This was of course wrong, I don't know what the other method computes, but not the angle between two vectors.
Now the question is, why do you think your method is wrong / the boids behave wrong? 2014-03-16 18:41 GMT+01:00 Nicolai Hess <nicolaih...@web.de>: > Rounding error? > > This may be the reason, igor's version is working with > cos = (a dot b)^2 / (|ab|^2) > while you are using > cos = (a dot b) / |ab| > > > > > > 2014-03-16 17:01 GMT+01:00 MartinW <w...@fastmail.fm>: > > Hello, >> i probably made some embarassing mistake, but as i cannot find it, i ask >> you >> to have a look at this method. >> It should calculate the angle between two vectors. And vectors are >> instances >> of Point (perhaps here is already a misconception?). >> It is used in my flocking simulation PharoBoids >> (http://smalltalkhub.com/#!/~MartinWalk/Boids) >> >> Here is my version of the method: >> >> angleBetween: vector1 and: vector2 onError: aBlock >> | cosinusOfAngle innerProductOfVectors productOfVectorsLengths| >> innerProductOfVectors := (vector1 dotProduct: vector2). >> productOfVectorsLengths := (vector1 r) * (vector2 r). >> productOfVectorsLengths = 0 ifTrue: [ ^ aBlock value ]. >> cosinusOfAngle := innerProductOfVectors / productOfVectorsLengths. >> ^ cosinusOfAngle arcCos >> >> But my Boids behave wrong when i use it. I found another implementation of >> the same problem by Igor Stasenko which works and looks like this: >> >> angleBetween: p1 and: p2 ifDegenerate: aBlock >> " Calculate an angle (in radians) between two vectors. >> Evaluate a block, in case if calculation not possible because one of the >> vectors has zero length " >> >> | x1 y1 x2 y2 dot2 n2 | >> x1 := p1 x. >> y1 := p1 y. >> x2 := p2 x. >> y2 := p2 y. >> >> dot2 := x1 * x2 + (y1 * y2). >> dot2 := dot2 * dot2. >> >> n2 := (x1*x1 + (y1*y1)) * (x2*x2 + (y2*y2)). >> >> n2 = 0 ifTrue: [ ^ aBlock value ]. >> >> ^ (dot2 / n2) arcCos >> >> Can anybody explain the problem of my method? M. >> >> >> >> -- >> View this message in context: >> http://forum.world.st/Calculate-angle-between-two-vectors-probably-Igor-tp4749351.html >> Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. >> >> >
