10:12Z

‎rotate

2013-01-10T23:09:20Z

‎rotateZ

2013-01-10T23:08:56Z

‎rotateY

2013-01-10T23:08:30Z

‎rotateX

2012-12-26T22:00:46Z

‎Quaternion Expressions: Removed obsolete musings.

2012-12-24T10:51:53Z

‎conjugate: Incorrect synopsis.

2012-11-23T18:08:06Z

‎Methods: Conjugate

← Older revision		Revision as of 10:05, 20 June 2014
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	Rotations can be combined by quaternion multiplication (see the <code>[[#multiply\|multiply]]()</code> method). Note that quaternion multiplication is not commutative; that is, ''PQ'' is not the same as ''QP''. If this seems strange, take a box or book and assign it ''x'', ''y'' and ''z'' axes. Rotate it about the ''x'' axis and then the ''y'' axis. Then, rotate it about the ''y'' axis followed by the ''x'' axis. If the results of the two rotations are the same, you’re doing it wrong.		Rotations can be combined by quaternion multiplication (see the <code>[[#multiply\|multiply]]()</code> method). Note that quaternion multiplication is not commutative; that is, ''PQ'' is not the same as ''QP''. If this seems strange, take a box or book and assign it ''x'', ''y'' and ''z'' axes. Rotate it about the ''x'' axis and then the ''y'' axis. Then, rotate it about the ''y'' axis followed by the ''x'' axis. If the results of the two rotations are the same, you’re doing it wrong.
		+
		+	The [https://app.box.com/s/6usw7ozbvobze3hkouzc Quaternion calculator] is a very useful spreadsheet to get quaternions from rotation angles.

	=== Quaternion Expressions ===		=== Quaternion Expressions ===

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 === Constructor ===
  '''new Quaternion'''([value : [[#Quaternion Expressions|quaternionExpression]]])
-Create a new quaternion with the specified value. If no value is provided, the vector is initialized to the identity quaternion (1, 0, 0, 0).
+Create a new quaternion with the specified value. If no value is provided, the quaternion is initialized to the identity quaternion (1, 0, 0, 0).
 === <code>conjugate</code> ===

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 Additionally, a rotation quaternion must be normalized; that is, it must fulfill the '''normal invariant''' ''Q<sub>w</sub>''² + ''Q<sub>x</sub>''² + ''Q<sub>y</sub>''² + ''Q<sub>z</sub>''² = 1. Unlike with [[property list]] scripting and specifications, quaternions will not be automatically normalized for you except where specified, but a <code>[[#normalize|normalize]]()</code> method is provided.
-An '''identity rotation''' – that is, one which, when applied, has no effect – is represented by the '''identity quaternion''' (1, 0, 0, 0).
+An '''identity rotation''' – that is, one which, when applied, has no effect – is represented by the '''identity quaternion''' (1, 0, 0, 0). Often you will want to start with this identity quaternion before applying the methods '''rotate''', '''rotateX''', '''rotateY''' or '''rotateZ'''.
 The <code>Quaternion</code> class provides several methods to make construction of rotations easier: <code>[[#rotate|rotate]]()</code>, <code>[[#rotateX|rotateX]]()</code>, <code>[[#rotateY|rotateY]]()</code>, <code>[[#rotateZ|rotateZ]]()</code>.

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 === <code>rotate</code> ===
  function '''rotate'''(a : [[Oolite JavaScript Reference: Vector#Vector Expressions|vectorExpression]], angle : Number) : Quaternion
-Returns a quaternion rotated <code>angle</code> radians about the axis of <code>a</code>. The vector <code>a</code> must be a normalized vector. (FIXME: clockwise or anticlockwise?)
+Returns a quaternion rotated <code>angle</code> radians about the axis of <code>a</code>. The vector <code>a</code> must be a normalized vector. A positive angle is anti-clockwise if the vector is pointing towards you.
 === <code>rotateX</code> ===

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 === <code>rotateZ</code> ===
  function '''rotateZ'''(angle : Number) : Quaternion
-Returns a quaternion rotated <code>angle</code> radians about the ''z'' axis. (FIXME: clockwise or anticlockwise?)
+Returns a quaternion rotated <code>angle</code> radians about the ''z'' axis. A positive angle is anti-clockwise if the ''z'' axis is pointing towards you.
 <code>q.rotateZ(angle)</code> is equivalent to <code>q.[[#rotate|rotate]]([0, 0, 1], angle)</code>.

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 === <code>rotateY</code> ===
  function '''rotateY'''(angle : Number) : Quaternion
-Returns a quaternion rotated <code>angle</code> radians about the ''y'' axis. (FIXME: clockwise or anticlockwise?)
+Returns a quaternion rotated <code>angle</code> radians about the ''y'' axis. A positive angle is anti-clockwise if the ''y'' axis is pointing towards you.
 <code>q.rotateY(angle)</code> is equivalent to <code>q.[[#rotate|rotate]]([0, 1, 0], angle)</code>.

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 === <code>rotateX</code> ===
  function '''rotateX'''(angle : Number) : Quaternion
-Returns a quaternion rotated <code>angle</code> radians about the ''x'' axis. (FIXME: clockwise or anticlockwise?)
+Returns a quaternion rotated <code>angle</code> radians about the ''x'' axis. A positive angle is anti-clockwise if the ''x'' axis is pointing towards you.
 <code>q.rotateX(angle)</code> is equivalent to <code>q.[[#rotate|rotate]]([1, 0, 0], angle)</code>.

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 === Quaternion Expressions ===
-All Oolite-provided functions which take a quaternion as an argument may instead be passed an [[Oolite JavaScript Reference: Entity|Entity]] instead, in which case the entity’s <code>[[Oolite JavaScript Reference: Entity#orientation|orientation]]</code> is used. In specifications, this is represented by arguments named <code>quaternionOrEntity</code>. (Is this actually useful? It seems less compellingly so than the [[Oolite JavaScript Reference: Vector#Vector Expressions|vector equivalent]]. -- [[User:Ahruman]])
+All Oolite-provided functions which take a quaternion as an argument may instead be passed an array of four numbers, or an [[Oolite JavaScript Reference: Entity|Entity]] (in which case the entity’s <code>[[Oolite JavaScript Reference: Entity#orientation|orientation]]</code> is used). In specifications, this is represented by arguments typed <code>quaternionExpression</code>.
 == Properties ==

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 === <code>conjugate</code> ===
 {{oolite-method-added|1.77}}
- function '''conjugate'''(q : [[#Quaternion Expressions|quaternionExpression]]) : Quaternion
+ function '''conjugate'''() : Quaternion
 Return the conjugate of the quaternion (i.e. the quaternion which when multiplied by the original quaternion returns the identity quaternion). The input quaternion must be normalized.