On Freitag, 13. Februar 2004 09:26, Vivian Meazza wrote:
> That's what I did for the Hunter model - seemed to make sense, and I could
> readily derive the CofG from the YASim calculations. I was aided in this
> decision by the fact that the CofG of that aircraft does not move much as
> fuel is consumed. That said, it's marginally easier to draw the model with
> the origin at the nose, and then move it. (not offset - just moving it in
> the drawing package).
Isn't that anoying when you later decide to change something in the visual
model?
You have to move it back again, since your blueprints usually did not match
that origin. Do the modifications, and move it again to match the center of
gravity with the origin ...
> It seems, from a visual point of view, equally valid to leave the origin at
> the nose and to offset the views. Is the a technical reason to prefer one
> or other choice?
No, I don't think so. I like the way JSBSim leaves that choice to the
modeller.
And this discussion for the extra flops doing this transform is really
pointless. The model is transformed anyway before it is painted in the
graphics card. So applying an additional transformation is simply multiplying
the already present 4x4 transform matrix with an additional one. That means
4^3=64 additional flops for this.
In contrast I would guess that an average scene requires painting and
transforming about 10e4 triagles and many more other computations ...
> I remain disconcerted that the visual model appears to roll through 180
> degs vertically on the up and down legs of a loop when in chase or
> helicopter view. Not the end of the world, but lacking realism.
Hmm, I guess that the view direction is computed via some kind of cross
product of the orientation of the aircraft with an earth surface normal
vector. Past that some angular offsets are applied.
So when your aircraft orientation crosses the direction of this surface normal
the cross product has a zero crossing, where some singns of the resulting
vector change afterwards. This is what you observe here. Within a short time
the view direction just looks to the negative of the old direction.
> If you are not confused by now, you don't understand the problem.
What is your confusion?
Greetings
Mathias
--
Mathias Fr�hlich, email: [EMAIL PROTECTED]
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