Another observation in Boids>>isInFieldOfVision: aBoid ... ownDirection := self velocity - self position.
the own direction should be the same as the velocity. Consider a Boid at position 100@0 with velocity 100@0 would give ownDirection = 0@0. But of course, the steering direction is still 1@0. 2014-03-17 10:07 GMT+01:00 Nicolai Hess <nicolaih...@web.de>: > 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. >>> >>> >> >
