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. > >
