Bugzilla – Bug 61
The description for angular velocity
Last modified: 2009-04-09 21:54:50 PDT
under instance_rigid_body section 5-16
Specifies the initial angular velocity of the rigid_body
instance around each axis, in the form of an x-y-z Euler
rotation. The measurement is in degrees per second
This is Wrong.
- It looks like you are trying to describe a velocity as a spin about the x axis and a spin about the y and a spin about the z. That isn't the convention, nor does it make sense. Its a spin, not an orientation.
- should be radians, not degrees.
- Instead of saying seconds, technically it
should be per "unit of time" instead of "per second".
Unless another time scale is being used. (minor point)
fix: Use the following paragraph:
Specifies the initial angular velocity of the rigid_body.
This 3D vector is the axis of rotation with a length equal to the rate of rotation in radians per unit time (typically seconds). Naturally, the direction of spin follows the handedness of the coordinate system.
* the unit of time is seconds.
* the unit of angle is degrees.
Stan, can you provide a clarification within those constraints?
It should be as Stan mentions:
Axis of rotation, with the length of the axis as angular velocity, in radians/second. That is the universally accepted way of representing this info.
No physics engine represents the _length_ of this axis in degrees, this is impossible. We can't start multiplying angular velocity vector by PI/180, it just doesn't make sense.
Note that there is no separate 'angle', it is the length of the vector.
After doing some more research into the conventions used elsewhere in collada and into the unit standards that are specified, it has become clear to me that it is ok to assume seconds is the standard unit of time. So any of my prevoius suggestoins to use "unit of time" instead of "seconds" are not needed. Continue to just use "seconds".
In this case use a sentence such as:
The length of the angular velocity vector is equal to the rate of spin (in radians per second).
in the .doc file that I was editing and sent to Ellen, I had rewritten the appropriate paragraph where it describes angular velocity:
A 3D floating point vector that specifies the initial spin or angular velocity of the rigid_body instance. This vector is also known as the axis of rotation with a magnitude equal to the rate of rotation in radians per second. The direction of spin follows the handedness of the coordinate system. For example, in a right handed system, a spin vector pointed toward the viewer would correspond to an object that is spinning counter-clockwise from the viewer’s perspective.
Fixed in 1.5.0 specification.
Verified in published 1.5.0 spec.