Angle between two vectors is defined to be between 0
and 180 only. Angle between 0 an 180 obtained by dot
product is the right answer.
Sanjiva
--- sexyazn5tud <sexyazn5tud@yahoo.com> wrote:
> Hi everyone. I can't seem to figure this out. Can
> someone give me
> some guidance?
>
> Objective: Given two normal vectors, determine the
> angle between them
> from 0 to 360 degrees. The 0 to 360 is IMPORTANT
> because I need to
> know which quadrant it is in.
>
> I have attempted to use the "Dot Product". However,
> this only returns
> a value from 0 to 180. Also, due to the nature of
> cosine, there are
> multiple vectors that can give the same angle. [ie
> (1,0,0) dot
> (1,1,0) and (1,0,0) dot (1,-1,0)]. Both equate to
> 45 degrees.
> However, I can't figure out how to determine if it
> is 45 degrees or 315.
>
> I was thinking I could check to the X & Y values to
> determine their
> sign.
>
> X | Y | QUADRANT
> ----------------
> + | + | I (0 to 90)
> - | + | II (90 to 180)
> - | - | III (180 to 270)
> + | - | IV (270 to 360)
>
> But, what do I do with the Z!?? Since the dot
> product for 3d space is
> x1*x2 + y1*y2 + z1*z2, I cannot ignore the Z values.
> But, I don't
> know how to use it to determine the quadrant/correct
> angle.
>
> Any guidance would be appreciated! Thanks!
>
>
Sanjiva Dayal, B.Tech.(I.I.T. Kanpur)
Address:A-602, Twin Towers, Lakhanpur, Kanpur-208024, INDIA.
Phones:+91-512-2581532,2581426.
Mobile:9415134052
Business email:sanjivadayal@yahoo.com
Personal email:sanjivadayal@hotmail.com
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