# Re: Custom auto rotation

```Hi Bill,

Hibbard wrote:
```
```Hi Ugo,

```
```First we need a bit of maths background to understand my problem.

I have a 3D display which originally is in the default position. Imagine
a vector (u,v,w) which is perpendicular to the xy-plane - that is, is
also parallel to the display's own z-axis. Now, I rotate the display and
this vector changes (with respect to the original vector, which I'm
calling (x,y,z)).
```
```
...

```
```/*
where everything is zero, except rotZ = 1.0 and scale = 1.0
This is what rotates the display; when in a loop -> auto rotation:
*/
display.getProjectionControl()
.setMatrix(display.multiply_matrix(mult, matrix));
```
```

Try reversing the order of the multiply:

display.getProjectionControl()
.setMatrix(display.multiply_matrix(matrix, mult));

That should move the Z-axis rotation to a different
coordinate system.

If that doesn't solve the problem, please let us know
what it does.
```
```
Hmm, how shall I explain what it does?

It does E.X.A.C.T.L.Y. what I wanted!

Thanks a lot!

Ugo
PS.: the original code was in Test57
```
```
Cheers,
Bill

```
```The result of this is rotation around the original z-axis and not the
display's z (called here the w axis).

What I first need to do, is to use the projection matrix to apply a
transformation from (x,y,z) to (u,v,w)

(Proj.Matrix (3 x 3)) X (0,0,1) = (new rotation vector) = (x',y',z')

and then use x',y' and z' in my mult matrix above. Isn't that right?

if (true){

Is there a way to do this in VisAD? (I mean, without using JAMA.)
Has anyone done that?

}else
What am I doing wrong? (I mean, apart from programming gimmicks to
impress the public, rather than doing all the work pilling up on my desk ;-)

```
```