Re: [Flightgear-devel]

[Russell Suter]

Norman Vine wrote:

Russell Suter writes:
 

Norman Vine wrote:
   

Simply stated the problem is that inorder to rotate an object about an arbritrary
point you *must* do the equivalaent of the following
1) translate object so that it's 'rotation point' is at the 'point of rotation'
2) rotate the object
3) translate the object to it's 'desired' position
 this may not be it's original position depending on
   a) the 'coordinate frame'  the object is described in
       which very likely is the case with an arbritrary VRP
   b) if the coordinate frame is dynamically changing
       as is the case with aerodynamic forces and gravity
       determining the 'frame' in a sophisticated FDM
     

The first item doesn't need to be done per-frame.  It can be done once and
"remembered".
   

Agreed,  and this is AFAICT what is done know although I don't believe the 
dynamic adjustment to the CG is accounted for yet

FWIW AFAICT what isn't done is (3) 

 

I think we're speaking past each other here.  The dynamic adjustment to 
the CG doesn't
happen in the visual, nor should it.  The FDM will corollate the dynamic 
CG to a fixed
VRP.  It's that fixed VRP that is used to translate the 3D model and 
then rotate (steps
3 and 2).

--
Russ
Conway's Law: "The structure of a system tends to mirror the
structure of the group producing it."
     -- Mel Conway Datamation (1968)


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