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    pythonsdk doc Matrix manunl error?

    Cinema 4D SDK
    python
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    • chuanzhenC
      chuanzhen
      last edited by

      Hi,
      When I read the matrix manual in python sdk doc, I found that the descriptions of 1 and 2 seem contradictory. In c4d, counter-clockwise rotation (ccw) displays a positive value 90 °, while clockwise rotation (cw) displays a negative value -90 °. However, in image marker 2, the transformation should be clockwise cw 90 ° (i.e. R.B=-90 °), not ccw90 °
      d52ff3e3-4c20-4f0a-a6eb-e20f2284dba3-image.png

      相信我,可以的!

      ferdinandF 1 Reply Last reply Reply Quote 0
      • ferdinandF
        ferdinand @chuanzhen
        last edited by ferdinand

        Hey @chuanzhen,

        Thank you for reaching out to us. I am not quite sure that I can follow. The manual for sure could be improved, as I probably wrote this more technically than it has to be, but I would say the text and image are correct.

        As the manual states, the transform constructed there, is a 90° CCW rotation around the z axis. Which is also what I tried to illustrate below. What is illustrated there, is also more the idea that transforms do not rotate points but rather the coordinate systems in which a point lives.

        I do not see anywhere any negative values printed. That would also contradict a bit the cw and ccw notation as they replace +/-. When we talk about cw/ccw, we have to imagine a plane spanned by the axis perpendicular to the rotation axis, e.g., the XY plane for the z axis in the image below. And imagine there a clock. CCW means then the direction I have marked with the blue arrow below. And when you look at the axis gizmo on the right, you can see it exactly being rotated into that direction.

        602f7d75-8229-4931-8d1f-f8ad8fa37585-image.png

        The other thing which might lead to confusion here, is that humans tend to associate positive numbers with a clockwise motion. But that is exactly the point of that note. The circle functions do the opposite of what humans consider natural. The 2D rotation matrix M(theta) will make a 2D point rotate counter clockwise on the unit circle when you add positiv values to theta and clockwise when you add negative values.

        Cheers,
        Ferdinand

        MAXON SDK Specialist
        developers.maxon.net

        chuanzhenC 1 Reply Last reply Reply Quote 0
        • chuanzhenC
          chuanzhen @ferdinand
          last edited by chuanzhen

          @ferdinand Thank you for explanation. The point of confusion should be marked as 2 in the image. in doc the counterclockwise rotation (ccw) refers to the counterclockwise rotation from the spatial perspective of the image. but for the same rotation, the z-axis should have rotated clockwise(cw). However, in any case, the calculation is correct, only the description is different。
          (Describing a rotation of an axis, it is assumed that a person looks in the negative direction from the positive direction of the axis, and based on this, counterclockwise and clockwise are defined)

          相信我,可以的!

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