Re: [Visualpython-users] frame() (bug or feature?)

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

It's a subtle geometry issue having to do with a discontinuity at the 
scene.up direction. I confess I've never fully wrapped my head around 
the problem. It's more a feature than a bug, in that I don't know a way 
around this within the Visual framework, and it's not getting "fixed" 
even in Visual 5 (about to be released).

Bruce

rsa...@mt... wrote:
> On Windows XP SP3 (Python 2.5.1, VPython 3.2.11), the following use of 
> frame() gives an unexpected flip in the y- and z-axes in some of the 
> frames.
> 
> By uncommenting the line:
> if costh<0: Fup=-Fup
> I get the desired behavior.
> 
> Is this a bug?
> 
> Rob Salgado
> 
> 
> # example of frame()
> 
> from visual import *
> 
> scene.background=(.5,.5,.5)
> scene.forward=(0,20,-10)
> 
> DEG=math.pi/180.
> F=[]
> 
> for th in arange(0,360*DEG, 30*DEG):
>    costh=cos(th)
>    sinth=sin(th)
> 
>    Fup=scene.up
>    #if costh<0:    Fup=-Fup
> 
>    F.append(frame(pos=6*norm( vector(costh, sinth, 0) ), 
> axis=vector(costh,sinth,0) , up=Fup))
> 
>    arrow(frame=F[-1],color=color.red,   axis=vector(1,0,0) )
>    arrow(frame=F[-1],color=color.green, axis=vector(0,1,0) )
>    arrow(frame=F[-1],color=color.blue,  axis=vector(0,0,1) )
>    label(frame=F[-1],text="%3d" % round(th/DEG) ,box=0, opacity=0)
> 
> 
> 
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