Frieda Reichsman wrote:
Question 1: If you turn on the internal spin around a line, for
example using these commands on your test page:
draw line1 250 (atomno=1) (atomno=2);color draw yellow
spin INTERNAL $line1 30
what is going on with the center of rotation for manipulation with the
mouse? Rotating with the mouse either while the structure is spinning
around its "line-axis" or after turning spin off, it seems that the
structure is now rotating about a point that is unrelated to either the
original center of rotation, or line1, and in fact the center of
rotation is now a point outside the structure.
I think it would be good if the center of rotation for mouse rotation
became a point on line1, perhaps the mid-point of the line. If not,
then IMO it should revert to the original or better yet to the previous
center of rotation (for example if a subset of atoms had been centered).
It's a tricky issue. There is a general XY position on the applet
window around which rotation appears to occur. Then, in addition to
that, there is an x,y,z molecular coordinate point that sits at that
position and does not move. When you spin the molecule, while the XY
position stays fixed, the x,y,z coordinate on top of that position
DOES change.
My implementation assumes that the XY position rotation center,
usually but not always the center of the applet window, should not
change. It allows the x,y,z molecular coordinate point to change, though.
Is that what you are observing?
It's critical that the model not "jump" when spinning starts or
ceases. But we may need some different or at least explicit mechanism
to reset it after spinning, we should add that.
Let's play with it a bit more and see if there is an obvious, natural
solution to this new problem. But whatever that solution is, it should
consist of two parts:
a) defining the XY position in the window around which rotation is to
occur.
b) defining the xyz position in molecular coordinates that should be
the center of rotation.
Question 2: What does
spin off;rotate INTERNAL $line1 10;
do compared to a simple "spin off"? I cannot tell the difference...
Well, it rotates once 10 degrees around $line1. spin off itself would
not do that. I just put the spin off in there to make sure that
spinning was off so it didn't complicate seeing the rotation. I have
to think about what would happen if you are spinning the model and
then while doing that apply a rotation. Probably not a good idea. Test
it and tell me what it does.
Robert M. Hanson, [EMAIL PROTECTED], 507-646-3107
Professor of Chemistry, St. Olaf College
1520 St. Olaf Ave., Northfield, MN 55057
mailto:[EMAIL PROTECTED]
http://www.stolaf.edu/people/hansonr
"Imagination is more important than knowledge." - Albert Einstein
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