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

[Jonathan B. <jbr...@ea...>]

On Sun, 2004-03-14 at 17:13, Jonathan Brandmeyer wrote:
> On Sun, 2004-03-14 at 15:52, Axawire wrote:
> > hi
> > 
> > i have created a few frame objects and moved them about in the scene and
> > rotated them. if i select an object in a frame how do i get its pos in world
> > co-ordinates (co-ordinates of the whole scene)?
> > 
> > thanks
> > 
> 
> Simple case: the orientation of the frame has not changed (ie, up points
> along +y and axis points along +x)  simply add the object's pos to the
> frame's pos.
> 
> Harder case: the orientation of the frame is different.  In this case
> you will need to calculate the unit vectors representing the axes of the
> frames local coordinate system, and calculate the object's displacement
> along those unit vectors.
> 
> # Requirements:
> # frame has the following attributes: vector pos, vector axis, vector up
> #    (met by all primitive objects in Visual).
> # local has the following attributes: double x, double y, double z.
> #    (met by vectors and primitive objects in Visual).
> # frame.axis and frame.up are not colinear. (undefined coordinate 
> #    system)
> 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 = cross(z_axis, x_axis))
>     return frame.pos + local.x*x_axis + local.y*y_axis + local.z*z_axis
> 

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

-Jonathan Brandmeyer