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Orthogonal projection - embarrassed

  1. Aug 23, 2013 #1
    Hi there

    I am trying to project some 3D points on to the span of two orthogonal vectors.

    v1 = [ -0.1235 -0.9831 0.1352]
    v2 = [ 0.7332 -0.1822 -0.6552]

    I used the orthogonal projection formula

    newpoint = oldpoint-dot(oldpoint,normal(v1,v2))*normal(v1,v2);

    but when I plot it in matlab I dont get the points projected onto the plane.

    Any ideas were I am going wrong?


  2. jcsd
  3. Aug 23, 2013 #2


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    Looks right to me. Have you inspected the intermediate results to see where it diverges from what you expect? (You could start with a simpler pair of vectors.) If still stuck, pls post the intermediate results.
  4. Aug 24, 2013 #3
    Hi there,

    Thank you for the reply. I went mental yesterday because I knew the math was right and subsequent calculations, such as the within plane angle, were all correct.

    The problem I found was with matlabs quiver3 function. It wasn't plotting the vectors correctly and so in the end I made my own and plotted them using + points. Can't put that in a paper lol but at least it demonstrates what I was trying to do.

    Thanks again for thinking about this

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