   Finding position of a rotating particle at time t
  I''m wondering if I have a 3D body with constant angular velocity vector, if an expression can be found for the position of a point relative to the centre of the body with just time as the input?For an object spinning about a fixed axis this is easy as in some plane the points just travel in a circle. But with yaw, pitch and roll it''s hard to visualise.Any thoughts?  
  You said your angular velocity vector was constant... Therefore the object will always be spinning about a fixed axis :xSo i''m not quite understanding your question. But given the original position of the point relative to the body and the time that has elapsed, yes you can find out its current position (as long as ur angular velocity vector is constant as u said it would be). ;quote:Original post by SpaceDude   You said your angular velocity vector was constant... Therefore the object will always be spinning about a fixed axis :xNope. The constant angular velocity is not necessarily in an ordinal plane.@d000hg:In linear computation, distance (s) is computed from constant velocity (v) ass = s0 + v*t    In angular terms, substitute your angular velocity (ω ) for v in a single plane.In curvilinear computation (cylindrical coordinates r, θ, φ ), your velocity must also be cylindrical. Consult an elementary dynamics (or physics) text for more information, or try Mathworld.[Edit: Grr! We need to fix the forum smiley parser.]   [edited by - Oluseyi on February 12, 2004 1:01:52 PM];  I suppose it does have an axis then - I mean the quaternion I apply each frame doesn''t change. So I get the axis it''s rotating about and build a plane from it. I can decide that the point is at an angle of 0 with the x-axis in this plane and now get my coordinates with reference to the plane x/y coords with simple circular motion. Cool! ;quote:Original post by Oluseyi  quote:Original post by SpaceDude    You said your angular velocity vector was constant... Therefore the object will always be spinning about a fixed axis :xNope. The constant angular velocity is not necessarily in an ordinal plane.Constant angular velocity means that the angular velocity vector does not change. The axis of rotation is the same as the angular velocity vector. Therefore the axis of rotation does not change either! What part of that do you not understand? 