Re: [Visualpython-users] obtaining pos in world co-ordinates of a frame obj

[Jonathan B. <jdb...@un...>]

Bruce Sherwood wrote:

> I've added Jonathan's routine to the on-line documentation for "frame" 
> and also updated the Doc zip file that can be downloaded. Thanks, 
> Jonathan.
>
> This does leave open the question however as to whether there ought 
> not be a method in Visual for resolving pos and axis information. In 
> particular, I believe that even Jonathan's routine isn't really 
> complete if this frame is inside another frame: one should really 
> recurse up the enclosing frames.
>
> Bruce Sherwood
>
> Jonathan Brandmeyer wrote:
>
>> Let me amend that routine.  You also have to normalize the y_axis vector
>> (smacks self on head).
>>
>> def world_space_pos( frame, local):
>>     """Returns the position of local in world space."""
>>     x_axis = norm(frame.axis)
>>     z_axis = norm(cross(frame.axis, frame.up))
>>     y_axis = norm(cross(z_axis, x_axis))
>>     return frame.pos + local.x*x_axis + local.y*y_axis + local.z*z_axis
>
Bruce is right: the above function should be named "parent_space_pos" 
instead.
For completeness, here is what the recursive version would look like, in 
the event anyone needs it right now:

def world_space_pos(frame, local):
    x_axis = norm(frame.axis)
    z_axis = norm(cross(frame.axis, frame.up))
    y_axis = norm(cross(z_axis, x_axis))
    parent_space = frame.pos + local.x*x_axis + local.y*y_axis + 
local.z*z_axis
    if (frame.frame == None):
       return parent_space
    else:
       return world_space_pos(frame.frame, parent_space)