Hi Tom,
This reads like the perfect (very) early Christmas present! This will keep me
busy on my free "ascension day" tomorrow :-)
Thanks!
Cheers,
Gijs
> Date: Wed, 8 May 2013 11:30:58 +0200
> From: tom...@gmail.com
> To: flightgear-devel@lists.sourceforge.net
> Subject: Re: [Flightgear-devel] New features for 3.0 (?) presentation
>
> Hi Vivian,
>
> 2013/5/7 Vivian Meazza <vivian.mea...@lineone.net>:
> > Thanks, interesting. As a non-Blender user (it makes my brain hurt) the
> > references are a bit obscure.
>
> If you get used to Blender its a really powerful tool (I have problems
> if trying to work with other modelling programs :P) and with using the
> right scripts it gets a very neat tool for creating models for
> FlightGear. For example for a gear scissor just add an armature with
> two bones, add an IK constraint to the second bone and attach an
> element of the scissor to each bone, and you are done. You can watch
> the animation in Blender and using an exporter script now it is
> possible to watch exactly the same animation inside FlightGear. You
> don't need to guess any coordinates/axes/etc. and if you modify and
> object you just have to export it again, without manually modifying
> the animation xml.
>
> > Are the various axes always orthogonal?
>
> There are (currently) only two axes required. The lock-axis and the
> track-axis. They should be orthogonal, as the rotation is only
> possible round the lock-axis. Internally the track-axis is always
> orthonormalized to the lock-axis, as calculations always are performed
> in the plane normal to the lock-axis.
>
> > Can they also be specified in the alternate form:
> >
> > <axis>
> > <x1-m>5.1821</x1-m>
> > <y1-m>0.221496</y1-m>
> > <z1-m>0.794147</z1-m>
> > <x2-m>4.99208</x2-m>
> > <y2-m>0.114133</y2-m>
> > <z2-m>0.842884</z2-m>
> > </axis>
>
> Currently the alternate form is not possible. The problem is that we
> have two axes crossing at the same center, so which of the axes should
> specify the center? Also the center/axis form clearly states where the
> center is located, which is not the case with the alternate form (the
> center is located halfway between the two given points). For the
> rotate animation the exact location of the center along the axis is
> not relevant, but for the tracking animation it is.
> Also as one would probably not create the xml by hand, using multiple
> notations would not gain us anything.
>
> > If non-orthogonal axes are allowed they are difficult in the
> > <center>/<axis> form in the example in the wiki.
> >
> > Perhaps, when you have time, the information could be consolidated in
> >
> > http://wiki.flightgear.org/Howto:Animate_models and
> > fgdata/Docs/model-howto.html
>
> I will do if timer permits :) Yesterday I have added some images. I
> don't know if you have already seen them.
>
> > Looks like valuable work to me: gear scissor links were very difficult with
> > the existing animations.
>
> That was the initial reason for creating it. But now it is also useful
> for creating complex kinematic systems as can be found for landing
> gears and their doors.
>
> Tom
>
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