angle between two vectors
in [Matlab]
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From: brian adams on 6 Aug 2010 14:49 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?
From: us on 6 Aug 2010 14:59 "brian adams" <adamsbriand(a)yahoo.com> wrote in message <i3hlf0$olk$1(a)fred.mathworks.com>... > In 2-space, I have a three points: > c, the ctr > p, an arbitrary point, and > v, a point indicating a direction (as a vector from the ctr to v). > > I need to determine whether the point p is in the forward direction of the vector v from the center point, c. > > I have gotten this to work by means of the law of cosines to determine the angle between the the vectors, p-c and v-c. I needed to calculate the distances between the three points, apply acos, and determine if the abs of the angle is <= 90. > > However, this method is computational intensive for the number of points for which I need to perform this operation. > > Is there a less computationally intensive means by which to determine this? show CSSM your ML code that you've come up with so far... us
From: us on 6 Aug 2010 14:59 On Aug 6, 8:51 pm, "brian adams" <adamsbri...(a)yahoo.com> wrote: > In 2-space, I have a three points: > c, the ctr > p, an arbitrary point, and > v, a point indicating a direction (as a vector from the ctr to v). > > I need to determine whether the point p is in the forward direction of the vector v from the center point, c. > > I have gotten this to work by means of the law of cosines to determine the angle between the the vectors, p-c and v-c. I needed to calculate the distances between the three points, apply acos, and determine if the abs of the angle is <= 90. > > However, this method is computational intensive for the number of points for which I need to perform this operation. > > Is there a less computationally intensive means by which to determine this? do NOT double post... us
From: Roger Stafford on 6 Aug 2010 15:18 "brian adams" <adamsbriand(a)yahoo.com> wrote in message <i3hlf0$olk$1(a)fred.mathworks.com>... > 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? - - - - - - - If dot(p-c,v-c) > 0, then p is in the "forward" direction if I interpret you correctly. No need to find the angle or the lengths of the vectors. Roger Stafford
From: brian adams on 6 Aug 2010 16:11 Roger That worked beautifully. Thank you. Brian
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