Re: [Visualpython-users] Right, so I made this dinky spaceship...

[Bruce S. <Bru...@nc...>]

I think there's a typo in the definition of +y. It should be

+x = object.axis.norm()
+z = object.axis.cross( object.up).norm()
+y = -x.cross( +z) (implicitly orthonormal to x and z)

Bruce Sherwood

Jonathan Brandmeyer wrote:

>On Thu, 2005-12-22 at 22:38 -0500, Jeremy Sachs wrote:
>  
>
>>Hi again. I'm very confused by the methods you can use to rotate an
>>object, specifically a frame.
>>    
>>
>
>Hopefully this explanation will help.
>
>VPython uses 2 vectors to specify the orientation of its objects: axis
>and up.  The coordinate system of the local reference frame (for any
>object, including frame objects) is defined such that
>
>+x = object.axis.norm()
>+z = object.axis.cross( object.up).norm()
>+y = +x.cross( +z) (implicitly orthonormal to x and z)
>
>Another way to say this, is that +y is always coplanar to axis and up,
>orthogonal to axis, such that +y.diff_angle( up ) <= 90 (in degrees)
>
>  
>
>>I made this model spaceship that I want to animate, such that the ship
>>is always pointed in the direction that it's moving. The objects that
>>make up the ship are grouped together in a frame, so that
>>repositioning and rotating the model is a simpler process. The idea is
>>to derive all the necessary information from one vector, called
>>"dndt", that represents the velocity of the ship. That way, if I want
>>to edit the path of the ship, the code that rotates the ship won't
>>break. I've fiddled with the "axis" property of the frame object, and
>>have just gotten really confused. 
>>
>>
>>My program is a big mess, so I made a smaller example file, which is
>>at http://homepage.mac.com/rezmason/spaceship.py . It's very basic,
>>and you can use it however you wish.
>>
>>
>>Thanks,
>>-JS
>>    
>>
>
>
>
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