Tom Melly <tom### [at] tomandlucouk> wrote:
: It's a very common beginners misconception. I suspect because beginners
: start with the simple shapes such as sphere etc.

  This is probable the most common reason.
  It's easy to believe that a beginner (and even a not so beginner) could
think something like this:

  Ok, I make a
sphere
{ <1,2,3>, 1
  texture { Wood }
}
  This means that the center of the sphere is at <1,2,3> and its radius is 1.
  Now I'll rotate it around its center so that I get a rotating ball:

sphere
{ <1,2,3>, 1
  texture { Wood }
  rotate <0,45,0>
}

  Oops! What happened? Why it didn't rotate around its center but it moved
to a totally different place?

  The user has confused the center coordinate of the sphere with the
rotation axis center. It's quite natural to think that the center of the
sphere is the center of the rotation axis.
  However, when the user makes something like this, he will be quite
confused:

union
{ sphere { <-.5,0,0>, 1 }
  sphere { <1,0,.5>, 1 }
  texture { Wood }
  rotate <0,45,0>
}

  "Uh... What is the center of this object now? Is it <-.5,0,0>? Is it
<1,0,.5>? Is it somewhere in the middle? What does the rotation actually
do to this object?"

-- 
main(i,_){for(_?--i,main(i+2,"FhhQHFIJD|FQTITFN]zRFHhhTBFHhhTBFysdB"[i]
):_;i&&_>1;printf("%s",_-70?_&1?"[]":" ":(_=0,"\n")),_/=2);} /*- Warp -*/

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