in reply to Re^5: (OT) moving points from one plane to another
in thread (OT) moving points from one plane to another

Please define "worked fine". Did the 3 specified starting points actually go to the 3 specified target points? If not, then I don't think you've solved your stated problem.

For the first example, if you rotate about the x-axis, then all points on the x-axis have to go back to the x-axis. But in the specification I gave for that example (1, 0, 0) which starts on the x-axis is supposed to wind up at (0, 0, 1) on the z-axis. So you can't possibly do that by rotating around the x-axis.

  • Comment on Re^6: (OT) moving points from one plane to another

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Re^7: (OT) moving points from one plane to another
by merrymonk (Hermit) on Jul 10, 2009 at 16:31 UTC
    Thanks for your continued interest.
    I was a bit overstating the result!
    what I meant was, the points had been rotated to the correct plane.
    I do have to position them correctly in that plane.
    However, as I know how to do this it is not a problem for me.
[reply]
      Yes, that approach will put the points in the correct plane. However the approach that I suggested puts the points in the correct plane, and in the correct position, in one step. Better yet, it works even if the planes are parallel. And its higher dimensional analogs work in any number of dimensions.
[reply]
        the approach that I suggested puts the points in the correct plane, and in the correct position, in one step.

        You make it sound like doing it in one step is a panacea. It isn't.

        For example, if you are modeling planet gears rotating around a sun gear, you cannot combine the counter-rotations in to single matrix. And if the sub gear is not centred at the view origin, then additional discrete steps are required.

        And there many other situations where the the individual parts of a combined transform have to be applied as discrete steps--in the right order--to achieve the final effect. Another example that comes to mind is when you have to translate a set of points to the origin before applying scaling in order to avoid distorting their relative positions.

        As I said before, it is better to understand the discrete steps before attempting to combine them.

        Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
        "Science is about questioning the status quo. Questioning authority".
        In the absence of evidence, opinion is indistinguishable from prejudice.
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