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Re: Rotate a 3D vector

by true (Pilgrim)
on Oct 18, 2004 at 00:02 UTC ( #400007=note: print w/replies, xml ) Need Help??


in reply to Rotate a 3D vector

Clarification then. i only need to rotate the vector on the z axis. So the 3dvector point 3 1 3 is rotated 23 degrees on the z axis only. Any help?
jtrue

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Re^2: Rotate a 3D vector
by tachyon (Chancellor) on Oct 18, 2004 at 01:01 UTC

    If you only need to rotate around the Z axis then it is a simple 2D trig problem. The z co-ordinate is invariant as this is our rotational plane.

    sub rotate { my ( $x,$y,$z,$angle ) = @_; $angle = deg2rad($angle); my $x_new = cos($angle)*$x - sin($angle)*$y; my $y_new = sin($angle)*$x + cos($angle)*$y; return $x_new, $y_new, $z; } sub deg2rad { return 3.14159265358979*$_[0]/180 };

    Here is a nice article with a pretty applet Update Corrected error noted by johnnywang

    cheers

    tachyon

      The beauty of concrete! Thanks so much for a perfect example tachyon. Also, a good page about the topic: 2D Math
      jtrue
      just want to point out it's not quite right. You need to first find the polar angle for the original point (x,y), then add the $angle to that for the new polar angle.

      Updated. I'm only refering to the geometric meaning. There is a formula: multiplying by the rotation matrix given by ((cos, -sin),(sin, cos)) (not perl notation!)

Re^2: Rotate a 3D vector
by FoxtrotUniform (Prior) on Oct 18, 2004 at 00:28 UTC

    Well, the quick-and-dirty way to do it is to scale your x component by cos(t) and your y component by sin(t). You might be happier with a matrix-based solution in the long run, though.

    Edit: The math above is, of course, totally bogus. I plead momentary imbecility. johnnywang has the correct solution. D'oh!

    What kind of program are you writing, btw?

    --
    Yours in pedantry,
    F o x t r o t U n i f o r m

    "Lines of code don't matter as long as I'm not writing them." -- merlyn

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