Yes, it was quite satisfying to see that the newer "perspectivemodel 11"
(which I developed a while back) actually does match what is done in VRML. I
hadn't ever compared it, and it is a relief to see it works so well. The
issue comes -- perhaps you would like to experiment -- with moving the
center of rotation around the screen, as with CTRL-ALT-left-drag. In many
cases it seems to work properly, but if there is a high zoom level with a
large protein you will see a difference. It's just not quite right yet.
There are three parameters here -- getFieldOfView(), getViewpointPosition(),
and adjustViewpointPosition(). The first one is correct. I think the second
and third ones are not quite right. The perspective model is explained in
http://chemapps.stolaf.edu/jmol/docs/misc/navigation.pdf. As described
there, the sequence is:
1a) translate the fixed rotation center to (0,0,0) (m)
1b) apply the current molecular rotation (m)
1c) apply zoom-based scaling, scalePixelsPerAngstrom (s)
1d) add a Z-translation, modelCenterOffset (s)
I guess this could be all done with translation, rotation, and scaling, and
we may end up doing it that way, but I thought the Viewpoint idea was much
smarter. So I have the Viewpoint position moving the *observer* rather than
applying a translation (1a), Viewpoint orientation instead of a rotation
(1b), and Viewpoint fieldOfView applying (1c).
Now, what about 1d? I think, really, the application of all this is from
last to first (or inner to outer) as presented in the VRML syntax:
Transform{ translation 1a ... children
Transform { rotation 1b ... children
Transform{ scale 1c .. children
Transform { translation 1d ... children
[ ...raw model ]
}
}
}
}
which I now have encoded simply as:
Viewpoint {
position 1a+1d
orientation 1b
fieldOfView 1c
}
Transform { children
[ ...raw model ]
}
I think 1d is not applied quite correctly, but I don't know how to fix it. I
have a feeling that we won't be able to use Viewpoint, but I'm not sure.
We'll see. Feel free to experiment.
Bob
2009/7/21 Angel Herráez <[email protected]>
> That's darned good, Bob. Great job!
>
> The X3D export is now up-to-date with that.
>
>
>
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--
Robert M. Hanson
Professor of Chemistry
St. Olaf College
1520 St. Olaf Ave.
Northfield, MN 55057
http://www.stolaf.edu/people/hansonr
phone: 507-786-3107
If nature does not answer first what we want,
it is better to take what answer we get.
-- Josiah Willard Gibbs, Lecture XXX, Monday, February 5, 1900
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