Talk:Rotation
Fixed a few minor syntax errors and reworked the top of the article a bit. As an article it is quite far along though it still has a ways to go. Strife Onizuka 03:32, 29 January 2007 (PST)
Intro is awful
"gymbal lock" is something that affects mechanical systems with gyroscopes. A quaternion rotation is a mathematical abstraction. The term simply does not apply, and only serves to confuse things. The reference to "SLERP" without a link is useless. Doran Zemlja
- Gimbal lock effects Euler angles to which you wrote an article using them everywhere without mention it; it is a gross oversight. That sentence is a bit complex on review and yes there is no SLERP article but that doesn't mean someone won't write one (it is better to leave open links then no links; no links give no hint that a page should be created). I may write a short one tomorrow, I already have a function that implements it (I've just been pressed for time). I will find a better article on gimbal lock, the wikipedia one is pretty poor in this regard as it fails to go into the programing implications. I gave you the benefit of the doubt and looked up 'gymbal' in the dictionary, to which it was nowhere to be found; but 'gimbal' was. Strife Onizuka 19:33, 31 January 2007 (PST)
- Gimbal lock affects you every time you use Euler Coordinates, it is not restricted to gyroscopes. German article on wikipedia about gimbal lock shows it much more clearly than the English version -- Catherine Pfeffer 2007-12-08
I'm a mathematician, and think the following text is also misleading (or partially incorrect) in the Other Representations section: "Another way to represent a rotation is using three numbers, <X, Y, Z>, which represent the amount (in radians) which the object is rotated around each axis. This is used in the Edit window..." Technically, 1 "radian" equals the angle that is traced out by an arc along a circle's circumference, when that arc equals the circle's radius. This means that 2*pi radians equals 360 degrees, 1*pi radians equals 180 degrees, and pi/2 radians equals 90 degrees. SL's prim-editing window displays rotations in degrees (360, 180, 90...) and NOT in radians (2pi, pi, pi/2)! However, it IS true that radians must be used when editing values in some LSL script commands! Times Sands 18:18, 10 November 2008 (UTC)
Mirroring using quaternions
I think I have worked out how to mirror a point (and therefore an entire object in pieces,) using quaternions, but does anyone here know how to, or if it is even possible to, define a rotation that turns a left hand into a right hand or vise-versa? This is a three diminsional mirror operation, but in four diminsions it is a simple rotation. (I could be wrong, but based on my research into quaternions it seems right...)
Cron Stardust 22:16, 25 March 2007 (PDT)
- It depends entirely upon which axis you want to mirror around. Save yourself some work and look up Jeffrey's Prim Mirror. Strife Onizuka 11:13, 26 March 2007 (PDT)
Moving this page
Shouldn't the content of this page be moved to Category:LSL Rotation? It seems confusing to me to have multiple Rotation pages.
- Good point, I see no problem merging them. -- Strife Onizuka 08:40, 22 July 2007 (PDT)
- Very true. Or even better, do a "pure maths" one and a "pure lsl" one -- Catherine Pfeffer, 2007-12-08
GetRot()/SetRot() chart
llGetLocalRot() and llGetRot() clearly do *not* return the same value in the root prim of an attachment. While I believe that llGetRot() returns the avatar rotation as indicated, llGetLocalRot() I believe gives the rotation of the root prim relative to the attachment point (or the avatar?)
- You are correct, that entry in the table is wrong. -- Strife Onizuka 08:40, 22 July 2007 (PDT)
Visual aids
I use this page as a visual reference and cheat sheet for quaternion operations. --Tateru Nino 15:53, 9 September 2007 (PDT)
Maths versus LSL
Has anyone noticed that maths' quaternion multiplication is written in reverse order than in LSL ? That is, what you write Q1 . Q2 in maths is computed in LSL with Q2 * Q1. Is that a bug or simply a documentation issue ? -- Catherine Pfeffer - 2007-12-08
- It appears to be a bug, with an obvious patch in the server code, but this bug won't be fixed, so I decided to document the problem here -- Catherine Pfeffer - 2008-08-28
Unjustified preference for Euler notation
One thing that really annoys me with this page is that it seems to consider that the Euler coordinates are the easy way to deal with rotations, while the <x, y, z, s> quaternion representation is almost unintelligible.
That's a common opinon, and as a matter of facts, most LSL scripts I have found use and overuse llEuler2Rot() and llRot2Euler().
But that's simply wrong. Euler's notation is completly unintuitive for any non-trivial situation.
To get convinced of it, try to figure out the Euler angles for the rotation of 45 degrees around XY diagonal (X = Y and Z = 0). Good luck ! :-). Now try figuring out the quaternions's values with the directing vector and sine and cosine of the half-angle: that's straightforward.
I think this page is misleading a lot of new scripters into the wrong direction because of its preference for Euler angles. -- Catherine Pfeffer - 2008-08-28
Rotating Vectors
The example:-
//-- same as: llSetPrimitiveParams( [PRIM_POSITION, llGetPos() + (gPosOffset - gPosOffset * gRotArc) * llGetRot(),PRIM_ROTATION, gRotArc * llGetRot()] );
gives no derivation of the variables gPosOffset and gRotArc. Which is less than useful to someone learning from the text. Gregory McLeod 08:51, 1 September 2008 (PDT)
Useful snippets
The snippet we have now is kind of a string function. How about converting these from XSI to LSL?
How about these from lslwiki.net? ("All functions on this page are released into public domain and may have been based off other public domain works.")
By the way, someone above complained about an unlinked reference to slerp() which seems to now be completely missing(!) Both of those have slerp(). Gia May 07:15, 8 December 2008 (UTC)
- I offer L$5000 to the first person who translates two functions from http://www.isner.com/tutorials/quatSpells/quaternion_spells_12.htm to the Useful snippets here, or for code constraining rotations to an arbitrary conic section. Runners up, if any, will be awarded on merit, and I am also asking the Lindens to help with this library deficiency bug bounty. IM me inworld for details. JS Uralia 21:17, 2 February 2009 (UTC)
- Hello, I went ahead and added three such functions: ConstrainQuaternion2Plane, ScaleQuaternion and CombineQuaternions (Slerp) though this last one already existed on the Wiki.--Jesrad Seraph 07:05, 17 May 2009 (UTC)