Re: [Plib-users] Problem with rotations

[Ben W. <za...@ec...>]

Ok, I see what you are talking about and it makes sence. But why would this
only cause a problem with pitch. I know that is questionable to return back
from a matrix, so I tried it just using the matrix and not returning it back
and got the same results..

Ben
----- Original Message -----
From: "Steve Baker" <sjb...@ai...>
To: <pli...@li...>
Sent: Tuesday, September 10, 2002 1:47 AM
Subject: Re: [Plib-users] Problem with rotations


>
>
> Ben Woodhead wrote:
>
> > Ya, I don't have a problem with that.. It seems to be sgMakeRotMat(mat,
> > h,p,r) where pitch is set to something other then 0. Then I converted it
> > back to sgCoord and used transform...
>
> Could your confusion be this:
>
>     * You take three angles (H,P,R) and convert them into a matrix M
>       (using sgMakeRotMat...or whatever).
>
>     * Then you convert M *BACK* into an sgCoord and extract (H',P',R').
>
> Do you expect (or rely upon) H' == H,  P' == P and R' == R ???
>
> If so, then that's not right.  There are an infinite number of values
> for H,P,R that all generate the exact same rotation matrix.  Hence, when
> you convert a matrix *BACK* into three Euler angles, you don't get the
> same three angles back...although the three angles you get *DO* perform
> the same effective rotation as the three you put in.
>
> Hence, it's possible to say things like:
>
>      H =   0
>      P = 180
>      R =   0
>
> ...then convert to a matrix...convert back again and get back:
>
>      H' = 180
>      P' =   0
>      R' = 180
>
> ...totally different numbers - but having the same exact same effect.
>
> If that is your problem, then it's not something that we can fix - it's
> just the way math works.
>
> ----------------------------- Steve Baker -------------------------------
> Mail : <sjb...@ai...>   WorkMail: <sj...@li...>
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>
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