crossproduct


    Sep 27 2007 | 9:45 am
    Just a quick question to all the mathbuffs out there...
    I want to get the crossproduct of 2 vectors, and for this I set up 2
    matrices going into jit.expr with the following expression :
    expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])" "(in[1].p[3]*in
    [2].p[1])-(in[1].p[1]-in[2].p[3])" "(in[1].p[1]*in[2].p[2])-(in[1].p
    [2]*in[1].p[3])"
    I was wondering if this is correct, and maybe if there's a much more
    simple expression or object for this...?
    grtz.
    Brecht Debackere
    www.autofasurer.net
    M+32(0)498319302
    F+32(0)70429559
    Skype : Bdebackere
    brecht@visualantics.net

    • Sep 27 2007 | 10:56 am
      Hi Brecht,
      I'm not sure but maybe a shader can help. Parts of the shaders derivatives
      are don with matrix calculations.
      It's only an idea. Maybe a bit more complicated. But matrices calculations
      are much faster on gpu than on cpu.
      grr.
      Ranja
      2007/9/27, Brecht Debackere :
      >
      > Just a quick question to all the mathbuffs out there...
      > I want to get the crossproduct of 2 vectors, and for this I set up 2
      > matrices going into jit.expr with the following expression :
      >
      > expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])"
      > "(in[1].p[3]*in[2].p[1])-(in[1].p[1]-in[2].p[3])"
      > "(in[1].p[1]*in[2].p[2])-(in[1].p[2]*in[1].p[3])"
      >
      > I was wondering if this is correct, and maybe if there's a much more
      > simple expression or object for this...?
      >
      > grtz.
      > Brecht Debackere
      >
      > www.autofasurer.net
      > M+32(0)498319302
      > F+32(0)70429559
      > Skype : Bdebackere
      > brecht@visualantics.net
      >
      >
      >
      >
      >
      >
    • Sep 27 2007 | 11:50 am
      The idea is to create quad_strip ribbon my filling up a matrix, with
      the width of the ribbon being calculated using the crossproduct using
      previous positions :
      vector 1 being :
      current position - previous position
      vector 2 :
      previous position - the position before that
      and then calculating the crossproduct of those 2 vectors, normalizing
      it, and then some stuff with adding the current position to the
      crossproduct and using that value for the even vertices of the
      quad_strip. (I think it sounds clearer in my head, but it is for
      doing something like this : http://www.youtube.com/watch?v=fM1qj_OFY4w )
      On 27 Sep 2007, at 12:56, Ranja Achbar wrote:
      > Hi Brecht,
      >
      > I'm not sure but maybe a shader can help. Parts of the shaders
      > derivatives are don with matrix calculations.
      > It's only an idea. Maybe a bit more complicated. But matrices
      > calculations are much faster on gpu than on cpu.
      >
      > grr.
      > Ranja
      >
      > 2007/9/27, Brecht Debackere :
      > Just a quick question to all the mathbuffs out there...
      >
      > I want to get the crossproduct of 2 vectors, and for this I set up
      > 2 matrices going into jit.expr with the following expression :
      >
      > expr "(in[1].p[2]*in[2].p[3])-(in[1].p[3]*in[2].p[2])" "(in[1].p[3]
      > *in[2].p[1])-(in[1].p[1]-in[2].p[3])" "(in[1].p[1]*in[2].p[2])-(in
      > [1].p[2]*in[1].p[3])"
      >
      > I was wondering if this is correct, and maybe if there's a much
      > more simple expression or object for this...?
      >
      > grtz.
      >
      > Brecht Debackere
      >
      > www.autofasurer.net
      > M+32(0)498319302
      > F+32(0)70429559
      > Skype : Bdebackere
      > brecht@visualantics.net
      >
      >
      >
      >
      >
      >
      Brecht Debackere
      www.autofasurer.net
      M+32(0)498319302
      F+32(0)70429559
      Skype : Bdebackere
      brecht@visualantics.net
    • Sep 27 2007 | 5:50 pm
      Xray.jit.crossproduct maybe can help you.
      www.mat.ucsb.edu/~whsmith/
    • Sep 28 2007 | 10:04 am
      wonderfull. this does exatly what I want, and normalizes as well :)
      thx.
      On 27 Sep 2007, at 19:50, jasmin wrote:
      >
      > Xray.jit.crossproduct maybe can help you.
      > www.mat.ucsb.edu/~whsmith/
      > --
      > jaz
      Brecht Debackere
      www.autofasurer.net
      M+32(0)498319302
      F+32(0)70429559
      Skype : Bdebackere
      brecht@visualantics.net