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Re: Calculate the included angle between two vectors [message #65971]

Fri, 10 April 2009 02:47

jameskuyper
Messages: 79
Registered: October 2007

Member

Chris wrote:
> On Apr 9, 5:43 am, Pierre <pierre.villene...@gmail.com> wrote:
>> On Apr 9, 7:14 am, "dux...@gmail.com" <dux...@gmail.com> wrote:
>>
>>> Is there a function which can calculate the included angle between
>>> two three-dimensional vectors?
>>> jdu
>> Here's a simple solution. Assume v1 and V2 are each three-element
>> vectors of any magnitude. Compute the angle in degrees as follows:
>>
>> angle = acos( transpose(v1)#v2 / sqrt(total(v1^2)) / sqrt(total
>> (v2^2)) ) * 180./!pi
>>
>> Good luck.
>
> There is an issue with this method due to the fact that acos cannot
> distinguish between positive and negative angles (cos(-theta) = cos
> (theta)).

The angle between two vectors is by definition positive; the question
asked does not provide enough information to assign a sign to the angle.
"Enough information" could be, for instance, a third vector which
defines (via the right-hand rule) which direction of rotation counts as
a clockwise rotation, and which one is counterclockwise.

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[Message index]

		Re: Calculate the included angle between two vectors By: jameskuyper on Fri, 10 April 2009 02:47
		Re: Calculate the included angle between two vectors By: duxiyu@gmail.com on Fri, 10 April 2009 02:15
		Re: Calculate the included angle between two vectors By: Chris[6] on Thu, 09 April 2009 10:41
		Re: Calculate the included angle between two vectors By: Pierre V. on Thu, 09 April 2009 08:43

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