Re: Unit vector -> (h,p,r) ?

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Ran Yakir (rany++at++sgi.com)
Tue, 3 Sep 1996 21:46:54 +0000

> This question probably has a very obvious answer, but for
> some reason it is eluding me:
>
> What is a good reliable way to transform a unit vector (x,y,z) representing
> a direction back into (h,p,r) form? I can sort of do this by doing
>
> h = pfArcTan2(x,y);
> p = pfArcTan2(z,y);
> r = ???;
>
> but this only seems to give the correct results in some cases. (And
> I don't believe there is a way to reconstruct r!)

roll can not be reconstructed from a single vector. A unit vector is
represented with h,p and the length (which is 1). If you need to reconstruct
the roll of an aircraft or a vehicle, and you have the line-of-sight vector,
you'll need the up vector too.
Anyway, to get heading and pitch from (x,y,z) you should do the following :

h = pfArcTan2(x,y);
p = pfArcSin(z);

Hope this helps

Ran

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