Get Rotation of a Group or Object

[conzar]

Is it possible to get the rotation of an object relative to the origin? Simular to the get_centre function.

For example, say you have 2 boxes in a group. You rotate that group on the x-axis by pi. Is there a way that I can get the rotation about the x,y,z axis? So for the example here I should get rotation (3.14,0,0).
If we rotate the group again in the same direction on the same axis by pi again, then we should get [0,0,0].

[Andy]

Sorry, this is not currently possible since the vertices are rotated in the global space.

[conzar]

Ok, I think its possible to do this ... check my math and let me know what u think.

Have a group that is to be copied.
The copies of the group are to be translated and rotated.

I think it is possible to get the rotation of the groups by doing the following:
* translating the copy back to the origin (where the location of the original is)
* calculate the rotation of the x,y,z axis via the location of vertaces.
-> ie, take the first vertex from the copy and the first vertex from the original and
apply the math below




The above math is derived from the information found at the link below.
http://www.tpub.com/math2/5.htm

So what do you think? Does this sound feasible? I need functions that do the following

• translate group to origin
• Get a specific vertex in a group (the first one)
• arc tan function

I know there are functions available in the ac3d headers that do the first 2. So can I use the Math.h functions to get arc tan or is there something available in the headers for that?

(Update) I've answered my own question here - I just tried atan and Math.h works!

[conzar]

Arg. Looks like the math above is flawed b/c one doesn't know in which order the object was rotated.

So I have come up w/ another possible solution. Here it is:

Create a plugin that records the rotations applied to an object as well as which order the rotations were applied. I think this is a simple solution; none-the-less, its a solution.

I'll report back in a few days ...

[conzar]

Hey.
So I can't seem to find a function call to rotate an object.
The only functions I found that seemed close are listed below.

set_global_matrix_rotate(float rx, float ry, float rz)
void rotate_object(ACObject *ob)

What I would like to have is something like

ac_rotate_object(ACObject *ob, float rx, float ry, float rz)

Is there anything like that?

Thanks

[PerFnurt]

Can't you use the 2 function calls in the way you're requesting?

void my_rotate_object(ACObject *ob, float rx, float ry, float rz)
{
set_global_matrix_rotate(rx,ry,rz);
rotate_object(ob);
recordRotationSomehow(rx,ry,rz);
}

[conzar]

Hot dang your right. Just saw your post today ... so I'll try that tonight.

Thanks

[conzar]

Humm. Seems like the above code rotates an object about the origin. How would I rotate it about the center of the object? I would like the same functionality as the rotate buttons on the left side bar.

Thanks.

[Dennis]

Originally Posted by conzar

Humm. Seems like the above code rotates an object about the origin. How would I rotate it about the center of the object? I would like the same functionality as the rotate buttons on the left side bar.

You'll want to move the object to the origin, rotate it, then move it back to its original position. The rotation function exposed through the SDK doesn't handle the translation part of the equation.

Alternatively, you could call the code that AC3D uses when you use the left side bar rotate function. Check out the ac3d.tcl file in the "scripts" directory and look for "ac3d rotate_axis_angle". This snippet might help:

// Specify axis where 0 = x, 1 = y, 2 = z
int axis = 1;
float degrees = 90.0f;
tcl_command( "ac3d rotate_axis_angle %d %g", axis, degrees );

The above code should rotate the selected geometry 90 degrees around the Y axis, relative to the object/selection center. Note that this is off the cuff and untested.

Good luck

[conzar]

Yep. That did the trick.

Thanks!!!!