Jon Berndt wrote:
No. No. No. No. There need not be a prior agreement. The 3D modeler
uses whatever origin suits. It appears in many cases that's the nose.
Yes, yes.
There has to be an understanding of the difference between the frames of
reference (FDM and 3D model). If we are providing the position of the nose,
and the 3D model has some arbitrary origin (that's *not* the nose) then it's
not gonna work.
Then what the H E double toothpicks are these properties for:
*/offsets/x-m* The distance to reposition the model along the x-axis. */offsets/y-m* The distance to reposition the model along the y-axis. */offsets/z-m* The distance to reposition the model along the z-axis. */offsets/heading-deg* The angle by which to rotate the model around the z-axis. */offsets/roll-deg* The angle by which to rotate the model around the x-axis. */offsets/pitch-deg* The angle by which to rotate the model around the y-axis.
I think you understand this. The point is, SOMEONE has to know how to relate the two frames of reference - THAT's what I mean by "agreed-upon".
Of course someone must know this relationship. That doesn't mean they
must be the same point. Someone must not only know the relationship but
also be able to calculate, measure, or WAG a delta x,y,z between these
two frames of reference and put them in the XML wrapper file. But the
understanding need not be a prior agreement!!! So the answer is still NO!
Personally, I have matched FDMs that I did not create with 3D models I did
not create each with different frames of reference using something very similar
to the /offsets/ properties.
Look, I understand 3D graphics. I wrote an application 15 years ago that took reams of simulation data and wrote an animation (frame-by-frame) to videotape using IRIX-GL (before there was OpenGL: http://www.hal-pc.org/~jsb/lambs.jpg). I've created often used shuttle 3D models for rendering under POV-Ray: http://www.hal-pc.org/~jsb/shuttlepov.html.
I mean no disrespect, nor do I question your ability. But, you don't seem to entirely understand
the power of the offsets property. If the FDM reports a position, say the nose, as you intend to
do. Now say that the 3D model has the origin at the tail. All is not lost. As long as someone
can determine the deltas x,y,z between these two fixed points, these deltas become the /offsets/
properties in the XML wrapper file that tell the IG software how to shift the 3D model to the
FDM's reported position. That JSBSim reported the nose is not significant. It's fixed point to
fixed point but they don't need to be the same fixed point.
I am trying to preclude confusion amongst the audience of 3D modelers and
flight model creators.
This is a false sense of security. Not all FDMs will use the nose, nor will all 3D models.
There is another mechanism to correlate the two. That mechanism is the /offsets/ properties
in the wraper file. Reread the section Jim Wilson referenced:
http://www.flightgear.org/Docs/fgfs-model-howto.html#repositioning
And, as Jim confirmed earlier, this mechanism ALWAYS happens, even if the offsets
are 0,0,0.
-- Russ
Conway's Law: "The structure of a system tends to mirror the
structure of the group producing it."
-- Mel Conway Datamation (1968)_______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
