Re: [Visualpython-users] Why diff_angle calculates only to pi ?

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

I'm not sure I've understood the issues, but two comments that may be 
relevant:

1) There is a math routine (imported by Visual) that returns angles 
between 0 and 2*pi: atan2(y,x).

2) In the documentation for frame there is a routine for converting from 
a position in a frame to world coordinates.

Bruce Sherwood

Stef Mientki wrote:
> hello,
> 
> playing a few days with vpython,
> I'm very satisfied, it's really powerful.
> But I've the idea,
> I'm missing a few convenience procedures (or at least they are hidden).
> 
> When animating our normal 3D world,
> we always have a floor,
> as a beginner I've the the xz-plane.
> 
> Now when moving objects with the mouse around in this environment,
> I found out that the best thing todo is to project the mouse position on 
> the floor.
> Ok there is a method for, so perfect.
> But I also want other vectors to be projected onto the floor,
> so I made a small ( 1 line ;-) routine for that.
> After moving that routine to a general library,
> I discovered that there's also a "proj" routine inside visual.
> So apparently there might be some interesting hidden routines ?
> 
> Back to the angle difference,
> for my case: mouse position and all objects projected to the floor,
> you can unambiguous determine an angle between 0 and 2*pi.
> This makes life so much easier.
> So why isn't there a procedure for calculating such a difference angle ?
> Or am I doing something stupid by projecting everything on the floor ?
> Or does nobody uses these kind mouse interactions ?
> Or ...?
> Anyway here is the small method
> 
> def XZ_Angle ( axis ) :
>   """projects the vector on the XZ-plane and
>   calculates the angle with the X-axis [ 0 .. 2*pi ]"""
>   axis = vector ( axis.x, 0, axis.z )
>   a1 = axis.diff_angle ( X_AXIS )
>   a2 = axis.diff_angle ( Z_AXIS )
>   if a2 < pi/2 :
>     a1 = 2*pi - a1
>   return a1
> 
> Although trivial, a procedure that translates radians into degrees is 
> very handy in debugging.
> And of course the frame to world translation would be a good candidate 
> for the convenience library.
> 
> Just some thoughts of a beginner,
> 
> cheers,
> Stef Mientki
> 
> 
> 
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