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Thread Subject:
angle between two vectors

Subject: angle between two vectors

From: brian adams

Date: 6 Aug, 2010 18:51:05

Message: 1 of 2

In 2-space, I have a three points:
c, the ctr
p, an arbitrary point, and
 v, a point indicating a direction (as a vector from the ctr to v).

I need to determine whether the point p is in the forward direction of the vector v from the center point, c.

I have gotten this to work by means of the law of cosines to determine the angle between the the vectors, p-c and v-c. I needed to calculate the distances between the three points, apply acos, and determine if the abs of the angle is <= 90.

However, this method is computational intensive for the number of points for which I need to perform this operation.

Is there a less computationally intensive means by which to determine this?

Subject: angle between two vectors

From: us

Date: 6 Aug, 2010 18:59:50

Message: 2 of 2

On Aug 6, 8:51 pm, "brian adams" <adamsbri...@yahoo.com> wrote:
> In 2-space, I have a three points:
> c,  the ctr
> p, an arbitrary point, and
>  v, a point indicating a direction (as a vector from the ctr to v).  
>
> I need to determine whether the point p is in the forward direction of the vector v from the center point, c.
>
> I have gotten this to work by means of the law of cosines to determine the angle between the the vectors, p-c and v-c.  I needed to calculate the distances between the three points, apply acos, and determine if the abs of the angle is <= 90.
>
> However, this method is computational intensive for the number of points for which I need to perform this operation.
>
> Is there a less computationally intensive means by which to determine this?

do NOT double post...

us

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